ABSTRACT
The importance of the work of Alex Thomas and Stella Chess lies in its under-standing of the evolution of child-environment interaction. Outcome for children appears to emerge from the dynamic interplay between parent and child and between child and environment, and in the multiple experiences that occur from before birth onward. The richness and complexity in the volumes that emanated from the New York Longitudinal Study (NYLS), starting with Behavioral Individuality in Early Childhood (Thomas, Chess, Birch, Hertzig, & Korn, 1963), convinced many child development researchers and clinicians that this seminal contribution ought to be followed by confirmation and validation of the NYLS findings by further empirical research. Because the NYLS was a pioneering anterospective effort, much of its quantitative and methodological decision making admittedly was based on improvisation and intuition rather than on detached, calculated proven research strategies. Even with the limitations inherent in research design, the import of the NYLS findings demanded replication and validation. Certainly the essence of what the NYLS team was observing and recording could be reduced to objective, empirically based fact!
