ABSTRACT
Trials are experimental studies on the effectiveness of interventions designed to treat or prevent disease. Sometimes a trial is called an intervention study because it is designed to test a hypothesized cause-effect relationship by modifying a causal factor in a group or population. A trial can be classified according to the level of prevention within which it operates. If primary prevention is the focus, then the study is considered a prophylactic trial, which targets subjects at low health risk. An interventive trial, by contrast, operates at the secondary level of prevention and targets subjects who are at high health risk. If treatment is the focus, a therapeutic trial is conducted since it operates at the tertiary level of prevention and targets persons who are cases of the disease (see Figure 12.1).
