ABSTRACT
BACKGROUND: Very little research exists that looks at the Ages and Stages Questionnaire simultaneously from a modern latent variable point of view and by looking at its psychometric properties over time. AIMS: To explore the latent factor structure of the ASQ using Exploratory Structural Equation Modeling techniques for ordinal data and investigate its change over time using the method of vertical scaling from multidimensional Item Response Theory. STUDY DESIGN: Longitudinal, with the same children being assessed at multiple timepoints. SUBJECTS: Children measured using the 12, 14, 16, 18, 20, 22, 24, 27, 30, 33, 36, 42, 48month questionnaires of the ASQ. Initial sample (12months) consisted of 2219 children and final sample (48months), 892 children due to drop-out. OUTCOME MEASURES: Ages and Stages Questionnaire, 3rd version (ASQ-3). RESULTS: Results indicate that all ASQ-3 age questionnaires examined showed the proposed 5-factor structure (except the 12-month version) but with different patterns over time. The Gross Motor domain had the fewest misfitting items, from 12months onwards. The Personal-Social domain and the Problem Solving domain had larger numbers of misfitting items. Results from the vertical scaling analysis showed that both the Problem-Solving and Personal-Social dimensions also exhibited the most complex patterns of change over time. CONCLUSIONS: The psychometric properties of the ASQ-3 seem to be both time-dependent and domain-dependent. Earlier questionnaires reflect a latent structure that was not as well-defined as for later versions. Also, domains such as Communication and Gross Motor appear to be much more reliably measured than others, such as Problem-Solving and Personal-Social.