Valid and reliable life-course and cross-cohort comparisons of psychological distress are limited by differences in measures used. We aimed to examine adulthood distribution of symptoms and cross-cohort trends by equating the scales of psychological-distress measures administered in the 1946, 1958, and 1970 British birth cohorts. We used data from these three birth cohorts (N = 32,242) and an independently recruited calibration sample (n = 5,800) to inform the equating of scales. We used two approaches to equating scales (equipercentile linking and multiple imputation) and two index measures (General Health Questionnaire-12 and Malaise-9) to compare means, distributions, and prevalence of distress across adulthood. Although we consistently observed an inverse U shape of distress across adulthood, we also observed measure and method differences in point estimates, particularly for cross-cohort comparisons. Sensitivity analysis suggested that multiple imputation yielded more accurate estimates than equipercentile linking. Although we observed an inverse-U-shaped trajectory of psychological distress across adulthood, differences in point estimates between measures and methods did not allow for clear conclusions regarding between-cohorts trends
