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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Abstract
The Young Hearts Project is a prospective cohort study, which started in two cohorts of 12 year old boys (n=251) and girls (n=258) and 15 year old boys (n=252) and girls (n=254) in Northern Ireland (overall response rate 78%) in 1988. Its aim and design have been described elsewhere in detail.1 In 1992/93 these children were re-examined under identical conditions. In 1997 the third wave of data collection was carried out in participants mean age 21 years (cohort 1) and 24 years (cohort 2). In cohort 1 and 2 data were obtained from 49.9% (boys: n=135; girls: n=119) and 46.4% (boys: n=116; girls: n=119) respectively of the subjects included at baseline. We created a dichotomous variable thereby distinguishing those at baseline who were still in the study nine years later from those who were in the study initially but who dropped out of the study. Logistic regression analysis was carried out to investigate if less then good perceived general health, sociodemographic (sex and socioeconomic position), biological (birth weight, body height, body weight, sum of four skinfolds, systolic and diastolic blood pressure, total serum cholesterol, high density lipoproteins and cardiorespiratory fitness (measured by the 20 metre shuttle run test) and behavioural (physical inactivity, total energy intake, and intake of fat, cholesterol, fruit and vegetable) risk indicators of coronary heart disease at baseline were associated with risk of drop out. Indicators univariately associated with risk of drop out (p< 0.20) were entered in a multivariate analyses; final models were derived using a backward elimination procedure.