Читать книгу Abnormal Psychology - William J. Ray - Страница 121

Logical procedures are also important for helping us understand the accuracy or validity of our ideas and research. Valid means true and capable of being supported. In studying mental illness, one important way to show that our ideas can be supported is to replicate them with different individuals in different locations. If we hypothesized that a certain type of stress led to depression, for example, then we would need to show that this is the case not only in our research clinic, but also in other clinics.

Historically, we have discussed various types of validity in psychology, which arise from differing contexts. These contexts range from developing types of tests to running experiments. The overall question is this: Does a certain procedure, whether it is a test of mental illness or an experiment, do what it was intended to do? There are two general types of validity (Campbell & Stanley, 1963).

internal validity: the ability to make valid inferences between the independent variables (IVs) and dependent variables (DVs)

external validity: also known as generalizability, the ability to apply the results from an internally valid experiment to other situations and other research participants

generalizability: also known as external validity, the ability to apply the results from an internally valid experiment to other situations and other research participants

The first is internal validity. The word internal refers to the experiment itself. Internal validity asks the following question: Is there another reason that might explain the outcome of our experimental procedures? Students are particularly sensitive to questions of internal validity, for example, when it is time for final exams; they can make a number of alternative suggestions about what the exam actually measures and why it does not measure their knowledge of a particular subject. Like students, scientists look for reasons (threats to internal validity) that a particular piece of research may not measure what it claims to measure. In the case of our friend from Boston, the absence of tigers near his house could have reflected a long-standing absence of tigers in his part of the world rather than the effectiveness of his yelling.

The second type of validity is external validity. The word external refers to the world outside the setting in which the experiment was performed. External validity often is called generalizability. Remember the story of Semmelweis. His finding that the deaths of the mothers who had just given birth were the result of physicians touching them after handling diseased tissue was true not only for his hospital, but also for all other hospitals. Thus, in addressing the question of external validity of Semmelweis’s work, we would infer that his answers could be generalized to other hospitals with other women and not just to his own original setting. External validity, therefore, refers to the possibility of applying the results from an internally valid experiment to other situations and other research participants.

We logically design our research to rule out as many alternative interpretations of our findings as possible and to have any new facts be applicable to as wide a variety of other situations as possible. In many real-life situations in which external validity is high, however, it is impossible to rule out alternative interpretations of our findings. In a similar way, in laboratory settings in which internal validity is high, the setting is often artificial, and in many cases our findings cannot be generalized beyond the laboratory. Consequently, designing and conducting research is always a trade-off between internal and external validity. Which one we emphasize depends on the particular research questions being asked.

Before continuing, let’s clear up one misconception. It is the idea of designing “the one perfect study.” Although we strive to design good research, there are always alternative explanations and conditions not included in any single study. It is for this reason that Donald Campbell, who introduced scientists to the idea of internal and external validity, also emphasized the importance of replicating studies. If the same study is performed a number of times with similar results, then we can have more assurance that the results were valid. Even better, if the study is performed in a variety of settings around the world, we have even more confidence in our results. I will return to this topic of replication later in the chapter.