Healthcare and Medicine Reference
Disease and exposure frequencies as well as studies of beneficial effects
of care (outcomes) such as improvement or cure are obtained either from
cohort studies (follow ups of disease occurrence in time in exposed and
unexposed groups) or case-control studies in which the exposure is com-
pared in cases and noncases of the health event of interest.
Here is an oversimplified example of noxious factors and following cases of
disease events studied both by cohort and case control studies. This example
should help us understand how disease cases, death, or favorable or unfavor-
able outcomes and exposures to various beneficial or noxious factors frequen-
cies and their comparisons are applied to various uses and interpretations.
Cohort (longitudinal) study
Case control (transversal) study
Frequencies of disease, death, or change in health status are numer-
ous. Morbidity (disease prevalence and incidence), mortality, case fatality,
and their relationships in the form of rates, ratios, or odds are the most
important ones. Figure 2.14 represents a simplified example of some such
100 develop pneumonia
50 die of it
(all exposed; i.e., individuals
at risk of having health problems)
400 will remain healthy
Figure 2.14 Morbidity, mortality, and case fatality in a health event. Periods of
exposure and event occurrence are defined.