The ability to quantify within-person changes in mental health is central to the mission of clinical psychology. Typically, this is done using total or mean scores on symptom measures; however, this approach assumes that measures quantify the same construct, the same way, each time the measure is completed. Without this quality, termed longitudinal measurement invariance, an observed difference between timepoints might be partially attributable to changing measurement properties rather than changes in comparable symptom measurements. This concern is amplified in research using different forms of a measure across developmental periods due to potential differences in reporting styles, item-wording, and developmental context. This study provides the strongest support for the longitudinal measurement invariance of the Anxiety Scale, Depression/Affective Problems: Cognitive Subscale, and the Attention Deficit Hyperactivity Disorder (ADHD) Scale; moderate support for the Depression/Affective Problems Scale and the Somatic Scale, and poor support for the Depression/Affective Problems: Somatic Symptoms Subscale of the Dutch Achenbach System of Empirically Based Assessment Youth Self-Report and Adult Self-Report in a sample of 1,309 individuals (N = 1,090 population-based, N = 219 clinic-based/referred to an outpatient clinic before age 11 years) across six waves of data (mean ages = 11 years at Wave 1 and 26 years at Wave 6).
Keywords: adolescent; adult; developmental; longitudinal; measurement; measurement invariance; psychopathology.