Cochran’s Q statistic is computed from replicated measurements data with binary responses. This statistic tests a difference in effects among 2 or more treatments applied to the same set of experimental units.
Consider the results of a study of M treatments applied to N experimental units (e.g patients or laboratory animals). The outcomes of individual measurements for the (i)th treatment of the (j)th unit are binary variables {Vij; i=1,…,M; j=1,…,N} taking on two values “0” or “1” (e.g. “No effect” or “Effect is found”).
The Cochran Q statistic is computed by the formula
| M(M–1) | M Ã¥ i=1 | (Gi – mean(G) )2 |
| M | N ? j=1 | Lj – | N |