Reactivity, also known as the observer effect, takes place when the act of doing the research changes the behavior of participants, thereby making the findings of the research subject to error.

Different types of reactivity have been identified. One of the first to be noted, the Hawthorne effect, is associated with experiments conducted by Elton Mayo at the Westinghouse Electric plant in Hawthorne, Illinois, during the 1920s and 1930s. Modifications in working conditions (e.g., changes in lighting) were introduced, and it was observed that productivity increased after each modification. Mayo hypothesized that workers were responding to increased attention received as being part of the experiment and knowing they were being observed rather than to the changes in work process. The Hawthorne effect encompasses changes in behavior arising from knowledge about participation in research. Another type of reactivity is the novelty effect, which involves changes in behavior due to the introduction of something new in the research setting (e.g., the presence of the researcher). Novelty effects usually disappear with passing time. The placebo effect has been well documented in drug trial research but also can occur in other research settings. Finally, reactivity may result from demand characteristics, with participants doing what they think the researcher expects them to do or what will please the researcher.

A number of factors have been seen to influence the degree of reactivity. Conspicuous observers, or those who place themselves in the middle of the activities, are more intrusive than those who stand to the side. Characteristics of the observer (e.g., age, race, gender, dress) that differ substantially from those of participants are likely to cause more reactivity. Characteristics of participants may also influence behavior. For example, children usually return to naturally occurring behavior more quickly than do adults. Reactive behavior usually decreases as time passes, a process known as habituation. It is postulated that this return to normality arises from the development of rapport and trust between participants and the researcher and the fact that it is difficult to sustain unnatural behavior for a long period. Participants' understanding of the purpose of the research may cause reactivity. For example, if participants believe that the researcher is trying to document socially unacceptable or deviant activities, they may hide these behaviors.

In qualitative research, reactivity is usually seen as being inclusive of the researcher as well as the participants. The researcher keeps reflexive notes that document how his or her own behavior and understandings may have been affected by the research process. Reactivity is regarded as being inevitable in any research process that involves interaction among participants, the researcher, and a setting of interest. Reflexive analysis helps to uncover and respond to reactivity in appropriate ways.

Lynne E. F. McKechnie

Further Readings

Palys, T.(2003).Threats to validity: Dealing with reactivity. In T.Palys (Ed.), Research decisions: Quantitative and qualitative perspectives (
3rd ed.
, pp. 207–208).Scarborough: Thomson Nelson Canada.
Paterson, B. L. A framework to identify reactivity in qualitative research. Western Journal of Nursing Research (1994)., 16. 301–316.
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