Clinical Trials and Intervention Studies

In a controlled observational cohort study, two groups of subjects are selected from two populations that (hopefully) differ in only one characteristic at the start. The groups of subjects are studied for a specific period and contrasted at the end of the study period. For instance, smokers and nonsmokers are studied for a period of 10 years, and at the end the proportions of smokers and nonsmokers that died in that period are compared. On the other hand, in an intervention study, the subjects are selected from one population with a particular characteristic present; then, immediately after baseline, the total study group is split up into a group that receives the intervention and a group that does not receive that intervention (control group). The comparison of the outcomes of the two groups at the end of the study period is an evaluation of the intervention. For instance, smokers can be divided into those who will be subject to a smoking-cessation program and those who will not be motivated to stop smoking. Interventions have the intention to improve the condition of an individual or a group of individuals. Some examples of intervention studies in public health research are studies that evaluate the impact of a program: (a) to promote a healthier lifestyle (avoiding smoking, reducing alcohol drinking, increasing physical activity, etc.), (b) to prevent HIV-transmission, (c) to start brushing teeth early in babies, and so on. Ample intervention studies can also be found in other disciplines; two examples illustrate this. First, Palmer, Brown, and Barrera [4] report on an intervention study that tests a short-term group program for abusive husbands against a control program. The two groups are compared with respect to the recidivism rates of the men regarding abuse of their female partners. Second, Moens et al. [1] evaluated in a controlled intervention study the effect of teaching of how to lift and transfer patients to nursing students in a nursing school. After two years of