Cluster randomized trials: opportunities and barriers identified by leaders of eight health plans.
Mazor KM, Sabin JE, Boudreau D, Goodman MJ, Gurwitz JH, Herrinton LJ, Raebel MA, Roblin D, Smith DH, Meterko V, Platt R. Cluster randomized trials: opportunities and barriers identified by leaders of eight health plans. Med Care. 2007 Oct; 45(10 Supl 2):S29-37.