***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background Tinnitus is a common condition in adults ; however , the pathophysiology of tinnitus remains unclear , and no large population -based study has assessed the associated risk factors . The aim of this study was to analyze the prevalence and associated risk factors of tinnitus . Methods We conducted a cross-sectional study using data from the Korea National Health and Nutrition Examination Survey , with 19,290 participants ranging in age from 20 to 98 years old , between 2009 and 2012 . We investigated the prevalence of tinnitus using a question naire and analyzed various possible factors associated with tinnitus using simple and multiple logistic regression analysis with complex sampling . Results The prevalence of tinnitus was 20.7 % , and the rates of tinnitus associated with no discomfort , moderate annoyance , and severe annoyance were 69.2 % , 27.9 % , and 3.0 % , respectively . The prevalence of tinnitus and the rates of annoying tinnitus increased with age . The adjusted odds ratio ( AOR ) of tinnitus was higher for females , those with a smoking history , those reporting less sleep ( ≤ 6 h ) , those with more stress , those in smaller households , those with a history of hyperlipidemia osteoarthritis , rheumatoid arthritis , asthma , depression , thyroid disease , an abnormal tympanic membrane , unilateral hearing loss , bilateral hearing loss , noise exposure from earphones , noise exposure at the workplace , noise exposure outside the workplace , and brief noise exposure . Additionally , unemployed individuals and soldiers had higher AORs for tinnitus . The AOR of annoying tinnitus increased with age , stress , history of hyperlipidemia , unilateral hearing loss , and bilateral hearing loss . Conclusions Tinnitus is very common in the general population and is associated with gender , smoking , stress , sleep , hearing loss , hyperlipidemia , osteoarthritis , rheumatoid arthritis , asthma , depression , and thyroid disease history BACKGROUND Tinnitus is common ; however , few risk factors for tinnitus are known . METHODS We examined cross-sectional relations between several potential risk factors and self-reported tinnitus in 14,178 participants in the 1999 - 2004 National Health and Nutrition Examination Surveys , a nationally representative data base . We calculated the prevalence of any and frequent ( at least daily ) tinnitus in the overall US population and among subgroups . Logistic regression was used to calculate odds ratios ( OR ) and 95 % confidence intervals ( CI ) after adjusting for multiple potential confounders . RESULTS Approximately 50 million US adults reported having any tinnitus , and 16 million US adults reported having frequent tinnitus in the past year . The prevalence of frequent tinnitus increased with increasing age , peaking at 14.3 % between 60 and 69 years of age . Non-Hispanic whites had higher odds of frequent tinnitus compared with other racial/ethnic groups . Hypertension and former smoking were associated with an increase in odds of frequent tinnitus . Loud leisure-time , firearm , and occupational noise exposure also were associated with increased odds of frequent tinnitus . Among participants who had an audiogram , frequent tinnitus was associated with low-mid frequency ( OR 2.37 ; 95 % CI , 1.76 - 3.21 ) and high frequency ( OR 3.00 ; 95 % CI , 1.78 - 5.04 ) hearing impairment . Among participants who were tested for mental health conditions , frequent tinnitus was associated with generalized anxiety disorder ( OR 6.07 ; 95 % CI , 2.33 - 15.78 ) but not major depressive disorder ( OR 1.58 ; 95 % CI , 0.54 - 4.62 ) . CONCLUSIONS The prevalence of frequent tinnitus is highest among older adults , non-Hispanic whites , former smokers , and adults with hypertension , hearing impairment , loud noise exposure , or generalized anxiety disorder . Prospect i ve studies of risk factors for tinnitus are needed Aims : To explore the interaction of smoking and occupational exposure to noise as risk factors for  hearing difficulty in the general population . Methods : A question naire was mailed to 21 201 adults of working age , selected at r and om from the age-sex registers of 34 British general practice s , and to 993 members of the armed services , r and omly selected from pay records . Questions were asked about smoking habits , years spent in a noisy occupation , difficulty in hearing conversation , and wearing of a hearing aid .  Associations of hearing difficulty with smoking habit were examined by logistic regression and compared across strata of noise exposure , with adjustment for potential confounders . Results : Around half of the respondents had ever smoked , and half of these still smoked . Among 10 418 who provided details on hearing , 348 were classed as having moderate and 311 as having severe hearing difficulty . Risk of hearing difficulty was 3–5-fold higher in those employed for > 5 years in noisy work compared with those never employed in a noisy job . Within strata of noise exposure ( including those who had never worked in a noisy job ) , ex- and current smokers had a higher risk of hearing difficulty than lifetime non-smokers . The additional risks were small compared with those of long term noise exposure , and the combination of effects was more consistent with an additive than a multiplicative interaction . Conclusions : Smoking may adversely affect hearing , and workers should be encouraged to refrain from both smoking and exposure to noise . However , the extra risk to hearing incurred by smoking in high ambient noise levels is small relative to that from the noise itself , which should be the main target for preventive measures This paper is the second in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine , an acetylcholinomimetic drug , on aggregate responses within the auditory pathway . In a single-blind procedure , auditory responses were obtained from 20 normal-hearing , non-smokers ( 10 male ) under two conditions ( nicotine , placebo ) . The effects of nicotine on central , mesogenous responses of the auditory system ( middle latency and 40-Hz responses ) are described in this second paper . Results indicated that transdermal administration of nicotine to non-smokers does significantly affect the central , neural transmission of acoustic information . Na-Pa amplitude and Nb latency of the middle latency response and latency measures of the 40-Hz response were acutely altered by the presence of nicotine OBJECTIVE : To test the feasibility of creating a valid and reliable checklist with the following features : appropriate for assessing both r and omised and non-r and omised studies ; provision of both an overall score for study quality and a profile of scores not only for the quality of reporting , internal validity ( bias and confounding ) and power , but also for external validity . DESIGN : A pilot version was first developed , based on epidemiological principles , review s , and existing checklists for r and omised studies . Face and content validity were assessed by three experienced review ers and reliability was determined using two raters assessing 10 r and omised and 10 non-r and omised studies . Using different raters , the checklist was revised and tested for internal consistency ( Kuder-Richardson 20 ) , test-retest and inter-rater reliability ( Spearman correlation coefficient and sign rank test ; kappa statistics ) , criterion validity , and respondent burden . MAIN RESULTS : The performance of the checklist improved considerably after revision of a pilot version . The Quality Index had high internal consistency ( KR-20 : 0.89 ) as did the subscales apart from external validity ( KR-20 : 0.54 ) . Test-retest ( r 0.88 ) and inter-rater ( r 0.75 ) reliability of the Quality Index were good . Reliability of the subscales varied from good ( bias ) to poor ( external validity ) . The Quality Index correlated highly with an existing , established instrument for assessing r and omised studies ( r 0.90 ) . There was little difference between its performance with non-r and omised and with r and omised studies . Raters took about 20 minutes to assess each paper ( range 10 to 45 minutes ) . CONCLUSIONS : This study has shown that it is feasible to develop a checklist that can be used to assess the method ological quality not only of r and omised controlled trials but also non-r and omised studies . It has also shown that it is possible to produce a checklist that provides a profile of the paper , alerting review ers to its particular method ological strengths and weaknesses . Further work is required to improve the checklist and the training of raters in the assessment of external validity Aims : To determine the prevalence of  self reported hearing difficulties and tinnitus in working aged people from the general population , and to estimate the risks from occupational exposure to noise and the number of attributable cases nationally . Methods : A question naire was mailed to 22 194 adults of working age selected at r and om from the age – sex registers of 34 British general practice s ( 21 201 subjects ) and from the central pay records of the British armed services ( 993 subjects ) . Information was collected on years of employment in a noisy job ; and whether the respondent wore a hearing aid , had difficulty in hearing conversation , or had experienced persistent tinnitus over the past year . Associations of hearing difficulty and tinnitus with noise exposure were examined by logistic regression , with adjustment for age , sex , smoking habits , and frequent complaints of headaches , tiredness , or stress . The findings were expressed as prevalence ratios ( PRs ) with associated 95 % confidence intervals ( CIs ) . Attributable numbers were calculated from the relevant PRs and an estimate of the prevalence of occupational exposure to noise nationally . Results : Some 2 % of subjects reported severe hearing difficulties ( wearing a hearing aid or having great difficulty in both ears in hearing conversation in a quiet room ) . In men , the prevalence of this outcome rose steeply with age , from below 1 % in those aged 16–24 years to 8 % in those aged 55–64 . The pattern was similar in women , but severe hearing loss was only about half as prevalent in the oldest age b and . Tinnitus was far more common in subjects with hearing difficulties . In both sexes , after adjustment for age , the risk of severe hearing difficulty and persistent tinnitus rose with years spent in a noisy job . In men older than 35 years with 10 or more years of exposure , the PR for severe hearing difficulty was 3.8 ( 95 % CI 2.4 to 6.2 ) and that for persistent tinnitus 2.6 ( 95 % CI 2.0 to 3.4 ) in comparison with those who had never had a noisy job . Nationally , some 153 000 men and 26 000 women aged 35–64 years were estimated to have severe hearing difficulties attributable to noise at work . For persistent tinnitus the corresponding numbers were 266 000 and 84 000 . Conclusions : Significant hearing difficulties and tinnitus are quite common in men from the older working age range . Both are strongly associated with years spent in a noisy occupation — a predominantly male exposure . The national burden of hearing difficulties attributable to noise at work is substantial This paper is the first in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine , an acetylcholinomimetic drug , on aggregate responses within the auditory pathway . In a single-blind procedure , auditory responses were obtained from 20 normal-hearing , non-smokers ( 10 male ) under two conditions ( nicotine , placebo ) . After the drug session , plasma tests revealed a subject 's nicotine concentration . The effects of nicotine on early , exogenous responses of the auditory system ( otoacoustic emissions and auditory brainstem potentials ) are described in this first paper . Results indicated that transdermal administration of nicotine to non-smokers does not significantly affect cochlear activity but does acutely affect the neural transmission of acoustic information . Overall , otoacoustic emissions were unaffected by transdermal nicotine while wave I of the auditory brainstem response was significantly increased in latency and decreased in amplitude 
    Output:
    
CONCLUSION There is sufficient evidence that smoking is associated with tinnitus .
As the review mainly consists of cross-sectional studies , the observed correlation does not give evidence of a causal relationship .