***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 Low levels of physical activity are characteristic in preschoolers . To effectively promote physical activity , it is necessary to underst and factors that influence young children 's physical activity . The present study aim ed to investigate how physical activity levels are influenced by environmental factors during recess in preschool . Methods Preschool playground observations and pedometry during recess were carried out in 39 r and omly selected preschools ( 415 boys and 368 girls ; 5.3 ± 0.4 years old ) . In order to examine the contribution of playground variables to physical activity levels , taking adjustment for clustering of subjects within preschools into account , multilevel analyses were conducted . Results During recess boys took significantly more steps per minute than girls ( 65 ± 36 versus 54 ± 28 steps/min ) . In both genders higher step counts per minute were significantly associated with less children per m2 and with shorter recess times . Only in boys a hard playground surface was a borderline significant predictor for higher physical activity levels . In girls higher step counts were associated with the presence of less supervising teachers . Playground markings , access to toys , the number of playing or aim ing equipment pieces and the presence of vegetation or height differences were not significant physical activity predictors in both genders . Conclusion In preschool children physical activity during outdoor play is associated with modifiable playground factors . Further study is recommended to evaluate if the provision of more play space , the promotion of continued activity by supervisors and the modification of playground characteristics can increase physical activity levels in preschoolers Objective : To investigate whether the distance covered in the  six minute walk test  was affected by walking with a group of others in comparison with performing the test alone . Methods : Eight healthy men ( mean ( SD ) age 21.0 ( 0.9 ) years ) and eight healthy women ( mean ( SD ) age 20.8 ( 2.0 ) years ) performed in r and om order two six minute walk tests either alone or in a group of four on two separate occasions one week apart . Results : Distance covered increased significantly from a mean of 653 ( 61 ) m in the individual male tests to 735 ( 79 ) m in the male group tests ( p<0.05 ) , and 616 ( 75 ) m in the individual female tests to 701 ( 54 ) m in the female group tests ( p<0.01 ) . The men increased the distance walked in six minutes by 12.5 % and the women by 13.7 % when they performed the test as a group . Conclusion : Performing the six minute walk test in a group facilitates its execution As part of the Harvard Cancer Prevention Program Project , we used a social context ual model of health behavior change to test an intervention targeting multiple risk-related behaviors in working-class , multiethnic population s. We examined the relationships between the social context ual factors in our conceptual model and changes in fruit and vegetable consumption from baseline to completion of intervention in health centers and small business studies . We analyzed change in fruit and vegetable consumption , measured at baseline and final assessment s by self-report , in 2 r and omized controlled prevention trials : 1 in small businesses ( n = 974 ) and 1 in health centers ( n = 1954 ) .  Stronger social networks , social norms that were more supportive , food sufficiency , and less household crowding were associated with greater change in fruit and vegetable intake . We also observed differences between our intervention sites . Social context can play an important role in promoting changes in fruit and vegetable consumption Systematic review s that include nonr and omized studies ( NRS ) face a number of logistical challenges . However , the greatest threat to the validity of such review s arises from the differing susceptibility of r and omized controlled trials ( RCTs ) and NRS to selection bias . Groups compared in NRS are unlikely to be balanced because of the reasons leading study participants to adopt different health behaviours or to be treated differentially . Research ers can try to minimize the susceptibility of NRS to selection bias both at the design stage , for example , by matching participants on key prognostic factors , and during data analysis , for example , by regression modelling . However , because of logistical difficulties in matching , imperfect knowledge about the relationships between prognostic factors and between prognostic factors and outcome , and measurement limitations , it is inevitable that estimates of effect size derived from NRS will be confounded to some extent . Research ers , review ers and users of evidence alike need to be aware of the consequences of residual confounding . In poor quality RCTs , selection bias tends to favour the new treatment being evaluated . Selection bias need not necessarily lead to systematic bias in favour of one treatment but , even if it acts in an unpredictable way , it will still give rise to additional , nonstatistical uncertainty bias around the estimate of effect size . Systematic review s of NRS studies run the risk of compounding these biases . Nutritional choices and uptake of health education about nutrition are very likely to be associated with potential confounding factors . Therefore , pooled estimates of the effects of nutritional exposures and their confidence intervals are likely to be misleading ; review ers need to take into account both systematic and uncertainty bias OBJECTIVE The effects of positive- and negative peer modelling on  children 's consumption of a novel blue food  , presented in each of four snack meals during an " activity " day , were evaluated . It was predicted that : ( i ) novel food consumption would increase after positive modelling , but decrease after negative modelling ; ( ii ) modelling effects would generalise to a second novel blue food when participants were alone when they ate their snack ; ( iii ) that positive modelling would reverse the effects of negative modelling . DESIGN A mixed design was employed with r and om assignment to either Groups A , B , or C ( equal numbers of males and females per group ) . Within groups , each participant received the novel food on four snack occasions . Group A received positive modelling of blue food consumption on the first and third occasions , but were alone when they received the foods on the second and fourth occasions ; Group B had negative modelling on the first occasion , positive modelling on the third , and ate alone on the second and fourth ; Group C ate alone on all four occasions . To measure generalisation , an additional blue food was presented in all second and fourth " alone " occasions . PARTICIPANTS Thirty-five 5 - 7-year olds took part in Study 1 , and 44 3 - 4-year olds in Study 2 . RESULTS All main predictions were confirmed except that positive peer modelling did not reverse the effects of negative  modelling  in the 3 - 4-year olds . CONCLUSION Negative peer modelling inhibits novel food consumption , and its effects are particularly difficult to reverse in younger children Dietary patterns are useful in nutritional epidemiology , providing a comprehensive alternative to the traditional approach based on single nutrients . The Cardiovascular Risk in Young Finns Study is a prospect i ve cohort study with a 21-year follow-up . At baseline , detailed quantitative information on subjects ' food consumption was obtained using a  48 h dietary recall method ( n 1768 , aged 3 - 18 years ) . The interviews were repeated after 6 and 21 years ( n 1200 and n 1037 , respectively ) . We conducted a principal component analysis to identify major dietary patterns at each study point . A set of two similar patterns was recognised throughout the study . Pattern 1 was positively correlated with consumption of traditional Finnish foods , such as rye , potatoes , milk , butter , sausages and coffee , and negatively correlated with fruit , berries and dairy products other than milk .  Pattern 1 type of diet was more common among male subjects , smokers and those living in rural areas . Pattern 2 , predominant among female subjects , non-smokers and in urban areas , was characterised by more health-conscious food choices such as vegetables , legumes and nuts , tea , rye , cheese and other dairy products , and also by consumption of alcoholic beverages . Tracking of the pattern scores was observed , particularly among subjects who were adolescents at baseline . Of those originally belonging to the uppermost quintile of pattern 1 and 2 scores , 41 and 38 % respectively , persisted in the same quintile 21 years later . Our results suggest that food behaviour and concrete food choices are established already in childhood or adolescence and may significantly track into adulthood This study investigates the effects of peer influence on the food intake of overweight and normal-weight children . A mixed factorial design was employed , with children 's weight status ( overweight vs. normal-weight ) as a between-subjects factor , and social context ( alone vs. group ) as a within-subjects factor . A total of 32 children ( n=17 overweight and n=15 normal-weight ) between the ages of 6 - 10 years participated in this study . Findings from the r and om regression model indicated that overweight children ate more when with others than when alone , while in contrast normal-weight ate more with others than they did when alone . Therefore , social context differentially impacts the eating behavior of overweight and normal-weight children . This study underscores differences in responses to the social environment between overweight and non-overweight youths , and suggests that social involvement may be an important tool in treatment and prevention programs for overweight and obesity PURPOSE The aim of the study was to investigate the  tracking of physical activity ( PA )  from preschool age to adulthood in six age cohorts of males and females . METHODS A r and om sample of 3596 boys and girls age 3 - 18 yr participated in the Cardiovascular Risks in Young Finns Study in 1980 . The follow-up measurements were repeated in 1986 , 1992 , 2001 , and 2007 . The  PA  was measured by mother 's report in 3- and 6-yr-olds and self-report in 9-yr-olds and older .  Tracking of PA  was analyzed using the Spearman rank-order correlation and a simplex model . RESULTS Mother-reported PA at age 3 and 6 yr significantly predicted self-reported PA in youth and in young adulthood , and there was a significant indirect effect of mother report on adult PA 2007 in males . Simplex models that fitted the data very well produced higher stability coefficients than the Spearman rank-order correlations showing moderate or high tracking . The tracking was higher in males than that in females . CONCLUSION This study has shown that physically active lifestyle starts to develop very early in childhood and that the stability of PA is moderate or high along the life course from youth to adulthood Although Social Cognitive Theory ( B and ura , 1997 ) suggests that teacher modeling would be one of the most effective methods to encourage food acceptance by preschool children , opinions of experienced teachers have not yet been sample d , teacher modeling has rarely been examined experimentally , and it has produced inconsistent results . The present study considers opinions of teachers and conditions under which teacher modeling is effective . Study 1 was a question naire in which preschool teachers ( N=58 ) were found to rate modeling as the most effective of five teacher actions to encourage  children 's  food acceptance . Study 2 and Study 3 were quasi-experiments that found silent teacher modeling ineffective to encourage either familiar food acceptance ( N=34 ; 18 boys , 16 girls ) or new food acceptance ( N=23 ; 13 boys , 10 girls ) . Children 's new food acceptance was greatest in the first meal and then rapidly dropped , suggesting a " novelty response " rather than the expected neophobia . No gender differences were found in response to silent teacher modeling . Study 4 was a repeated- measures quasi-experiment that found enthusiastic  teacher modeling ( " Mmm ! I love mangos ! " ) could maintain new food acceptance across five meals , again with no gender differences in response to teacher modeling ( N=26 ; 12 boys , 14 girls ) . Study 5 found that with the addition of a competing peer model , however , even enthusiastic  teacher modeling was no longer effective to encourage new food acceptance and gender differences appeared , with girls more responsive to the peer model ( N=14 ; 6 boys , 8 girls ) . Thus , to encourage children 's new food acceptance , present results suggest that teachers provide enthusiastic modeling rather than silent modeling , apply such enthusiastic modeling during the first five meals before children 's " novelty response " to new foods drops , and avoid placing competing peer models at the same table with picky eaters , especially girls The purpose of this research was to compare the self-images of male and female children in order to determine whether females were at a particular disadvantage and , if so , why . A r and om sample of 1988 children from grade s 3–12 were interviewed in Baltimore in 1968 . Findings show more disturbance among White adolescent females than among White males or Black females : White girls become much more self-conscious and show greater self-image instability and somewhat lower self-esteem . Three sets of factors appear to explain part of these differences : ( 1 ) attitudes toward present and future sex role , ( 2 ) peer relationships in general and opposite sex relationships in particular , and ( 3 ) attitudes toward changing looks in adolescence The Scottish Intercollegiate Guidelines Network ( SIGN ) develops evidence based clinical guidelines for the NHS in Scotl and . The key elements of the methodology are ( a ) that guidelines are developed by multidisciplinary groups ; ( b ) they are based on a systematic review of the scientific evidence ; and ( c ) recommendations are explicitly linked to the supporting evidence and grade d according to the strength of that evidence . Until recently , the system for grading guideline recommendations was based on the work of the US Agency for Healthcare Research and Quality ( formerly the Agency for Health Care Policy and Research ) . 1 2 However , experience over more than five years of guideline development led to a growing awareness of this system 's weaknesses . Firstly , the grading system was design ed largely for application to questions of effectiveness , where r and omised controlled trials are accepted as the most robust study design with the least risk of bias in the results . However , in many areas of medical practice r and omised trials may not be practical or ethical to undertake ; and for many questions other types of study design may provide the best evidence . Secondly , guideline development groups often fail to take adequate account of the method ological quality of individual studies and the overall picture presented by a body of evidence rather than individual studies or they fail to apply sufficient judgment to the overall strength of the evidence base and its applicability to the 
    Output:
    
Conclusions Although supported by weak evidence , peers appear to influence children ’s  eating behaviors and physical activity .
However , this influence may be moderated by the number of peers , gender , age and the perceived status of the role models .