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 14-1, 14-5, 14-6, 14-9. and 14-10. 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.
Other sources of these problems include
Dunbar, G. (2005). Evaluating research methods in psychology: A case
study approach. Malden, MA:
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 9.
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