The Descriptive Method: Because psychology is an observational science, it necessarily relies on the experimenter to observe, catalogue, quantify, and interpret variables suspected of a causative relationship. While observation is, therefore, essential to the study of psychology, it also presents a potential weakness in the results observed (Carlson 2006). For example, in the above experiment, the experimenter could, through a series of well designed experiments, determine that: (1) domestic violence perpetrators have, on average, a higher testosterone level than non-perpetrators; (2) other criminals do not, on average, have a higher testosterone level than non-criminals; and (3) none of the domestic violence perpetrators have a lower testosterone level than either non-perpetrators or non- criminals. Those results would seem to validate the initial hypothesis, that high testosterone levels are a causal factor in male perpetrators of domestic violence. However, the preceding series of experiments establishes only that there is a correlation between high testosterone levels and domestic violence; it does not necessarily justify any conclusion that the former causes the latter. In fact, it may be the exact reverse: perpetrating domestic violence may be the cause of high testosterone levels rather than the reverse. Actually, researchers have determined that aggression and testosterone are sometimes related in precisely that fashion: aggression does sometimes raise testosterone levels temporarily (Gerrig & Zimbardo...

Their purpose is to compare the variables considered in any experiment to identify errors in initial assumptions as well as among the variables themselves. In the case of the proposed connection between testosterone and domestic violence, correctional studies would suggest using the control groups of non-criminals and non-violent criminals. More importantly, correctional studies would also consider whether high testosterone and domestic violence are merely concurrent results of another variable rather than being causally related to each other. Perhaps early foundational experiences, such as witnessing domestic violence as a child, or being physically abused as a child) cause both high testosterone in adult males and increased incidence of domestic violence perpetration, in which case neither is a cause of the other.
Ultimately, psychological experimentation requires the combination of a disprovable hypothesis, a validly-designed experimental test, observation of results, identification of concurrent variables, the elimination of alternative explanations for apparent results, and the logical analysis of any conclusions based on the experiment.

REFERENCES Carlson, N.R. (2006) Physiology of Behavior 9th Edition. Boston: Allyn & Bacon. Gerrig, R, Zimbardo, P. (2005) Psychology and Life. 17th Edition.

New York: Allyn & Bacon.