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CLOSER report sheds new light on harmonising longitudinal measures of mental health

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Woman sitting on a hill looking out over a view of fields and woodsA new CLOSER report documenting the reliability and measurement equivalence of mental health questionnaires within and across six British cohort studies has been published today.

This report is designed to help researchers understand the measurement properties and maximise the comparability of existing mental health measures within and across the cohort studies.

Led by Prof George B. Ploubidis (UCL Centre for Longitudinal Studies (CLS)), the new resource provides an overview of the authors’ comprehensive investigation into the psychometric properties and measurement equivalence of the mental health measures available in the following longitudinal studies:

  • MRC 1946 National Survey of Health and Development
  • 1958 National Child Development Study
  • 1970 British Cohort Study
  • Avon Longitudinal Study of Parents and Children
  • Next Steps (formerly the Longitudinal Study of Young People in England)
  • Millennium Cohort Study

To investigate the comparability of mental health measures, the authors tested the measurement equivalence of two questionnaires focussed on mental ill-health/psychological distress– the Malaise Inventory and the Strengths and Difficulties Questionnaire – conducted at different time points in four of the six longitudinal studies. Their findings suggest that valid comparisons can be made within and across cohorts when the same questionnaire has been used.

In instances where different questionnaires were used, either in different sweeps or in different cohorts, the authors used a content validation approach to identify questions that assessed the same underlying symptom(s). This information was subsequently used to produce a searchable tool designed to enable researchers to identify harmonisable subsets of items from different questionnaires that can be used for both within-cohort and cross-cohort research.

Psychometric analyses of these harmonised subsets of items found they had favourable psychometric properties meaning they can be used to study changes over time, both within and across the studies.

The new insights offered by this report also serve as useful guidance more generally to researchers seeking to learn about the methodological considerations and approaches that can be drawn upon in integrating questionnaire data (in particular standardised measures) from different sources or time periods for comparative analysis.

Dr Eoin McElroy (University of Leicester), lead author of the report, states: “Our hope is that by helping researchers’ understanding of the measurement properties and comparability of existing mental health measures within and across these cohort studies, this will, in turn, facilitate more reliable and valid longitudinal and cross-study research.”

This report was produced as part of a CLOSER project which aims to harmonise existing mental health measures over the life course in six British cohort studies. The project was led by Prof George B. Ploubidis with support from Dr Eoin McElroy. They worked on this project in collaboration with Dr Praveetha Patalay (CLS and the MRC Unit for Lifelong Health and Ageing at UCL (MRC LHA)), Prof Marcus Richards (MRC LHA), Dr Kate Northstone (Bristol Medical School), as well as Prof Pasco Fearon and Dr Marc Tibber (UCL Department of Clinical, Health and Educational Psychology).


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