Russel-Research-Method-in-Anthropology

Research Design: Experiments and Experimental Thinking 145
the amount of pain they had and a direct measure of the amount of pain medication
they took. All the patients had access to a device that let them administer
more or less of the analgesics that are used for controlling pain after orthopedic
surgery.
In assessing the results of a factorial experiment, researchers look for main
effects and interaction effects. Main effects are the effects of each independent
variable on each dependent variable. Interaction effects are effects on
dependent variables that occur as a result of interaction between two or more
independent variables. In this case, Rotton and Shats wanted to know the
effects of humor on postoperative pain, but they wanted to know the effect in
different contexts: in the context of choosing the vehicle of humor or not; in
the context of being led to believe that humor has healing benefits or not; and
so on.
As it turned out, being able to choose their own movie had no effect when
patients saw action films. But patients who saw humorous films and who had
not been able to make their own choice of film gave themselves more pain
killer than did patients who saw humorous films and had been able to make
the selection themselves (Rotton and Shats 1996).
We’ll look at how to measure these effects when we take up ANOVA, or
analysis of variance, in chapter 20.