- A simple description of the health status of a community, based on routinely available data or on data obtained in special surveys, is often the first step in an epidemiological investigation. Such a study is termed as a descriptive study.
- A descriptive study – as the name implies – describes the distributions of disease, injury or health in a population, outlining the burden of disease or the extent of exposure.
- Pure descriptive studies make no attempt to analyze the links between exposure and effect.
- They summarize patterns of disease or of disease determinants in terms of time, place and person.
- They are usually based on mortality statistics and may examine patterns of death by age, sex, race or ethnicity during specified time periods or in various countries.
- They describe a health outcome by different characteristics of a person (race, age, or sex, for example), place (geographic location), and time (a specific year or a span of time). For example, the case fatality of cholera in 1854 in London was 40% (John Snow, the cholera outbreak in London).
- The results are used to understand a population’s health status, generate hypotheses about the causes of diseases, and inform program planning and evaluation. In other words, descriptive epidemiology describes the distribution of disease.
Types of Descriptive Studies
The types of descriptive studies include:
- Case reports or case series
- Correlational or ecologic studies
- Cross-sectional studies
- Prevalence surveys
Descriptive studies that examine individuals can take the form of case reports (a report of a single case of an unusual disease or association), case series (a description of several similar cases) and cross-sectional studies. Descriptive studies that examine populations, or groups, as the unit of observation, are known as ecological studies.
Applications of Descriptive Studies
- Descriptive epidemiology identifies non-random variation in the distribution of disease, injury or health.
- Their function is to describe the “who, what, why, when, where” without regard to the hypothesis, highlighting patterns of disease and associated factors.
- This allows the public health practitioner to generate testable hypotheses regarding why such variation occurs.
- Descriptive epidemiology identifies who is affected, when, and where the situation is occurring in the community or population of interest. This is an important tool for health services planning and programming.
- Pure descriptive studies are rare, but descriptive data in reports of health statistics are a useful source of ideas for epidemiological studies.
- Limited descriptive information (such as that provided in a case series) in which the characteristics of several patients with a specific disease are described but are not compared with those of a reference population, often stimulates the initiation of a more detailed epidemiological study.
For example, the description in 1981 of four young men with a previously rare form of pneumonia was the first in a wide range of epidemiological studies on the condition that became known as the acquired immunodeficiency syndrome (AIDS).
Advantages of Descriptive Studies
- Descriptive (including ecological) studies are generally relatively quick, easy and cheap to conduct.
- Exposure data often only available at the area level.
- Differences in exposure between areas may be bigger than at the individual level, and so are more easily examined.
- Utilization of geographical information systems to examine the spatial framework of disease and exposure.
- A descriptive study is limited to a description of the occurrence of a disease in a population.
- It is unable to test hypotheses.
- Weaknesses of case reports and case series are that they have no comparison (control) group, they cannot be tested for statistical associations, and they are especially prone to publication bias (especially where case reports/series describe the effectiveness of an intervention).
- Park, K. (n.d.). Park’s textbook of preventive and social medicine.
- Gordis, L. (2014). Epidemiology (Fifth edition.). Philadelphia, PA: Elsevier Saunders.