Mental Health: A Report by the Surgeon General

Quality research rests on accepted methods of testing hypotheses. Two of the more common research methods used in the mental health field are experimental research and correlational research. Experimental research is the preferred method for assessing causation but may be too difficult or too expensive to conduct. Experimental research strives to discover cause and effect relationships, such as whether a new drug is effective for treating a mental disorder. In an experimental study, the investigator deliberately introduces an intervention to determine its consequences (i.e., the drug’s efficacy). The investigator sets up an experiment comparing the effects of giving the new drug to one group of people, the experimental group, while giving a placebo (an inert pill) to another group, the so-called control group. The incorporation of a control group rules out the possibility that something other than the experimental treatment (i.e., the new drug) produces the results. The difference in outcome between the experimental and control group—which, in this case, may be the reduction or elimination of the symptoms of the disorder—then can be causally attributed to the drug. Similarly, in an experimental study of a psychological treatment, the experimental group is given a new type of psychotherapy, while the control or comparison group receives either no psychotherapy or a different form of psychotherapy. With both pharmacological and psychological studies, the best way to assign study participants, called subjects, either to the treatment or the control (or comparison) group is by assigning them randomly to different treatment groups. Randomization reduces bias in the results. An experimental study in humans with randomization is called a randomized controlled trial.

Correlational research is employed when experimental research is logistically, ethically, or financially impossible. Instead of deliberately introducing an intervention, researchers observe relationships to uncover whether two factors are associated, or correlated. Studying the relationship between stress and depression is illustrative. It would be unthinkable to introduce seriously stressful events to see if they cause depression. A correlational study in this case would compare a group of people already experiencing high levels of stress with another group experiencing low levels of stress to determine whether the high-stress group is more likely to develop depression. If this happens, then the results would indicate that high levels of stress are associated with depression. The limitation of this type of study is that it only can be used to establish associations, not cause and effect relationships. (The positive relationship between stress and depression is discussed most thoroughly in Chapter 4.)

Controlled studies—that is, studies with control or comparison groups—are considered superior to uncontrolled studies. But not every question in mental health can be studied with a control or comparison group. Findings from an uncontrolled study may be better than no information at all. An uncontrolled study also may be beneficial in generating hypotheses or in testing the feasibility of an intervention. The results presumably would lead to a controlled study. In short, uncontrolled studies offer a good starting point but are never conclusive by themselves.

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