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Do larger studies find smaller effects? The example of studies for the prevention of conduct disorder

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Abstract

Introduction

There is some emerging evidence in medicine that larger clinical trials tend to be associated with smaller effect sizes. Much of the evidence-base currently informing practice in Child Psychiatry relies on relatively small trials. We therefore investigated the relationship between trial size and effect size in research within a key area of child mental health.

Method

A recent systematic review of 20 trials of prevention of conduct disorder was subjected to meta-regression, to examine the relationship between study size and effect size, and to explore hypothesised confounding variables.

Results

In this sample of studies, reported effect size was inversely related to sample size. This effect is not explained by year of publication, intervention type or quality of methodology in the study.

Discussion

Our finding is consistent with other reports in the literature. The origin of this effect is not yet clear. However if replicated it clearly has significant implications for the way trials in child mental health are interpreted.

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Author information

Authors and Affiliations

  1. Thorn Road Clinic, Thorn Road, Runcorn, Cheshire, WA7 5HQ, UK

    Brid McMahon

  2. Springleigh Clinic, Waterloo Road, Stalybridge, SK15 2AU, UK

    Louise Holly

  3. Division of Psychiatry, University of Manchester, Manchester, M13 9PT, UK

    Richard Harrington

  4. Bio-Statistics Group, School of Epidemiology and Health Sciences, University of Manchester, Manchester, M13 9PT, UK

    Chris Roberts

  5. Psychiatry Research Group, Room 4.319, University Place, University of Manchester, Oxford Road, Manchester , M13 9PL, UK

    Jonathan Green (Prof.)

Authors
  1. Brid McMahon
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  2. Louise Holly
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  3. Richard Harrington
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  4. Chris Roberts
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  5. Jonathan Green
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Corresponding author

Correspondence to Jonathan Green.

Additional information

Richard Harrington: Diseased

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McMahon, B., Holly, L., Harrington, R. et al. Do larger studies find smaller effects? The example of studies for the prevention of conduct disorder. Eur Child Adolesc Psychiatry 17, 432–437 (2008). https://doi.org/10.1007/s00787-008-0685-9

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  • DOI: https://doi.org/10.1007/s00787-008-0685-9

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