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Table 2 Sample size estimates derived from the first complete round of enrolment and follow-up visit of RECAMP-MV and RECAMP-OPV

From: Research protocol of two concurrent cluster-randomized trials: Real-life Effect of a CAMPaign with Measles Vaccination (RECAMP-MV) and Real-life Effect of a CAMPaign with Oral Polio Vaccination (RECAMP-OPV) on mortality and morbidity among children in rural Guinea-Bissau

RECAMPMVOPV
Number of clusters222
Alpha0.05
Between cluster variation coefficient0.25
Number of eligible children to be enrolled18,00010,000
Observed non-accidental deaths/non-accidental hospitalizations rates15/1000 pyrs*48/1000 pyrs**
Harmonic mean of total projected accumulated observation time per cluster84 pyrs40 pyrs
Expected reduction30%25%
Power80%80%
  1. *Assuming that our observed composite outcome rate (15/1000 pyrs) is an average of the rates in our control and intervention clusters, and that the real difference between the clusters is 30%, we assumed the rates to be 17/1000 pyrs in control clusters and 12/1000 pyrs in intervention clusters when re-evaluating our power calculations
  2. **Assuming that our observed composite outcome rate (48/1000 pyrs) is an average of the rates in our control and intervention clusters, and that the real difference between the clusters is 25%, we assumed the rates to be 55/1000 pyrs in control clusters and 41/1000 pyrs in intervention clusters when re-evaluating our power calculations
  3. Abbreviation: Pyrs = person-years at risk