This is the tendency of people to act or appear differently when they know that they are being observed. It is also known as the Hawthorne Effect. Back in the 1920′s a study was conducted at a manufacturing facility called the Hawthorne Works. The goal was to see if different levels of light affected worker productivity. They soon found that changing the level of light caused productivity to soar. Unfortunately, when the study was over, productivity sank back down to normal levels. This is because the increase was not due to the level of light; it was due to the fact that the workers were being watched. Reactivity generally results in motivating people who are being observed to alter their behavior to make them look better. It can be a real problem in research studies.