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Comment & Response
January 2015

Problematic Consequences of Using Standard Errors Rather Than Standard Deviations: Calculation of Effect Sizes

Author Affiliations
  • 1Institute for Health Research and Policy, University of Illinois at Chicago, Chicago
JAMA Pediatr. 2015;169(1):95. doi:10.1001/jamapediatrics.2014.2986

To the Editor In the article recently published in JAMA Pediatrics on a cluster randomized trial of the Healthy Buddies program, Santos and colleagues1 reported effect sizes for the impact of intervention on the assessed outcomes, with waist circumference and body mass index z scores serving as primary outcomes. The formula given for calculating each effect size was the difference between treatment and control groups in baseline to follow-up differences on the outcome measure divided by the pooled standard error of the measure. The use of a measure’s standard error for calculating an effect size is problematic for at least 2 reasons.

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