Assessment Effects in Educational and Psychosocial Intervention Trials: An Important but Often-Overlooked Problem

Baseline assessments and repeated measures are an essential part of educational and psychosocial intervention trials, but merely measuring an outcome of interest can modify that outcome, either by the measurement process alone or by interacting with the intervention to strengthen or weaken the intervention effects. Assessment effects can result in biased estimates of intervention effects and may not be controlled by the usual two‐group randomized controlled trial design. In this paper, we review the concept of assessment effects and other related phenomena, briefly describe study designs that estimate assessment effects separately from intervention effects and discuss their strengths and limitations, review evidence regarding the strength of assessment effects in intervention trials targeting behavior change, and discuss implications for intervention research. © 2015 Wiley Periodicals, Inc.