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Multiple trials may yield exaggerated effect size estimates.

Andrew Brand1, Michael T Bradley, Lisa A Best

  • 1Department of Psychology, Kings College, London.

The Journal of General Psychology
|March 17, 2011
PubMed
Summary
This summary is machine-generated.

Researchers may overestimate effect sizes in psychological studies by using too many participants or trials. Increasing trials or items inflates estimates, though correlations can reduce this bias.

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Area of Science:

  • Psychology
  • Psychological Research Methods
  • Statistical Analysis

Background:

  • Psychological studies often struggle to detect small to medium effect sizes due to insufficient participant numbers.
  • Researchers may employ repeated trials or multiple items to achieve statistical significance.
  • This practice can potentially inflate observed effect size estimates.

Purpose of the Study:

  • To investigate the impact of increasing the number of trials or items on effect size estimates in psychological research.
  • To analyze how averaging and aggregating dependent measures across multiple trials/items affects observed effect sizes.
  • To understand the role of correlations between trials/items in mitigating overestimation.

Main Methods:

  • Utilized Monte-Carlo simulations to model the effects of repeated trials and multiple items.
  • Analyzed the impact on effect size estimates when dependent measures are averaged and aggregated.
  • Examined scenarios with varying degrees of correlation between trials or items.

Main Results:

  • Simulations demonstrated a substantial increase in observed effect size estimates with a higher number of trials or items.
  • The overestimation of effect sizes was partially mitigated by positive correlations between trials or items.
  • However, significant overestimation persisted even with correlations in some simulated cases.

Conclusions:

  • The aggregation of measures (e.g., P300 wave, test scores) can lead to inflated effect size estimates if not carefully handled.
  • Researchers, particularly in exploratory studies, must be cautious about the interrelations among trials/items to avoid biased results.
  • Methodological awareness regarding the impact of study design on effect size is crucial for accurate psychological research.