Who and how: some unanswered questions in adult development.

This study argues that a better understanding of the processes of life span and adult development can be reached if there is a distinction made between the concepts of stability and continuity. The latter implies both stability and change. To assess continuity, a model of personality development must be adopted that covers both general and differential aspects of its course during the life span. This makes it possible to identify and assess individual variations or types of individual development, as well as general developmental trends. Because statements about stability and continuity are inevitably contingent upon techniques of data collection and statistical methods, it is recommended that research designs should be used that permit comparison of normative and ipsative approaches to the same population. To illustrate and support this argument, the design and rationale of the Jerusalem Study of Psychological Development during Middle and Later Adulthood are briefly described, as well as the resulting personality types and their development as empirically identified by application of Q-technique.