Main Effects & Interactions

Main effects represent the influence of a single variable, regardless of the levels of any other
independent variables in the study. A main effect indicates that a single independent variable has had a
significant impact on the dependent variable. Interactions, on the other hand, indicate that the influence of
one independent variable depends on the levels of one or more other independent variables.
Consider, for example, the causes of heart disease. If you ask me whether hypertension is a risk factor
for coronary disease, I can say “yes” without need for qualification. Hypertension is a main effect variable
for coronary heart disease. Regardless of other risk factors you may or may not have, the higher your blood
pressure, the greater your risk for developing coronary heart disease. On the other hand, if you ask if Type
A behavior is a risk factor for heart disease, I have to say that “it depends.” It depends, for example, on
whether you have a family history of heart disease and it depends on whether you experience a lot of dayto-day stress. Only when stress is high and you have a family predisposition for heart disease does Type A
confer any additional risk. Type A behavior is an interaction variable with regard to coronary heart disease.
Main effects and interactions can occur alone or together in the same data set. Moreover, they produce
distinct patterns of data that can be recognized in visual displays. This assignment is designed to give you
practice recognizing main effects and interactions. i PROVIDE A PAPER AND ASSIGNMENT PLEASE DO THE LAST PART