Table 1 Characteristics of Efficacy vs. Effectiveness Trial Designs (after [8])

Validity Priority

Internal > External

External ≥ Internal

Population and Sample

• Highly selected for condition of interest, narrowly defined

• Selected for condition of interest, reflecting presentation in source population

• Few comorbidities

• Comorbidities resemble those in population to which results will be applied; only those who cannot practically or ethically participate are excluded

• Willing and motivated participants

Intervention

• Intervention staff are highly qualified

• Staff selection, training, and fidelity monitoring resemble those likely to be feasible in target sites outside of the protocol proper

• Training may be intensive

• Fidelity monitoring may be similarly intensive

Outcome Measures and Data Collection

• Outcome measurements can be extensive, casting a wide net for potential secondary effects, moderators and mediators, or adverse effects

• Outcome batteries minimize respondent burden (in terms of both frequency and length of assessments) since subjects are heterogeneous in their willingness and capability to participate

• Since subjects are motivated, respondent burden less of a concern

• Accordingly, outcome measures chosen carefully to target fewer outcomes, and must be simple to complete

Data Analysis

• Standard statistical approaches suffice, and data-intensive analyses may be feasible

• Analyses to account for greater sample heterogeneity

• Analyses account for more missing data and data not missing at random