Hawthorne effect is a generally accepted psychological theory that the behavior of an individual or a group will change to meet the expectations of the observer if they are aware their behavior is being observed.
In designing consumer research, this factor must be taken into consideration, by disguising or concealing the purpose or sponsor of the research.
For example, If XYZ Company conducts a taste test and tells the subjects that XYZ Company produced beverage No. 1, most respondents will say they prefer beverage No. 1. Thus, it is not a true test.
Similarly, if a test panel are told they are testing an appetite suppressant, they will begin to eat less.
This behavior was documented by a research team led by Elton Mayo in the 1920s at the Western Electric Company Hawthorne plant. In studying the effect of lighting on productivity, the researchers found that, regardless of the lighting conditions introduced, productivity improved.