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Table 2 Situations in which the matched-pair design is (or might be) better and those in which the stratified design is (or might be) better (shading indicates the situations prevailing in our study)

From: Cluster randomized trial of an active, multifaceted information dissemination intervention based on The WHO Reproductive health library to change obstetric practices: methods and design issues [ISRCTN14055385]

Matched pairs better Stratified better
Large variation between pairs with respect to baseline risk Within-stratum variation small compared to between-stratum variation
High matching correlation Small matching correlation within strata
No individual level analysis desired Analysis at individual level desired (2) (interactions of interventions with age, gender, medical history)
Homogeneity of effect can be assumed across pairs Heterogeneity of effect across strata possible
No drop-outs expected Individual hospitals may drop out
Medium number of clusters (20 to 40, so as to have 10–20 well-matched pairs) Large number of clusters (perhaps >30 or >40 depending on the number of strata)
Calculation of ICC(1) needs special assumptions Calculation of ICC straightforward
  1. (1) ICC – intracluster correlation coefficient (2) Only as secondary analysis in our study