The term observer effect generally refers to the possibility that an act of observation may affect the properties of what is observed. However, depending on the context and the mechanisms involved, it may indicate effects of a very different nature. Observer effects are a threat to validity in much of educational research. After providing examples of observer effects to illustrate its meaning, this entry examines how to limit observer effect. The entry also considers common misconceptions about observer effect.

Sassoli de Bianchi, M. (2018). Observer Effect. In: The SAGE Encyclopedia of Educational Research, Measurement, and Evaluation. Edited by: Bruce B. Frey. SAGE Publications, Inc., pp. 1172-1174. Doi: 10.4135/9781506326139.n484.