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Table 4 Sample size calculations to assess intervention impact on primary and secondary outcomes

From: Comparison of two forms of daily preventive zinc supplementation versus therapeutic zinc supplementation for diarrhea on young children’s physical growth and risk of infection: study design and rationale for a randomized controlled trial

Variable Detectable difference βa Unadjusted sample size per treatment group Attrition Adjusted sample size per treatment groupb Total sample size, four treatment groups
Primary outcomes
Length and length-for-age-Z-score 0.20 SD 0.10 710 15% 850 3400
Weight and weight-for-age-Z-score 0.20 SD 0.10 710 15% 850 3400
Incidence of diarrhea 0.20 SD 0.10 710 15% 850 3400
Biochemical indicators of micronutrient statusc 0.40 SD 0.20 133 30% 190 760
Indicators of innate and adaptive immune response 0.50 SD 0.20 88 30% 125 500
Secondary outcomes
Intestinal parasite burden 0.30 SD 0.20 244 20% 305 1220
Indicators of environmental enteric dysfunction 0.35 SD 0.20 179 20% 225 900
Hair cortisol 0.40 SD 0.20 133 30% 190 760
  1. aPower used for sample size calculation with a significance of α = 0.05
  2. bAdjusted for attrition and rounded up
  3. cHemoglobin concentration was used as a screening criteria for study enrollment; thus the hemoglobin concentration of all children enrolled in the study was assessed and sample size calculations were not completed for this primary outcome