Background: The New York Longitudinal Study (NYLS) identified three core temperament types—Easy, Difficult, and Slow-to-warm-up—based on early qualitative analyses of childhood behavior and constrained by the analytic tools available at the time. However, more than one-third of participants could not be classified within this framework, and the typology has never been formally revised using contemporary statistical approaches, which limits the model’s generalizability. Despite these methodological constraints, the nine NYLS temperament dimensions and their associated typology have remained influential in both research and applied contexts. Methods: This study revisited the NYLS framework using latent profile analysis (LPA), a probabilistic person-centered method that identifies latent subgroups based on multivariate response patterns. Data were drawn from a large adult sample assessed with the standardized Chess–Thomas Adult Temperament Questionnaire, second edition (ATQ2), as well as its newly validated Lithuanian version. The sample comprised 1260 adults aged 18–80 years (M = 32.2) from the USA (n = 554) and Lithuania (n = 706). To enhance robustness and cross-group comparability, measurement invariance (MI) was tested across country, gender, and age groups. Results: A five-profile solution emerged as optimal. Three profiles resembled the classic NYLS types—Easy (13.1%), Difficult (11.1%), and Slow-to-warm-up (13.5%)—and two additional profiles were identified: Curious (33.3%) and Shy (29.0%). The new profiles reflected coherent behavioral patterns centered on approach-withdrawal tendencies and activity level, demonstrated conceptual convergence with other temperament and personality typologies, and remained consistent across demographic groups. Conclusions: These findings refine and expand the original NYLS typology with greater methodological rigor, providing a statistically validated framework for understanding adult temperament that can inform future developmental research, psychological assessment, and clinical practice.
McDevitt et al. (Tue,) studied this question.