Anna Freud took as the starting point of her discussion Kris's 1950 paper 'Notes on the Development and Some Current Problems of Psychoanalytic Child Psychology', where the theoretical formulations of the 1920s were first shown to have opened up a new field in which observational studies of children could be integrated with reconstructive data to enlarge and enrich the total developmental picture. For this purpose Kris favoured above all the longitudinal study.

Newer technical and theoretical developments, especially the growing preoccupation with ego psychology, impressed Kris with the fluid and often chaotic state of our diagnostic categories, and he therefore worked to place fact-finding in observational research at the service of diagnosis. It became