Psychological distress across adulthood: scale-equating in three British birth cohorts

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 scale-equating 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 scale-equating. We used two approaches to scale-equating (equipercentile linking and multiple imputation) and two index-measures (General Health Questionnaire [GHQ]-12 and Malaise-9) to compare means, distributions and prevalence of distress across adulthood. While 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. Though 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-cohort trends.