Elsevier

The Lancet

Volume 359, Issue 9301, 12 January 2002, Pages 145-149
The Lancet

Series
Descriptive studies: what they can and cannot do

https://doi.org/10.1016/S0140-6736(02)07373-7Get rights and content

Summary

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.

Section snippets

Five “W” questions

Traditional descriptive epidemiology has focused on three key features: person, place, and time,4 or agent, host, and environment.5 An alternative approach is that of newspaper coverage. Good descriptive research, like good newspaper reporting, should answer five basic “W” questions—who, what, why, when, and where—and an implicit sixth question, so what?

Who has the disease in question? Age and sex are universally described, but other characteristics might be important too, including race,

Types of descriptive studies

Descriptive studies consist of two major groups: those that deal with individuals and those that relate to populations. Studies that involve individuals are the case report, the case-series report, cross-sectional studies, and surveillance, whereas ecological correlational studies examine populations.4

Trend analysis

Descriptive studies have several useful roles. Being able to monitor the health of populations is important to health-care administrators. Trend analysis is often provided by ongoing surveillance. Examples include the emerging epidemic of syphilis in the Russian Federation,52, 53 and the international epidemic of multiple births, prematurity, and low birthweight caused by assisted reproductive technologies.54, 55, 56, 57, 58 Both epidemics raise troubling societal issues.

Planning

A second use is

Advantages and disadvantages

Descriptive studies have both strengths and weaknesses. Often, the data are already available and thus inexpensive and efficient to use. Furthermore, few ethical difficulties exist. However, descriptive studies have important limitations. Temporal associations between putative causes and effects might be unclear. A dangerous pitfall is that the investigators might draw causal inferences when none is possible.27

Conclusion

Descriptive studies are often the first, tentative approach to a new event or condition. These studies generally emphasise features of a new disease or assess the health status of communities. Health administrators use descriptive studies to monitor trends and plan for resources. By contrast, epidemiologists and clinicians generally use descriptive reports to search for clues of cause of disease—ie, generation of hypotheses. In this role, descriptive studies are often a springboard into more

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