Читать книгу Methods in Psychological Research - Annabel Ness Evans - Страница 75

You will recall that an independent variable (IV) is the variable in an experiment that is manipulated by the researcher. The researcher chooses levels of the IV that he or she thinks will have effects on some response measure. The researcher then assigns participants to each level of the IV (or all levels, in the case of repeated-measures designs) and compares the differences in response measures to see if the IV had an effect. You will recall that some variables are not true IVs. The values of these participant variables may be inherent in the participants. Examples include gender, age, disability type, and so on. Or participants might have self-selected the value of the variable. For example, differences in school success between children attending private and public schools is a comparison on a participant variable where the participants have, in effect, assigned themselves to the values of the variable. In either case, studies of group differences on participant variables are not true experiments; rather, they are quasi-experiments. Remember that a true IV is under the direct control of the researcher. The researcher chooses the values of the variable and assigns participants to each and then looks to see if that manipulation has any effect on the participants’ responses, the dependent variable. In an experiment, the IV can be thought of as the cause in a cause–effect relationship.

FYI

Statistical packages such as IBM® SPSS® Statistics do not distinguish between true IVs and participant (or subject) variables. They refer to both as IVs.