ABSTRACT
The preceding chapters drew a clear distinction between research classified as experimental and research that is correlational: In correlational research, the investigator’s role is that of an observer. All variables of interest are permitted to vary freely in their natural context. In a real sense, all the variables in correlational studies are dependent variables. The researcher’s job in these research contexts is to assess this variation and to tease out the patterns and interrelationships that exist among the critical measures. On the other hand, in experiments, the researcher actively intervenes in the normal pattern of covariation, systematically controlling variation in the independent variable (or variables) to assess its causal impact. For purposes of internally valid cause-effect analysis, controlled manipulation of the causal variable and random assignment of subjects to the manipulated conditions are the necessary hallmarks of true experiments.
