ABSTRACT
This chapter investigates issues of experimental validity and links this with the different threats to validity relevant to experiments, in particular, and to all research methods in general. It reviews all the likely sources of error in experiments that might cause us to conclude, wrongly, that the authors have demonstrated an effect when none exists or to conclude that an effect doesn't exist when, in fact, it does. The chapter considers several factors that can lead to misinterpretation of the results of a study and link these to issues in the design of experiments and other research designs. If manipulation of the independent variable did not cause the dependent variable to change, then the experiment lacks internal validity. The authors have weak construct validity when, as in the imagery example just presented, our intended independent variable is not the actual causal variable in an experiment.
