Evaluating the Experiment: Internal Validity
So far we have focused on the notion of validity in connection with operating procedures. We want to develop procedures that define our variables in valid ways However, a more general evaluation is also require: Is the experiment valid? Have we made valid measurement of the effects of the independent variable? (Box 6-2 presents an important measurements validity issue to consider) We can talk about two kind of validity when we look at the experiment as a whole. The first is internal validity – the degree to which a researcher is able to state a causal relationship between antecedent conditions and the subsequent observed behavior. Later in the book we will discuss external validity, how well the finding of the experiment generalize or apply t situations that were not tested directly (for example, real life). But before we can think about the external validity of an experiment, we must first evaluate its internal validity