ABSTRACT
In a long-standing longitudinal study, it is natural that all data cannot be collected from all members of the initial sample. It is important to analyze whether the attrition, that is, the reduction in the number of participants, had been selective and had therefore affected the representativeness of the sample. The analysis of the attrition and the representativeness of the sample showed that the sample studied in middle age was a good representation of the initial random sample, and the distributions of demographic variables corresponded with those in the age cohort group born in 1959 in Finland. At the time when the JYLS was started, the development of the technique of factor analysis inspired personality researchers to examine dimensions of variables (e.g., extraversion) in which differences between individuals can be described. This approach is called variable-oriented. In the JYLS, the person-oriented approach has also been applied in data analysis, particularly for finding different personality types and profiles.
