Discuss internal validity
Students tend to accept that correlation implies causality. Even those who argue that only experiments establish causality, do not seem to realize that, even in experiments, causality is an inference rather than an incontrovertible fact. To stress that internal validity is difficult to establish, go over tables 13.3 and 13.7. Conclude by giving them some problems that ask them to determine whether a study has internal validity. Unfortunately, almost daily, one finds these flawed studies presented in the popular media. Another source of these problems is
Huck, S. W. & Sandler, H. W.(1986) Rival Hypotheses: Alternative Interpretations of Data Based Conclusions
. New York: Harper and Row.
Note: In discussing internal validity, you may want to use some of the exercises or activities described in Chapter 8.
Back to Chapter Menu