Potential dropouts in a longitudinal study: Prevalence,stability, and associated characteristics

This study quantifies the prevalence and associated characteristics of subjects in a longitudinal study who are difficult to schedule and thus may become potential study dropouts. Although subject attrition over three years remained extremely low, many families were difficult to schedule for their assessments and this remained rather constant over time. Intercorrelations between the measures of scheduling difficulty were high, indicating good internal validity of the constructs. Stability of these measures from year to year was low, making it difficult to predict which families required more staff effort or were at risk for dropping out of the study in any one year. Race appeared to be associated with several measures of scheduling difficulty, while psychiatric characteristics of the sample were less so.