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)
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 |