Table 1.

Purpose, Intent, and Elements of Traditional Efficacy Studies and Practical Effectiveness Trials

IssueTraditional Efficacy StudyPractical Effectiveness Trial
I. Purpose and intent
    Study goalIsolate treatment mechanism; unique approachReplicable treatment
    Key criteriaInternal validityExternal validity
    Purpose/world viewIsolate causeUnderstand program in context
    Decisions regardingTheoryPractice and policy
II. Study elements
    ParticipantsHomogeneous, motivatedHeterogeneous, representative
    SettingsHomogeneous, single or few under control of investigatorHeterogeneous, multiple to evaluate generalization across settings
    InterventionIntensive, highly structured, complexLess intensive, moderate structure, and flexible to permit options
    Intervention staffResearch staff or highly trained expertsRegular staff in representative settings