A cross-sectional study is the simplest variety of descriptive or observational epidemiology that can be conducted on representative samples of a population. Simply put, it is a study that aims to describe the relationship between diseases (or other health-related states) and other factors of interest as they exist in a specified population at a particular time, without regard for what may have preceded or precipitated the health status found at the time of the study. For instance, a single cross-sectional study may include questions about smoking behavior, occupational exposure to dusts and fumes, respiratory symptoms (cough, breathlessness), and physical examinations of physical fitness—including simple tests of lung function. Such a study would throw some light on the relationship of both occupational exposures and smoking behavior to respiratory symptoms and respiratory function. However, it is impossible either to establish causal relationships or to get reliable perspectives on the natural history of respiratory disease from such a study.
Cross-sectional studies must be done on representative samples of the population if generalizations from the findings are to have any validity. These studies gather information about the prevalence of health-related states and conditions, but they cannot distinguish between newly occurring and long-established conditions. All they can do is measure the frequency (prevalence) of conditions and demonstrate associations. They cannot identify cause-and-effect relationships, though they do identify the existence of health problems.
Cross-sectional studies, also known as surveys, are a useful way to gather information on important health-related aspects of people's knowledge, attitudes, and practices (such studies are known as "KAP" surveys). In the area of reproductive health, such a survey might include questions such as:
The U.S. National Health Surveys are a form of cross-sectional study. Like many other cross-sectional studies, they can identify health problems and provide data from which many useful inferences can be made and hypotheses generated.
Cross-sectional studies are often used as a basis for health-policy decisions, and it is important to ensure that only current, rather than obsolete, information is used for this purpose. When health department resources are limited, information gathered in a cross-sectional study in the past can usually be refreshed with up-to-date facts from a small sub-sample; it would be necessary to repeat a large cross-sectional study only if the findings from a current sub-sample are seriously discrepant from earlier results.
JOHN M. LAST
Abramson, J. H., and Abramson, Z. H. (2000). Survey Methods in Community Medicine, 5th edition. Edinburgh & London: Livingstone.
Kelsey, J. E.; Whittemore, A. S.; Evans, A. S.; and Thompson, D. (1996). Methods in Observational Epidemiology, 2nd edition. New York: Oxford University Press.