Boreham, C.A.

Lenthe, F.J. (Frank) van

Murray, L.

Savage, M.J.

Smith, G.D.

Twisk, J.W.R. (Jos)

Erasmus University Digital Repository

doi:10.1136/jech.55.9.681  2001;55;681-682 J. Epidemiol. Community Health  Smith F J van Lenthe, C A Boreham, J W R Twisk, M J Savage, L Murray and G Davey   and young adulthood: the Young Hearts Studycoronary heart disease risk factors between youth What determines drop out in prospective studies of http://jech.bmj.com/cgi/content/full/55/9/681Updated information and services can be found at:  These include: References http://jech.bmj.com/cgi/content/full/55/9/681#otherarticles1 online articles that cite this article can be accessed at:    http://jech.bmj.com/cgi/content/full/55/9/681#BIBLThis article cites 3 articles, 2 of which can be accessed free at: Rapid responses http://jech.bmj.com/cgi/eletter-submit/55/9/681You can respond to this article at:  serviceEmail alertingtop right corner of the article Receive free email alerts when new articles cite this article - sign up in the box at the Notes    http://www.bmjjournals.com/cgi/reprintformTo order reprints of this article go to:  http://www.bmjjournals.com/subscriptions/ go to: Journal of Epidemiology and Community HealthTo subscribe to  on 21 November 2006 jech.bmj.comDownloaded from What determines drop out in prospective studiesof coronary heart disease risk factors betweenyouth and young adulthood: the Young HeartsStudyF J van Lenthe, C A Boreham, J W R Twisk, M J Savage, L Murray, G Davey SmithThe growing recognition of the importance ofearly life factors in the development ofcoronary heart disease (CHD) may increaseprospective research in this period of life. Froma methodological point of view, drop out ofsubjects, particularly when this is selective, is amajor threat to the validity of the results. Spe-cific information about determinants of dropout in current studies may therefore yieldimportant information for future studies. Wehave analysed risk of drop out in the YoungHearts Project, a prospective study in North-ern Ireland.1Methods and ResultsThe Young Hearts Project is a prospectivecohort study, which started in two cohorts of12 year old boys (n=251) and girls (n=258)and 15 year old boys (n=252) and girls(n=254) in Northern Ireland (overall responserate 78%) in 1988. Its aim and design havebeen described elsewhere in detail.1 In 1992/93these children were re-examined under identi-cal conditions. In 1997 the third wave of datacollection was carried out in participants meanage 21 years (cohort 1) and 24 years (cohort 2).In cohort 1 and 2 data were obtained from49.9% (boys: n=135; girls: n=119) and 46.4%(boys: n=116; girls: n=119) respectively of thesubjects included at baseline. We created adichotomous variable thereby distinguishingthose at baseline who were still in the studynine years later from those who were in thestudy initially but who dropped out of thestudy. Logistic regression analysis was carriedout to investigate if less then good perceivedgeneral health, sociodemographic (sex andsocioeconomic position), biological (birthweight, body height, body weight, sum of fourskinfolds, systolic and diastolic blood pressure,total serum cholesterol, high density lipopro-teins and cardiorespiratory fitness (measuredby the 20 metre shuttle run test) andbehavioural (physical inactivity, total energyintake, and intake of fat, cholesterol, fruit andvegetable) risk indicators of coronary heartdisease at baseline were associated with risk ofdrop out. Indicators univariately associatedwith risk of drop out (p< 0.20) were entered ina multivariate analyses; final models werederived using a backward elimination proce-dure.Table 1 presents the univariate and multi-variate associations for the final models.Consistent findings in both cohorts are the sig-nificantly increased odds ratio for those in themanual compared with the non-manualgroups. Odds ratios of drop out increased byincreasing sum of skinfolds (in cohort 1) andincreasing systolic blood pressure (in cohort 2).In both cohorts risk of drop out was associatedwith birth weight; however, an increased oddsratio was found in subjects in the lower tertileof birth weight in cohort 1 and the upper tertileTable 1 Determinants of drop out in the Young Hearts Project between the first (1988) and third (1997) wave of datacollection in boys and girls 12 and 15 years of age at baselineNumberUnivariate MultivariateOdds ratio (95% CI) p Odds ratio (95% CI) pCohort 1 (12 years at baseline)Socioeconomic position 0.00 0.00Non-manual 280 1.00 1.00Manual 178 1.97 (1.35, 2.88) 1.93 (1.31, 2.84)Missing 51 3.79 (1.96, 7.32) 3.78 (1.93, 7.37)Birth weight (100 g) 0.01 0.03Normal 156 1.00 1.00Low (<3118 g)* 155 1.22 (0.78, 1.90) 1.12 (0.70, 1.77)High (>3540 g) 154 0.62 (0.40, 0.98) 0.62 (0.39, 0.99)Missing 44 1.51 (0.76, 2.99) 1.45 (0.72, 2.91)Sum of skinfolds (cm) 509 1.12 (1.02, 1.23) 0.02 1.13 (1.02, 1.25) 0.02Cohort 2 (15 years at baseline)Socioeconomic position 0.01 0.02Non-manual 253 1.00 1.00Manual 189 1.79 (1.22, 2.62) 1.75 (1.18, 2.60)Missing 64 1.45 (0.83, 2.51) 1.28 (0.72, 2.26)Birth weight (100 g) 0.06 0.01Normal 155 1.00 1.00Low (<3180 g)* 157 1.33 (0.85, 2.07) 1.21 (0.76, 1.92)High (>3629 g) 154 1.80 (1.15, 2.83) 2.12 (1.32, 3.41)Missing 40 1.77 (0.88, 3.60) 2.18 (1.05, 4.52)Body height (cm) 506 0.98 (0.96, 1.00) 0.11 0.97 (0.94, 0.99) 0.05Systolic blood pressure (10 mm Hg) 506 1.29 (1.11, 1.49) 0.00 1.36 (1.16, 1.59) 0.00*Values based on tertiles, with missing values included as a separate group.J Epidemiol Community Health 2001;55:681–682 681Department of PublicHealth, ErasmusUniversity Rotterdam,PO Box 1738, 3000 DRRotterdam, theNetherlandsF J van LentheApplied MedicalSciences and SportsStudies, University ofUlster, NorthernIrelandC A BorehamInstitute for Researchin ExtramuralMedicine, VrijeUniversiteitAmsterdam, theNetherlandsJ W R TwiskDepartment of ChildHealth, Institute ofClinical Sciences,Royal VictoriaHospital, Belfast,Northern IrelandM J SavageDepartment ofEpidemiology andPublic Health, Queen’sUniversity of Belfast,Northern IrelandL MurrayDepartment of SocialMedicine, Universityof Bristol, UnitedKingdomG Davey SmithCorrespondence to:Dr van Lenthe(vanlenthe@mgz.fgg.eur.nl)Accepted for publication16 March 2001www.jech.com on 21 November 2006 jech.bmj.comDownloaded from in cohort 2. There seemed to no statisticallysignificantly associations between behaviouralrisk indicators of coronary heart disease andrisk of drop out.CommentsWe described the profile of children atincreased risk of drop out. Clearly, there is noinformation as to whether these children stillhave the same risk profile in young adulthood.Tracking studies however predict a relative sta-bility in risk factors in age and sex specificpopulations over time.2 Hence, there arereasons to expect that those who dropped outof the study are likely to show the same riskprofile in young adulthood as they did in child-hood.In non-response research refusal, illness andhaving moved to another school were given asmain reasons for drop out between the first andsecond period of measurement.3 Unfortu-nately, no such information is available be-tween the second and third wave of datacollection.In our study, socioeconomic position seemedto be a main determinant of drop out. Interest-ingly, there is increasing awareness of the needto study socioeconomic inequalities in coron-ary heart disease from a life course perspec-tive.4 Our findings suggest that socioeconomicinequalities in coronary heart disease risk indi-cators in early life may be underestimated as aconsequence of selective drop out by socioeco-nomic position (and some coronary heartdisease risk indicators). While further investi-gating the life course perspective, researchersneed to pay particular attention to those inlower socioeconomic groups with respect toadherence to the study.Funding: this study is financially supported by the NorthernIreland Chest, Heart and Stroke Association, the British HeartFoundation and Wellcome Trust.Conflicts of interest: none.1 Boreham C, Savage JM, Primrose D, et al. Coronary riskfactors in schoolchildren. Arch Dis Child 1993;68:182–6.2 Twisk JWR,Kemper HCG,Mechelen W van, et al. Trackingof risk factors for coronary heart disease over a 14-yearperiod: a comparison between lifestyle and biologic riskfactors with data from the Amsterdam Growth and HealthStudy. Am J Epidemiol 1997;145:888–98.3 Twisk JWR, Boreham C, Cran G, et al. Clustering ofbiological risk factors for cardiovascular disease and thelongitudinal relationship with lifestyle of an adolescentpopulation: The Northern Ireland Young Hearts Project. JCardiovasc Risk 1999;6:355–62.4 Davey Smith G, Hart C, Gilles C, et al. Lifetimesocioeconomic position and mortality: prospective obser-vational study. BMJ 1997;314:547–52.Browse the Archivewww.jech.comWith a single click Collections allows you to find all articles that have been published in yourchosen subject. Select from over 200 clinical and non-clinical topic collections and/or cross search otherspecialist journals, the BMJ and Cochrane ReviewsCollectionsBrowsing made easy682 van Lenthe, Boreham, Twisk, et alwww.jech.com on 21 November 2006 jech.bmj.comDownloaded from 

What determines drop out in prospective studies of coronary heart disease risk factors between youth and young adulthood: the Young Hearts Study

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What determines drop out in prospective studies of coronary heart disease risk factors between youth and young adulthood: the Young Hearts Study

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