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Table 4 Power calculations: SHARE trials

From: The effectiveness and cost-effectiveness of the peer-delivered Thinking Healthy Programme for perinatal depression in Pakistan and India: the SHARE study protocol for randomised controlled trials

Assumptions Pakistan India
Unit of randomisation Villages (stratified within union councils) Individual (stratified by urban/rural area of residence)
Intra-cluster correlation 0.07 in the intervention arm 0.05 in the intervention arm (30 therapists; within-therapist clustering) [22, 32, 33]
0.05 in the control arm (between-village clustering) [22]
Loss to follow-up over 6 months 20 % [22] 15 % [8]
Allocation ratio (intervention/control) 1:1 1:1
Number of participants 560 (14 per village; 40 village clusters) 280
Outcome Power
Remission at 6 months (PHQ-9 < 10) of 65 % in the intervention arm vs 45 % in the control arm [22] 90 % 86 %
Remission at 6 months (PHQ-9 ≤ 5) of 38 % in the intervention arm vs 22 % in the control arm [22] 81 % 74 %
Depression severity at 6 months (PHQ-9 score) – effect size 0.4 90 % 84 %