Descriptive studies: what they can and cannot do

Lancet. 2002 Jan 12;359(9301):145-9. doi: 10.1016/S0140-6736(02)07373-7.


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.

Publication types

  • Review

MeSH terms

  • Bias
  • Case-Control Studies
  • Causality
  • Cluster Analysis
  • Cross-Sectional Studies
  • Data Collection / methods
  • Data Collection / standards
  • Data Interpretation, Statistical
  • Environmental Exposure / adverse effects
  • Environmental Exposure / analysis
  • Epidemiologic Research Design*
  • Health Planning
  • Humans
  • Medical Records
  • Observation
  • Population Surveillance
  • Prevalence
  • Publishing
  • Reproducibility of Results