Sample attrition bias in a longitudinal study of young people

Attrition analyses are reported from a longitudinal survey of young people conducted annually over the years 1980–1988. Not surprisingly, there was considerable sample attrition over the period so that the initial sample of 3,130 was reduced to 483 after eight years. This reflected an average annual retention rate of just under 80%. There was evidence of some selective bias in attrition, particularly during the early years, when those dropping out tended to be of lower academic ability, lower socioeconomic status, and from non‐English backgrounds. Although most of the differences were slight, the drop‐outs also exhibited greater externality of locus of control and less achievement motivation than those who stayed in, as well as being greater consumers of alcohol, cigarettes, and both non‐prescribed and illicit drugs. These results are similar to those that have been reported from other comparable studies conducted in the United States. Implications for the interpretation of longitudinal survey data are discussed.