Interaction of history and intervention. If extraneous events occur concurrently during the intervention, they may not be present at other times, thus reducing the generalizability of the results of...

Interaction of history and intervention. If extraneous events occur concurrently during the intervention, they may not be present at other times, thus reducing the generalizability of the results of the original study. Example: The first community mental health center opened amid the shock of recent suicides of several young, unemployed men. It was forced to respond to the needs of persons facing socioeconomic pressures. However, when a new center opened in a nearby area, there was no similar popular recognition of this type of counseling, and considerably fewer persons went to the second center than to the first.