When conducting studies, researchers need to be careful of the Hawthorne effect, or the possibility that their active participation with study participants can influence the data.
This means that the researcher or experimenter's presence in a research study might influence the way in participants answer questions or perform in a research study. This in turn, compromises the validity of research findings. When a participant is influenced by the researcher's presence in a study, it might lead to a phenomenon where the participant answers questions or performs in a way he or she thinks the experimenter expects.