Causal Studies’ Acausal Counterparts

Abstract

In community-level preventive medicine the core mission of reducing morbidity from various illnesses involves two principal components: reduction of the occurrence of causes of illnesses and reduction of people’s susceptibilities to such causes as remain.

When decisions about these actions – quitting smoking or undergoing vaccination, for example – are taken by individual members of the cared-for population – in response to community-level health education – people’s rational decisions about them require assessments of their personal risks for the illnesses that are at issue. Insofar as the knowledge-base for this is available – from population-level epidemiological research, acausal/descriptive – individuals in the cared-for population can perform their personal risk assessments on the basis of a web-based system arranged by the health educators.

The knowledge-base of these risk assessments is constituted by risk functions. For a given one of these, the domain is one in which the risk assessment is done, and subdomains within this are defined by risk/prognostic indicators for the health outcome at issue. The risk function, thus, expresses the cumulative probability of the health event’s occurrence over prospective/prognostic time as a function of that time (T) jointly with the prognostic indicators at the time of the risk assessment (at prognostic T₀). The risk function is predicated on no change in the risk factors (causal) over the time horizon addressed by the function.

In an acausal prognostic study, as in an intervention-prognostic study, a cohort is enrolled from the risk function’s domain of application, and the study base is formed by this cohort’s prospective course (away from the domain of application). A case series from this study base is coupled with an unstratified sample of this population-time, to be able to assess incidence-density function subject to translation into the corresponding function for cumulative incidence – and hence risk – from T₀ to T.