Table 2

Summary of assumed intervention effects, clustering and power for primary and secondary outcomes

OutcomeIntervention vs ControlCV*ICC*Assumed n per clusterPower
 Proportion of fevers with test§70% vs 31%0.400.0734098%
 Proportion of ACT taken by those who test positive§72.5% vs 36.5%0.17**0.017**10>99%
 Proportion of ACT taken by those with no test§16.9% vs 56.6%0.220.06410>99%
 Proportion who take ACT after a positive test§90% vs 70%0.04**0.003**5NA††
 Proportion who take ACT after a negative test§10% vs 10%0.250.0077NA††
  • Values in each arm are calculated using the assumed probabilities from pilot data (shown on the branches of figure 3) where 37.4% of intervention and 25.6% of control arm participants are estimated to take ACTs.

  • *Clustering estimated using methods suggested by Hayes and Moulton (2009).23 Details for CV presented in the text with ICC estimated using ICC=CV2×π/(1-π), where π is the assumed control-arm proportion for the outcome.

  • Set at the minimum of n per intervention arm cluster and n per control arm cluster, derived using assumed probabilities in figure 3 and based on 40 fevers per cluster.

  • Power at each of 3 follow-up time points for a cluster-randomised trial of 16 control CUs vs 16 intervention CUs at an overall 5% type-1 error rate for each outcome with Bonferroni correction for 3 time points.

  • §Assumptions based on pilot data as listed on the branches of figure 3.

  • **Values differ from the IRB protocol because a plausible range of values for the control arm used updated pilot data.

  • ††Not applicable (NA) since assumed to be equal in both arms.

  • ACT, artemisinin combination therapy; CU, community units; CV, coefficient of variation; ICC, intraclass correlation coefficient; IRB, Institutional Review Board.