Experimenter Effects

As social and behavioral scientists, it is of fundamental importance to understand the factors that drive the behaviors that we measure. Careful design is thus required to minimize the influence of extraneous factors. Yet, we often overlook one major class of such extraneous factors – those related to us, the experimenters. Experimenter effects can potentially arise at every step in the research process – from the selection of hypotheses, to interacting with research participants in ways that might alter their behavior, to biases in data interpretation. While such experimenter-driven effects often occur without notice, and without ill intent, they nonetheless threaten the replicability and generalizability of research. In this chapter, we discuss when and how such effects arise, preventative measures that can be taken to reduce their influence, and methods for accounting for such effects, when appropriate.