Efficacy and effectiveness trials: examples from smoking cessation and bullying prevention.

If health psychology is to maximize impacts on health, there will need to be a shift from relying primarily on efficacy trials to increasing reliance on effectiveness trials. Efficacy trials use homogeneous, highly motivated samples with minimal complications from a single setting receiving intensive treatments delivered under highly controlled conditions. Two effectiveness trials on bullying prevention illustrate the use of a heterogeneous population from multiple sites receiving a low intensity tailored treatment delivered under highly variable conditions. In spite of considerable noise the effectiveness trials produced robust results (odds ratios of about four) that bode well for population impacts under real-world dissemination.