Introduction
============

Circadian rhythms drive our preferences for wakefulness, periods of activity and sleep. The distribution of the timing of circadian rhythms, or chronotypes, ranges from those individuals that prefer to wake and retire to bed early to those who prefer to go to bed late and rise late, and it is becoming increasingly clear that chronotype impacts on many aspects of life including general health, mental health, cognition and addictive behaviours \[[@B1]\].

Bibliometric analysis measures the number of times an article is cited in the literature and in which particular journal. A citation is received when one article uses another as a reference and the number of citations an article receives can be used as an indicator of impact (an article considered to have greater importance by the research community is more likely to be cited). In addition, citation count also forms the basis for computation of the journal impact factor (IF), which is a widely used measure of journal quality. A review of the most-cited articles within a research field can, therefore, reveal topics of current interest, novel techniques and research trends. The aim of the current study was to identify and analyse the one hundred most-cited publications in the topic of chronotype research.

Methods
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Article identification
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The most-cited chronotype research articles were identified using the Institute for Scientific Information (ISI) Web of science search tool (Thomson Reuters, New York, NY). The ISI web of science is a multidisciplinary database providing a range of bibliometric information indexing over 8500 journals from a wide range of disciplines. Using the topic search term "chronotype" and title search term "\*chronotype\*" combined with the Boolean operator "or" (i.e. returns the value true if either or both of the operands is true) a total of 976 journal articles published between 1990 and 2016 were identified. Searching by the topic term alone returned 842 items, whereas searching by the second term alone returned 321 items. The 100 most cited chronotype papers were identified from this list. The author reviewed the title and abstract for each article to ensure its relevance (one article was excluded in this process and replaced by the next highest article in terms of citation count).

Article analysis
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The following information for each of the top 100 most-cited articles was extracted: 1) authorship, 2) article title, 3) keywords, 4) journal title, 5) year of publication, 6) total number of citations, 7) annual citation count (total number of citations/time since publication), 8) impact factor (IF) , 9) source normalised impact per paper (SNIP), 10) impact per publication (IPP) , 11) the SCImago journal rank (SJR), 12) country of origin (based on the affiliation of the first author at time of publication) and 13) article type (original research, meta-analysis or review).

Results
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The top one hundred journal articles in the field of chronotype research are presented in Table [1](#T1){ref-type="table"}. Total citation count ranged from 29 to 438 (median: 47). The top ranking article was "Life between clocks: Daily temporal patterns of human chronotypes" by T. Roenneberg, A. Wirz-Justice and M. Merrow, published in the *Journal of Biological Rhythms* in 2003. Ranking articles by annual citation count, as compared to total citation count, resulted in a change in position range of --58 to +66 (where a negative number reflects a higher ranking based on annual citation count). The article with the most annual citations (rank change --4) was "Social jetlag and obesity" by T. Roenneberg, published in *Current Biology* in 2012.

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The one hundred most cited chronotype articles ranked in order of total citations received. Where there is equal ranking articles in the same rank received an equal number of citations.

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  Ranking   Article details                                                                                                                                                                                                                                                                                                                                                                       Total Citations
                                                                                                                                                                                                                                                                                                                                                                                                  
  1         Roenneberg, T. Life between clocks: Daily temporal patterns of human chronotypes. JOURNAL OF BIOLOGICAL RHYTHMS 2003; 18(1): 80--90. Keywords: Circadian; clock; human; light; sleep; chronotype                                                                                                                                                                                      438
  2         Wittmann, M. Social jetlag: Misalignment of biological and social time. CHRONOBIOLOGY INTERNATIONAL 2006; 23(1--2): 497--509. Keywords: Chronotype; morningness-eveningness; psychological wellbeing; sleep quality; smoking habits                                                                                                                                                   345
  3         Roenneberg, T. Epidemiology of the human circadian clock. SLEEP MEDICINE REVIEWS 2007; 11(6): 429--438. Keywords: Chronotype; sleep duration; sleep deprivation; entrainment; zeitgeber; light                                                                                                                                                                                        293
  4         Giannotti, F. Circadian preference, sleep and daytime behaviour in adolescence. JOURNAL OF SLEEP RESEARCH 2002; 11(3): 191--199. Keywords: Chronotype; sleep; daytime behaviour; adoclescence; epidemiology                                                                                                                                                                           276
  5         Roenneberg, T. Social Jetlag and Obesity. CURRENT BIOLOGY 2012; 22(10): 939--943. Keywords: Not provided. A video abstract can be viewed here                                                                                                                                                                                                                                         160
  6         Schmidt, C. A time to think: Circadian rhythms in human cognition. COGNITIVE NEUROPSYCHOLOGY 2007; 24(7): 755--789. Keywords: Time of day; circadian; chronotype; cognitive performance; ageing                                                                                                                                                                                       159
  7         Adan, A. Circadian Typology: A Comprehensive Review. CHRONOBIOLOGY INTERNATIONAL 2012; 29(9): 1153--1175. Keywords: Age; circadian typology; chronotype; cognitive performance; morningness-eveningness; personality; psychiatric disorder; sex; shifwork                                                                                                                             152
  8         Bailey, S. Circadian rhythmicity of cortisol and body temperature: Morningness-eveningness effects. CHRONOBIOLOGY INTERNATIONAL 2001; 18(2): 249--261. Keywords: Adult; body temperature; chronotype; circadian rhythm; human; hydrocortisone; larks; owls                                                                                                                            146
  8         Taillard, J. Morningness/eveningness and the need for sleep. JOURNAL OF SLEEP RESEARCH 1999; 8(4): 291--295. Keywords: Chronic sleep deprivation; daytime somnolence; morningness/eveningness; sleelp hygiene; sleep need; sleep/wake habits                                                                                                                                          146
  10        Carrier, J. Sleep and morningness-eveningness in the 'middle' years of life (20--59 y). JOURNAL OF SLEEP RESEARCH 1997; 6(4): 230--237. Keywords: Age; chronotype; circadian rhythms; middle-age; morningness- eveningness; sleep                                                                                                                                                     143
  11        Russo, P. Sleep habits and circadian preference in Italian children and adolescents. JOURNAL OF SLEEP RESEARCH 2007; 16(2): 163--169. Keywords: Chronotype morningness; circadian preference; preadolescence; sleep-habits                                                                                                                                                            114
  11        Paine, S. The epidemiology of morningness/eveningness: Influence of age, gender, ethnicity, and socioeconomic factors in adults (30--49 years). JOURNAL OF BIOLOGICAL RHYTHMS 2006; 21(1): 68--76. Keywords: Morningness/eveningness; chronotype; epidemiology; age; ethnicity; gender; socioeconomic deprivation; work schedules                                                     114
  13        Brown, S. Molecular insights into human daily behavior. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2008; 105(5): 1602--1607. Keywords: Chronotype; circadian; fibroblast; genetics                                                                                                                                                               110
  14        Zavada; A. Comparison of the Munich Chronotype Questionnaire with the Horne-Ostberg's Morningness-Eveningness Score. CHRONOBIOLOGY INTERNATIONAL 2005; 22(2): 267--278. Keywords: Human chronotypes; Sleep; Survey; Horne-Ostberg's Morningness-Eveningness Questionnaire; Munich Chronotype Questionnare                                                                             107
  15        Adan, A. Chronotype and personality-factors in the daily consumption of alcohol and psychostimulants. ADDICTION 1994; 89(4): 455--462. Keywords: N/A                                                                                                                                                                                                                                  100
  16        Hagenauer, M. Adolescent Changes in the Homeostatic and Circadian Regulation of Sleep. DEVELOPMENTAL NEUROSCIENCE 2009; 31(4): 276--284. Keywords: Puberty; chronotype; entrainment; seep deprivation                                                                                                                                                                                 93
  17        Goldstein, D. Time of day, intellectual performance, and behavioral problems in Morning versus Evening type adolescents: Is there a synchrony effect?. PERSONALITY AND INDIVIDUAL DIFFERENCES 2007; 42(3): 431--440. Keywords: Chronotype; Intellectual performance; Adolescence; Time of day; Synchrony effect                                                                       90
  17        Roenneberg, T. The human circadian clock entrains to sun time. CURRENT BIOLOGY 2007; 17(2): R44-R45. Keywords: N/A                                                                                                                                                                                                                                                                    90
  19        Mansour, H. Circadian phase variation in bipolar I disorder. CHRONOBIOLOGY INTERNATIONAL 2005; 22(3): 571--584. Keywords: Circadian; rhythm; chornotype; morningness/eveningness; bipolar disorder; schizophrenia                                                                                                                                                                     86
  20        Taillard, J. The circadian and homeostatic modulation of sleep pressure during wakefulness differs between morning and evening chronotypes. JOURNAL OF SLEEP RESEARCH 2003; 12(4): 275--282. Keywords: alertness; circadian rhythms; electroencephalogram; homeostatic process; morningness/eveningness; spectral analysis                                                            84
  21        Levandovski, R. Depression Scores Associate With Chronotype and Social Jetlag in a Rural Population. CHRONOBIOLOGY INTERNATIONAL 2011; 28(9): 771--778. Keywords: Chronotype; circadian clock; depression; mood disorders; sleep-wake behaviour; social jetlag                                                                                                                        83
  22        Lehnkering, H. Influence of chronotype, season, and sex of subject on sleep behavior of young adults. CHRONOBIOLOGY INTERNATIONAL 2007; 24(5): 875--888. Keywords: Chronotype; sex; season; sleep behaviour; wrist actigraphy                                                                                                                                                         80
  23        Gaspar-Barba, E. Depressive symptomatology is influenced by chronotypes. JOURNAL OF AFFECTIVE DISORDERS 2009; 119(1--3): 100--106. Keywords: Depression; Circadian rhythms; Eveningness--morningness                                                                                                                                                                                  78
  24        Garaulet, M. Timing of food intake predicts weight loss effectiveness. INTERNATIONAL JOURNAL OF OBESITY 2013; 37(4): 604--611. Keywords: Timing of food intake; weight loss; dietary treatment; circadian                                                                                                                                                                             77
  25        Randler, C. Morningness-Eveningness Comparison in Adolescents from Different Countries around the World. CHRONOBIOLOGY INTERNATIONAL 2008; 25(6): 1017--1028. Keywords: Chronotype; circadian rhythm; climate; latitude; longitude                                                                                                                                                    73
  26        Mongrain, V. Circadian and homeostatic sleep regulation in morningness-eveningness. JOURNAL OF SLEEP RESEARCH 2006; 15(2): 162--166. Keywords: N/A                                                                                                                                                                                                                                    72
  27        Hidalgo, M. Relationship between depressive mood and chronotype in healthy subjects. PSYCHIATRY AND CLINICAL NEUROSCIENCES 2009; 63(3): 283--290. Keywords: Chronobiology; chronotype; circadian rhythm; depressive mood; morningness.                                                                                                                                                71
  28        Urban, R. Morningness-eveningness, chronotypes and health-impairing behaviors in adolescents.. CHRONOBIOLOGY INTERNATIONAL 2011; 28(3): 238--47. Keywords: Adolescent; Alcohol; Chronotype; Morningness-eveningness; Physical inactivity; Smoking                                                                                                                                     69
  29        Monk, T. Morningness-eveningness and lifestyle regularity. CHRONOBIOLOGY INTERNATIONAL 2004; 21(3): 435--443. Keywords: N/A                                                                                                                                                                                                                                                           67
  30        Kitamura, S. Evening preference is related to the incidence of depressive states independent of sleep-wake conditions. CHRONOBIOLOGY INTERNATIONAL 2010; 27(9--10): 1797--1812. Keywords: Chronotype; circadian rhythms; depression; eveningess; neuropsychopharmacology; sleep                                                                                                       66
  31        Caci, H. Comparing three morningness scales: Age and gender effects, structure and cut-off criteria. SLEEP MEDICINE 2009; 10(2): 240--245. Keywords: Circadian rhythms; sleep; chronotype; morningness; age; gender; factor analysis; exploratory                                                                                                                                     63
  31        Kudielka, B. Morningness and eveningness: The free cortisol rise after awakening in early birds and night owls. BIOLOGICAL PSYCHOLOGY 2006; 72(2): 141--146. Keywords: Morningness--eveningness; Salivary cortisol; Cortisol awakening rise (CAR); Horne and Östberg Owl-and-Lark-Questionnaire; Hypothalamus--pituitary--adrenal axis (HPA axis) activity; Circadian rhythm          63
  33        Medeiros, A. The relationships between sleep-wake cycle and academic performance in medical students. BIOLOGICAL RHYTHM RESEARCH 2001; 32(2): 263--270. Keywords: Sleep; Sleep duration; Medical students; Academic performance School                                                                                                                                                60
  34        Hansen, J. Nested case-control study of night shift work and breast cancer risk among women in the Danish military. OCCUPATIONAL AND ENVIRONMENTAL MEDICINE 2012; 69(8): 551--556. Keywords: N/A                                                                                                                                                                                      58
  34        Gamble, K. Shift Work in Nurses: Contribution of Phenotypes and Genotypes to Adaptation. PLOS ONE 2011; 6(4). Keywords: N/A                                                                                                                                                                                                                                                           58
  36        Wright, K. Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle. CURRENT BIOLOGY 2013; 23(16): 1554--1558. Keywords: N/A                                                                                                                                                                                                                                          57
  37        Roenneberg, T. Entrainment of the human circadian clock. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2007; 72(): 293--299. Keywords: N/A                                                                                                                                                                                                                                      56
  38        Pedrazzoli, M. Clock polymorphisms and circadian rhythms phenotypes in a sample of the Brazilian population. CHRONOBIOLOGY INTERNATIONAL 2007; 24(1): 1--8. Keywords: Clock;Horne-Ostberg morningness--eveningness score; Circadian chronotype; Genetics of circadian rhythms; Delayed sleep phase syndrome                                                                           55
  39        Selvi, Y. Mood changes after sleep deprivation in morningness-eveningness chronotypes in healthy individuals. JOURNAL OF SLEEP RESEARCH 2007; 16(3): 241--244. Keywords: Circadian; mood; shift work; sleep deprivation                                                                                                                                                               54
  39        Killgore, W. Effects of sleep deprivation and morningness-eveningness traits on risk-taking. PSYCHOLOGICAL REPORTS 2007; 100(2): 613--626. Keywords: N/A                                                                                                                                                                                                                              54
  39        Reilly, T. Diurnal variation in temperature, mental and physical performance, and tasks specifically related to football (soccer). CHRONOBIOLOGY INTERNATIONAL 2007; 24(3): 507--519. Keywords: Body temperature; Circadian rhythms; Sport performance; Soccer                                                                                                                        54
  42        Randler, C. Morningness-eveningness, sleep-wake variables and big five personality factors. PERSONALITY AND INDIVIDUAL DIFFERENCES 2008; 45(2): 191--196. Keywords: Big-five-inventory; Chronotype; Gender differences; Morningness--eveningness; Personality                                                                                                                         53
  43        Randler, C. Morningness-eveningness, habitual sleep-wake variables and cortisol level. BIOLOGICAL PSYCHOLOGY 2010; 85(1): 14--18. Keywords: Adolescents; Awakening cortisol response; Chronotype; Circadian rhythm; Morningness--eveningness                                                                                                                                          52
  43        Atkinson, G. Diurnal variation in cycling performance: Influence of warm-up. JOURNAL OF SPORTS SCIENCES 2005; 23(3): 321--329. Keywords: Clinical trial; publication bias                                                                                                                                                                                                             52
  45        Selvi, Y. Associations between chronotype, sleep quality, suicidality, and depressive symptoms in patients with major depression and healthy controls. CHRONOBIOLOGY INTERNATIONAL 2010; 27(9--10): 1813--1828. Keywords: Chronotype; Depression; Morningness-eveningness; Sleep quality; Suicide                                                                                     51
  46        Hofstra, W. How to assess circadian rhythm in humans: A review of literature. EPILEPSY & BEHAVIOR 2008; 13(3): 438--444. Keywords: Circadian rhythm; Epilepsy; Desynchrony protocol; Constant routine protocol; Dim light melatonin onset; Core body temperature; Cortisol; Sleep parameters; Actigraphy; Chronotype                                                                  50
  46        Randler, C. Differences in sleep and circadian preference between Eastern and Western German adolescents. CHRONOBIOLOGY INTERNATIONAL 2008; 25(4): 565--575. Keywords: Chronotype; Circadian rhythm; Longitude; Morningness-eveningness; Sunlight                                                                                                                                     50
  46        Monk, T. Measuring sleep habits without using a diary: The sleep timing questionnaire. SLEEP 2003; 26(2): 208--212. Keywords: Circadian rhythms; sleep; human; diary; ratings                                                                                                                                                                                                         50
  49        Wirz-Justice, A. Diurnal variation of depressive symptoms.. DIALOGUES IN CLINICAL NEUROSCIENCE 2008; 10(3): 337--43. Keywords: Major depressive disorder; mood; circadian rhythm; sleep regulation; sleep deprivation; synchronization                                                                                                                                                48
  50        Digdon, N. College Students Who Have an Eveningness Preference Report Lower Self-Control and Greater Procrastination. CHRONOBIOLOGY INTERNATIONAL 2008; 25(6): 1029--1046. Keywords: Circadian preference; College students; Self-regulation; Morningness-eveningness; Self-control                                                                                                   47
  50        Refinetti, R. Variability of diurnality in laboratory rodents. JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY 2006; 192(7): 701--714. Keywords: Circadian rhythm; diurnality; locomotor activity; arvicanthis niloticus; meriones unguiculatus; mesocricetus auratus; mus musculus; octodon degus; phodopus sungorus; rattus norvegicus   47
  50        Takeuchi, H. Parental enforcement of bedtime during childhood modulates preference of Japanese junior high school students for eveningness chronotype. CHRONOBIOLOGY INTERNATIONAL 2001; 18(5): 823--829. Keywords: Adolescence; Discipline on bedtime; Gender differences; Japanese children; Junior high school student; Morningness-eveningness                                    47
  53        Besoluk, S. Morningness-Eveningness Preferences and Academic Achievement of University Students. CHRONOBIOLOGY INTERNATIONAL 2011; 28(2): 118--125. Keywords: Achievement; Circadian rhythm; GPA; Morningness-eveningness preference; Teaching time of the day                                                                                                                        46
  53        Randler, C. Associations among Sleep, Chronotype, Parental Monitoring, and Pubertal Development among German Adolescents. JOURNAL OF PSYCHOLOGY 2009; 143(5): 509--520. Keywords: chronotype; circadian rhythm; diurnal preference; morningness-eveningness; puberty                                                                                                                  46
  53        Ong, J. Characteristics of insomniacs with self-reported morning and evening chronotypes.. JOURNAL OF SLEEP MEDICINE 2007; 3(3): 289--94. Keywords: Insomnia; chronotype; morningness; eveningness                                                                                                                                                                                    46
  56        Di Milia, L. Reviewing the Psychometric Properties of Contemporary Circadian Typology Measures. CHRONOBIOLOGY INTERNATIONAL 2013; 30(10): 1261--1271. Keywords: Chronotype; circadian typology; morningness-eveningness preference; psychometric                                                                                                                                      45
  56        Olds, T. Sleep Duration or Bedtime? Exploring the Relationship between Sleep Habits and Weight Status and Activity Patterns. SLEEP 2011; 34(10): 1299--1307. Keywords: Child; screen time; physical activity; bedtime; wake up time                                                                                                                                                   45
  56        Randler, C. Association between morningness-eveningness and mental and physical health in adolescents. PSYCHOLOGY HEALTH & MEDICINE 2011; 16(1): 29--38. Keywords: Adolescents; chronotype; circadian preference; depression; mental health; morningness--eveningness; physical health; quality of life                                                                               45
  56        Fleig, D. Association between chronotype and diet in adolescents based on food logs. EATING BEHAVIORS 2009; 10(2): 115--118. Keywords: Circadian typology; Diet; Diurnal preference; Eating behaviour; Food logs; Nutrition                                                                                                                                                           45
  56        Randler, C. Psychometric properties of the German version of the Composite Scale of Morningness. BIOLOGICAL RHYTHM RESEARCH 2008; 39(2): 151--161. Keywords: Age; circadian rhythms; chronotype; gender; German Composite Scale of Morningness; morningness -- eveningness                                                                                                            45
  61        Merikanto, I. Associations of Chronotype and Sleep With Cardiovascular Diseases and Type 2 Diabetes. CHRONOBIOLOGY INTERNATIONAL 2013; 30(4): 470--477. Chronotype; Circadian; Diurnal; Eveningness; Glucose tolerance; Morningness; Waist circumference                                                                                                                              44
  61        Ahn, Y. Chronotype distribution in bipolar I disorder and schizophrenia in a Korean sample. BIPOLAR DISORDERS 2008; 10(2): 271--275. Keywords: Bipolar disorder; chronotype; schizophrenia                                                                                                                                                                                            44
  63        Tzischinsky, O. Eveningness, Sleep Patterns, Daytime Functioning, and Quality of Life in Israeli Adolescents. CHRONOBIOLOGY INTERNATIONAL 2011; 28(4): 338--343. Keywords: Adolescence, Chronotype; Depressed mood; Morningness-eveningness; Quality of life; Sleep patterns; Sleep-problem behaviours; Sleepiness                                                                    43
  64        Tonetti, L. Morningness-eveningness preference and sensation seeking. EUROPEAN PSYCHIATRY 2010; 25(2): 111--115. Keywords: Sensation seeking; Circadian typology; Gender; University students; Chronotype; Chronobiology                                                                                                                                                              42
  65        Randler, C. Validation of the full and reduced Composite Scale of Morningness. BIOLOGICAL RHYTHM RESEARCH 2009; 40(5): 413--423. Keywords: Chronotype; circadian typology; questionnaire; short form; validation                                                                                                                                                                      41
  65        Waterhouse, J. Identifying some determinants of jet lag, and its symptoms: a study of athletes and other travellers. BRITISH JOURNAL OF SPORTS MEDICINE 2002; 36(1): 54--60. Keywords: N/A                                                                                                                                                                                            40
  67        Merikanto, I. Relation of Chronotype to Sleep Complaints in the General Finnish Population. CHRONOBIOLOGY INTERNATIONAL 2012; 29(3): 311--317. Keywords: Circadian; Eveningness; Hypnotics; Insomnia; Morningness                                                                                                                                                                     40
  67        Allebrandt, K. CLOCK Gene Variants Associate with Sleep Duration in Two Independent Populations. BIOLOGICAL PSYCHIATRY 2010; 67(11): 1040--1047. Keywords: CLOCK; sleep duration; clock genes; MCTQ; short sleepers; long sleepers                                                                                                                                                    40
  67        Jankowski, K. Diurnal variation in energetic arousal, tense arousal, and hedonic tone in extreme morning and evening types. CHRONOBIOLOGY INTERNATIONAL 2008; 25(4): 577--595. Keywords: Chronotype; MEQ; Diurnal rhythm; Mood                                                                                                                                                        40
  70        Preckel, F. Chronotype, cognitive abilities, and academic achievement: A meta-analytic investigation. LEARNING AND INDIVIDUAL DIFFERENCES 2011; 21(5): 483--492. Keywords: Chronotype; Morningness--eveningness; Meta-analysis; Cognitive ability; Academic achievement; Grades; Prediction                                                                                           39
  71        Borisenkov, M. Chronotype, sleep length, and school achievement of 11-to 23-year-old students in northern european russia. CHRONOBIOLOGY INTERNATIONAL 2010; 27(6): 1259--1270. Keywords: Chronotype; Circadian rhythm; College students; Northern latitudes; School achievements; School children; Sleep length                                                                      38
  71        Werner, H. Assessment of Chronotype in Four- to Eleven-Year-Old Children: Reliability and Validity of the Children's ChronoType Questionnaire (CCTQ). CHRONOBIOLOGY INTERNATIONAL 2009; 26(5): 992--1014. Keywords: Chronotype; Midsleep point; Morningness/eveningness; Validity; Children                                                                                           38
  71        Cuninkova, L. Peripheral circadian oscillators - Interesting mechanisms and powerful tools. MOLECULAR AND BIOPHYSICAL MECHANISMS OF AROUSAL, ALERTNESS, AND ATTENTION 2008; 1129(): 358--370. Keywords: Circadian; clock; peripheral; chronotype; genetics                                                                                                                            38
  74        Vollmer, C. Outdoor Light at Night (LAN) Is Correlated With Eveningness in Adolescents. CHRONOBIOLOGY INTERNATIONAL 2012; 29(4): 502--508. Keywords: Adolescents; Chronotype; CSM; Electronic screen media; Intake of stimulants; Light at night (LAN); Light pollution; Midpoint of sleep; Remote sensing                                                                            37
  74        Mongrain, V. Chronotype and sex effects on sleep architecture and quantitative sleep EEG in healthy young adults. SLEEP 2005; 28(7): 819--827. Keywords: Morningness-eveningness; sleep; spectral analysis; circadian rhythms; human; sex difference; sleep regulation                                                                                                                37
  74        Challet, E. Circadian organization in a diurnal rodent, Arvicanthis ansorgei Thomas 1910: Chronotypes, responses to constant lighting conditions, and photoperiodic changes. JOURNAL OF BIOLOGICAL RHYTHMS 2002; 17(1): 52--64. Keywords: Locomotor activity; rhythm; period; phase; day length; entrainment; Arvicanthis                                                             37
  74        Labyak, S. Rhythm chronotypes in a diurnal rodent, Octodon degus. AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY 1997; 273(3): R1058-R1066. Keywords: N/A                                                                                                                                                                                           37
  78        Jonason, P. Creatures of the night: Chronotypes and the Dark Triad traits. PERSONALITY AND INDIVIDUAL DIFFERENCES 2013; 55(5): 538--541. Keywords: Dark Triad; Narcissism; Psychopathy; Machiavellianism; Morningness: eveningness; Chronotype; Evolutionary psychology                                                                                                               34
  78        Reutrakul, S. Chronotype Is Independently Associated With Glycemic Control in Type 2 Diabetes. DIABETES CARE 2013; 36(9): 2523--2529. Keywords: N/A                                                                                                                                                                                                                                   34
  78        Allebrandt, K. A K-ATP channel gene effect on sleep duration: from genome-wide association studies to function in Drosophila. MOLECULAR PSYCHIATRY 2013; 18(1): 122--132.Keywords: N/A                                                                                                                                                                                                34
  78        Hsu, C. Associations Between Chronotypes, Psychopathology, and Personality Among Incoming College Students. CHRONOBIOLOGY INTERNATIONAL 2012; 29(4): 491--501. Keywords: Chronotypes; Evening type; Morningness-eveningness; Personality; Psychopathology; Young adults                                                                                                               34
  78        Di Milia, L. Demographic factors; fatigue, and driving accidents: An examination of the published literature. ACCIDENT ANALYSIS AND PREVENTION 2011; 43(2): 516--532. Keywords: Fatigue; Demographics; Driving accidents; Working arrangement; Circadian chronotype; Personality traits                                                                                               34
  78        Wittmann, M. Decreased Psychological Well-Being in Late 'Chronotypes' Is Mediated by Smoking and Alcohol Consumption. SUBSTANCE USE & MISUSE 2010; 45(1--2): 15--30. Keywords: Cigarette; smoking; alcohol; chronotype; sleep-wake cycle; mood                                                                                                                                        34
  78        Caci, H. Inattentive Symptoms of ADHD Are Related to Evening Orientation. JOURNAL OF ATTENTION DISORDERS 2009; 13(1): 36--41. Keywords: Attention; impulsivity; hyperactivity; attention-deficit/hyperactivity disorder; circadian rhythms; chronotype; morningness; factor analysis; exploratory                                                                                     34
  85        Osland, T. Association Study of a Variable-Number Tandem Repeat Polymorphism in the Clock Gene PERIOD3 and Chronotype in Norwegian University Students. CHRONOBIOLOGY INTERNATIONAL 2011; 28(9): 764--770. Keywords: Association study; Chronotype; Circadian rhythm; Diurnal preference; Genotype; Morningness/eveningness; PER3                                                     33
  85        Leonhard, C. In Sync with the Family: Children and Partners Influence the Sleep-Wake Circadian Rhythm and Social Habits of Women. CHRONOBIOLOGY INTERNATIONAL 2009; 26(3): 510--525. Keywords: Children; Circadian rhythm; Family synchronization; Parents; Partner                                                                                                                   33
  85        Rea, M. A new approach to understanding the impact of circadian disruption on human health. JOURNAL OF CIRCADIAN RHYTHMS 2008; (6) Keywords: N/A                                                                                                                                                                                                                                      33
  88        Selvi, Y. Chronotype Differences in Suicidal Behaviour and Impulsivity Among Suicide Attempters. CHRONOBIOLOGY INTERNATIONAL 2011; 28(2): 170--175. Keywords: Biological rhythms; Chronotype; Circadian; Impulsivity; Morningness/eveningness; Suicide                                                                                                                                32
  88        Kantermann, T. Shift-work research: Where do we stand, where should we go?. SLEEP AND BIOLOGICAL RHYTHMS 2010; 8(2): 95--105. Keywords: N/A                                                                                                                                                                                                                                           32
  88        Vernet, C. Idiopathic Hypersomnia with and without Long Sleep Time: A Controlled Series of75 Patients. SLEEP 2009; 32(6): 753--759. Keywords: Hypersomnia; long sleep time; MSLT                                                                                                                                                                                                      32
  88        Mongrain, V. Increased homeostatic response to behavioral sleep fragmentation in morning types compared to evening types. SLEEP 2007; 30(6): 773--780. Keywords: Morningness-eveningness; sleep fragmentation; sleep; EEG spectral analysis; circadian rhythms; human; sleep regulation                                                                                               32
  88        Goulet, G. Daily light exposure in morning-type and evening-type individuals. JOURNAL OF BIOLOGICAL RHYTHMS 2007; 22(2): 151--158. Keywords: Morningness-eveningness; chronotype; light exposure; circadian phase; circadian period; sleep schedule; ambulatory recordings; entrainment                                                                                               32
  93        Pagani, L. The Physiological Period Length of the Human Circadian Clock In Vivo Is Directly Proportional to Period in Human Fibroblasts. PLOS ONE 2010; 5(10). Keywords: N/A                                                                                                                                                                                                          31
  93        Monk, T. A sleep diary and questionnaire study of naturally short sleepers. JOURNAL OF SLEEP RESEARCH 2001; 10(3): 173--179. Keywords: N/A                                                                                                                                                                                                                                            31
  95        Lucassen, E. Evening Chronotype Is Associated with Changes in Eating Behavior, More Sleep Apnea, and Increased Stress Hormones in Short Sleeping Obese Individuals. PLOS ONE 2013; 8(3). Keywords: N/A                                                                                                                                                                                30
  95        Pagani, L. Serum factors in older individuals change cellular clock properties. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2011; 108(17): 7218--7223. Keywords: Chronobiology; peripheral oscillators; human behaviour                                                                                                                           30
  95        Randler, C. Age and Gender Differences in Morningness-Eveningness During Adolescence. JOURNAL OF GENETIC PSYCHOLOGY 2011; 172(3): 302--308. Keywords: Morningness--eveningness; chronotype; adolescents; age; gender; Turkey                                                                                                                                                          30
  95        Matchock, R. Chronotype and time-of-day influences on the alerting, orienting, and executive components of attention. EXPERIMENTAL BRAIN RESEARCH 2009; 192(2): 189--198. Keywords: Alertness; attention; chronotype; conflict; diurnal; eveningness; morningness; time-of-day                                                                                                        30
  95        Schubert, E. Association between chronotype and the constructs of the Three-Factor-Eating-Questionnaire. APPETITE 2008; 51(3): 501--505. Keywords: Circadian typology; Composite Scale of Morningness; Diet, Dietary restraint; Disinhibition; Diurnal preference; Eating behaviour; Morningness--eveningness; Perceived hunger; Three-Factor-Eating-Questionnaire                    30
  100       Juda, M. Chronotype Modulates Sleep Duration, Sleep Quality, and Social Jet Lag in Shift-Workers. JOURNAL OF BIOLOGICAL RHYTHMS 2013; 28(2): 141--151. Keywords: Chronotype; MCTQ shift; shift-work; circadian misalignment; social jet lag; sleep duration; sleep quality age                                                                                                        29
  --------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -----------------

N/A = not applicable (keywords either not available or not included in the journal format).

The journal with the most publications in the top one-hundred was *Chronobiology International* (*n* = 30), followed by the *Journal of Sleep Research* (*n* = 8) and *Sleep* and *Journal of Biological Rhythms* (both, *n* = 5). The median/range IF, SNIP, IPP and SJR was, respectively, 3.11/0.53--13.31, 1.24/0.43--3.10, 3.27/0.64--10.58, 1.37/0.25--5.93 (see Table [2](#T2){ref-type="table"}).

###### 

Journal in which the one hundred most cited chronotype articles were published ranked by number of articles. Where there is equal ranking articles in the same rank published an equal number of articles.

  -------------------------------------------------------------------------------------------- ------------- -------- ------- -------- -------
  Journal                                                                                      No Articles   IF       SNIP    IPP      SJR
                                                                                                                                       
  CHRONOBIOLOGY INTERNATIONAL                                                                  30            3.540    1.137   3.339    1.264
  JOURNAL OF SLEEP RESEARCH                                                                    8             3.093    1.505   3.337    1.283
  SLEEP                                                                                        5             4.793    1.907   4.927    2.053
  JOURNAL OF BIOLOGICAL RHYTHMS                                                                5             2.824    0.961   2.824    1.553
  CURRENT BIOLOGY                                                                              3             9.571    1.490   5.419    3.732
  PLOS ONE                                                                                     3             3.057    1.034   3.270    1.300
  PERSONALITY AND INDIVIDUAL DIFFERENCES                                                       3             1.861    1.183   2.156    1.134
  BIOLOGICAL RHYTHM RESEARCH                                                                   3             0.695    0.468   0.802    0.245
  PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA              2             9.423    2.542   9.238    5.781
  BIOLOGICAL PSYCHOLOGY                                                                        2             3.234    1.153   3.278    1.516
  MOLECULAR PSYCHIATRY                                                                         1             13.314   2.488   10.575   5.930
  BIOLOGICAL PSYCHIATRY                                                                        1             11.212   2.165   8.905    4.775
  DIABETES CARE                                                                                1             8.420    3.091   7.849    4.190
  SLEEP MEDICINE REVIEWS                                                                       1             7.341    3.095   7.958    2.708
  BRITISH JOURNAL OF SPORTS MEDICINE                                                           1             5.025    2.008   4.072    1.596
  ADDICTION                                                                                    1             4.927    1.841   4.080    2.036
  BIPOLAR DISORDERS                                                                            1             4.882    1.633   5.186    2.774
  EUROPEAN PSYCHIATRY                                                                          1             3.912    1.000   2.500    1.341
  OCCUPATIONAL AND ENVIRONMENTAL MEDICINE                                                      1             3.745    1.650   3.129    1.401
  JOURNAL OF AFFECTIVE DISORDERS                                                               1             3.570    1.390   3.668    1.691
  JOURNAL OF ATTENTION DISORDERS                                                               1             3.384    1.020   2.351    1.046
  SLEEP MEDICINE                                                                               1             3.339    1.224   3.305    1.174
  AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY             1             3.168    \*      \*       \*
  APPETITE                                                                                     1             3.125    1.260   3.034    1.218
  DEVELOPMENTAL NEUROSCIENCE                                                                   1             2.898    0.857   3.176    1.490
  EPILEPSY & BEHAVIOR                                                                          1             2.332    \*      \*       \*
  JOURNAL OF SPORTS SCIENCES                                                                   1             2.142    0.579   2.525    1.178
  EXPERIMENTAL BRAIN RESEARCH                                                                  1             2.057    1.894   2.432    1.193
  JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY   1             1.988    \*      \*       \*
  EATING BEHAVIORS                                                                             1             1.962    0.741   1.744    0.592
  LEARNING AND INDIVIDUAL DIFFERENCES                                                          1             1.630    1.326   1.956    1.083
  COGNITIVE NEUROPSYCHOLOGY                                                                    1             1.444    0.610   1.867    1.081
  PSYCHOLOGY HEALTH & MEDICINE                                                                 1             1.347    \*      \*       \*
  JOURNAL OF PSYCHOLOGY                                                                        1             1.250    \*      \*       \*
  SUBSTANCE USE & MISUSE                                                                       1             1.133    \*      \*       \*
  SLEEP AND BIOLOGICAL RHYTHMS                                                                 1             0.628    0.426   0.774    0.308
  JOURNAL OF GENETIC PSYCHOLOGY                                                                1             0.542    0.477   0.843    0.323
  PSYCHOLOGICAL REPORTS                                                                        1             0.530    0.434   0.635    0.287
  COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY                                          1             \*       0.915   4.183    2.934
  DIALOGUES IN CLINICAL NEUROSCIENCE                                                           1             \*       1.400   4.650    1.974
  JOURNAL OF CIRCADIAN RHYTHMS                                                                 1             \*       0.640   1.467    0.567
  JOURNAL OF SLEEP MEDICINE                                                                    1             \*       \*      \*       \*
  MOLECULAR AND BIOPHYSICAL MECHANISMS OF AROUSAL, ALERTNESS, AND ATTENTION                    1             \*       \*      \*       \*
  -------------------------------------------------------------------------------------------- ------------- -------- ------- -------- -------

For abbreviations please see main text.

Figure [1](#F1){ref-type="fig"} shows the distribution of publications by year. The year with the most publications from the top one-hundred most-cited articles was 2007 (*n* = 14) (Figure [1](#F1){ref-type="fig"}). The most frequent first author was Randler, C (*n* = 9) (Table [3](#T3){ref-type="table"}), and the majority of articles originated in Germany (*n* = 26) (Figure [2](#F2){ref-type="fig"}).

![Distribution of top 100 publications by year (grey bars) and total publications per year (dark grey squares).](jcr-15-146-g1){#F1}

###### 

First authors who contributed two or more of the top one hundred chronotype articles.

  --------------- -------------
  First Author    No Articles
                  
  Randler, C      9
  Roenneberg, T   5
  Mongrain, V     3
  Monk, T         3
  Selvi, Y        3
  Adan, A         2
  Allebrandt, K   2
  Caci, H         2
  Di Milia, L     2
  Merikanto, I    2
  Pagani, L       2
  Taillard, J     2
  Wittmann, M     2
  --------------- -------------

![Number of publications as a function of country of origin.](jcr-15-146-g2){#F2}

The most frequent article type was original research (*n* = 89) and of these 54 (61%) were entirely questionnaire based. Ten review articles and one meta-analysis were also included in the top 100 most-cited articles.

Discussion
==========

Bibliometrics are frequently used in the library and information sciences to provide quantitative analysis of academic literature. This approach can be used to explore the impact of a field or research discipline, the impact of an individual/group of researchers or the impact of a particular paper.

The top one-hundred most cited articles in the field of chronotype were cited between 438 and 29 times. Annual citation count was also considered to evaluate current impact of an article. Although there were a number of substantial shifts in ranking, the articles with the top 5 *annual* citation counts were also in the top seven for *total* citation count thereby suggesting both historical importance and current relevance.

Perhaps not surprisingly, nearly 50% of the most-cited papers were published in discipline-related journals (*Chronobiology International, Journal of Sleep Research, Sleep and Journal of Biological Rhythms, Biological Rhythm Research*). The remaining publications encompassed a broad range of disciplines (e.g. psychology, psychiatry, nutrition and addiction) suggesting a wide audience and broad appeal of chronotype research.

With regard to year of publication, an interesting pattern of results was revealed. Seventy-six percent of the most cited articles were published post 2006 (Figure [1](#F1){ref-type="fig"}). The large increase in most-cited publications from 2007 onwards was mirrored (with a lag) by an equally sharp increase in total publications per year. The broad range of journal disciplines represented in the top one hundred most cited articles and the surge in publication rate suggest expanding interest in chronotype generally and increasing awareness of the impact of chronotype on a broad range of factors including cognitive function, general health and psychopathology.

Over a quarter of the top one hundred most cited articles originated from Germany. It seems unlikely that this can be attributed to the size of the scientific community or underpinning resources as this number outstripped the U.S. Rather, this figure appears to reflect the work of two principal investigators, Professor Till Roenneberg (Institute of Medical Psychology, Ludwig-Maximilian University, Munich) and Christoph Randler (University of Tübingen).

Lastly, the majority of most-cited articles represented original research, of which 61% were entirely questionnaire based. There appears to be scope to draw from other research disciplines and include a broader range of techniques and methodologies (e.g. neuroimaging, endocrinology and genetics).

Blibliometric analyses can provide insight into the development of a research field and highlight patterns, strengths and research trends over time. The approach is not without its limitations, however, and these should be taken into consideration when interpreting the current data. For example, total citation count may preferentially bias older articles. To account for this, a time adjusted metric (annual citations) was also reported. Second, the articles identified for inclusion are dependent on the search parameters selected. In the current study only publications from 1990 onwards were included and the search term was restricted to chronotype. The choice of search parameters may, therefore, exclude influential papers (e.g. Horne, J. A., & Östberg, O. (1976). A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. *International Journal of Chronobiology, 4*(2), 97--110). Further considerations are obliteration by incorporation (influential research subsumed into common knowledge and therefore not cited), omission-bias (ignoring contradictory results) and self-citation. Finally, a direct comparison of the top citation counts across fields or disciplines is challenging and may detract from the importance of individual contributions to a small, specialised field of research. For example, the most cited genetics article had 22,085 citations. A search using the term sleep revealed a top-cited article with 6,365 citations. Nevertheless, the data presented in this report suggest that interest in chronotype research is increasing. Future chronotype citation reports may benefit from the inclusion of altmetrics that allows a broader analysis of the use of scholarly articles and includes not only citations but views, downloads etc.

In conclusion, the importance of assessing impact (on both the research field and the broader general public) is becoming increasingly important, and many research-funding bodies use impact as a means to justify their spending to governments and donors. The bibliometic analysis reported here included the top one hundred most cited papers in the topic of chronotype research. The data provide insight into the impact of chronotype research, the relative importance of a journal within the field (IF), the impact of a particular article (as indexed by citation count) and the contributions by specific researchers or groups.

Disclosure statement
====================

The author does not have any financial interest or benefit arising from the direct application of this research.

Ethics statement
================

This study was a bibliometric analysis that did not include procedures involving animal or human participants and was, therefore, exempt from the requirement for ethical review and approval.

Competing Interests
===================

The author has no competing interests to declare.
