title: Descriptive studies: what they can and cannot do.
abstract: Descriptive studies often represent the first scientific toe in the water in new areas of inquiry. A fundamental element of descriptive reporting is a clear, specific, and measurable definition of the disease or condition in question. Like newspapers, good descriptive reporting answers the five basic W questions: who, what, why, when, where. and a sixth: so what? Case reports, case-series reports, cross-sectional studies, and surveillance studies deal with individuals, whereas ecological correlational studies examine populations. The case report is the least-publishable unit in medical literature. Case-series reports aggregate individual cases in one publication. Clustering of unusual cases in a short period often heralds a new epidemic, as happened with AIDS. Cross-sectional (prevalence) studies describe the health of populations. Surveillance can be thought of as watchfulness over a community; feedback to those who need to know is an integral component of surveillance. Ecological correlational studies look for associations between exposures and outcomes in populations-eg, per capita cigarette sales and rates of coronary artery disease-rather than in individuals. Three important uses of descriptive studies include trend analysis, health-care planning, and hypothesis generation. A frequent error in reports of descriptive studies is overstepping the data: studies without a comparison group allow no inferences to be drawn about associations, causal or otherwise. Hypotheses about causation from descriptive studies are often tested in rigorous analytical studies.
authors.affiliation: Family Health International, PO Box 13950, Research Triangle Park, NC 27709, USA. dgrimes@fhi.org
authors.forename: David A
authors.initials: DA
authors.lastname: Grimes
authors.forename: Kenneth F
authors.initials: KF
authors.lastname: Schulz
mesh_terms: D015982:Bias; D016022:Case-Control Studies; D015984:Causality; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D003625:Data Collection / Q000379:methods / Q000592:standards; D003627:Data Interpretation, Statistical; D004781:Environmental Exposure / Q000009:adverse effects / Q000032:analysis; D015340:Epidemiologic Research Design; D006285:Health Planning; D006801:Humans; D008499:Medical Records; D019370:Observation; D011159:Population Surveillance; D015995:Prevalence; D011643:Publishing; D015203:Reproducibility of Results