The overarching aim of reviews of prevalence and incidence data is to report on the frequency, distribution and determinants of specific factors, health states or conditions in a defined population.
Reviews that aim to describe the distribution of existing variables or seek to answer the question: how common is a particular disease or condition in a specific group of individuals?’ are often classified as descriptive and will utilise measures of prevalence and incidence to answer such lines of enquiry.
The objective of these reviews is to describe the health issue (what), those affected by it (who) as well as the location (where) and the time period (when) in which it occurred.
Accordingly, the review question should outline the factor, disease, symptom or health condition of interest, the epidemiological indicator used to measure its frequency (prevalence, incidence), the population or groups at risk, as well as the context/location (e.g., limited to specific geographic areas) and time period (e.g., peaks at a particular season) where relevant.
For example: The objective of this review is to assess the prevalence and incidence of peri-natal depression among women in Australia.
Reviews focusing on how and why are predominantly analytic in nature. The objective of reviews of explanatory or analytic studies is to contribute to and improve our understanding of the causes of health-related events or outcomes by isolating the association between specific factors. This element is non-existent or lacking in studies that are purely descriptive. While studies that report prevalence and incidence only are broadly classified as descriptive and those that examine associations between exposures and outcomes are broadly classified as analytical a clear-cut distinction between analytical and descriptive study designs is not possible. Data generated from these studies can be measured and reported in different ways and the review question will indicate whether the review seeks to report data that is descriptive, analytical or a combination of both.