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

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

Variable	Detectable difference	β^a	Unadjusted sample size per treatment group	Attrition	Adjusted sample size per treatment group^b	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 status^c	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

^aPower used for sample size calculation with a significance of α = 0.05
^bAdjusted for attrition and rounded up
^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