Last update:
06-Jun-2005

Prognostic intervention studies can be either preventive intervention studies or therapeutic intervention studies. The formulation of prognosis about the progress of the health of an individual is one of the most important activities in health sciences. Prognosis is studied through epidemiological methodology. Prognostic studies can be either descriptive or intervention studies. The design of these studies comprises the design of the object and the method or content. The object is a prognostic occurrence function, that is, the frequency (incidence or prevalence) of the outcome occurrence in relation (descriptive or causal) to a determinant or a group of determinants in a specific domain. The method is the way by which the object is accomplished. Therapeutic intervention prognostic studies are widely known as clinical trials. The object of these studies corresponds to the incidence proportion or prevalence of the outcome under study in relation to the intervention under study at time T>T₀, where T₀ is the time of randomization, that is, the random allocation of the study subjects to the comparison groups. The two basic elements which need to be considered while designing the object are the nature and the domain of the causal prognostic occurrence function. The first, the nature, includes the design of (a) the outcome, which can be either a period event or a prospective state, as well as the scale upon which the frequency of the outcome will be measured, (b) the measure of the outcome frequency, that is the incidence proportion or prevalence in prognostic intervention studies, (c) the causal determinant(s) (potential or known) of the outcome frequency, which in this context correspond to the therapeutic interventions under study, (d) the time relation between the causal determinant status (the application of the intervention) and the outcome, (e) the modifiers, and (f) the known and unknown confounders of the causal relationship. The domain of the prognostic occurrence function is a series of person-moments, persons with a particular disease.

Key words: Clinical trials, Intervention studies, Study object.