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- A cross-sectional study (also known as a cross-sectional analysis, transverse study, prevalence study) is a type of observational study that analyzes data from a population, or a representative subset, at a specific point in time.
- It examines the relationship between diseases (or other health-related states) and other variables of interest as they exist in a defined population at a single point in time or over a short period of time (e.g. calendar year).
- Cross-sectional studies can be thought of as providing a snapshot of the frequency of a disease or other health-related characteristics (e.g. exposure variables) in a population at a given point in time.
- Cross-sectional studies measure the prevalence of disease and thus are often called prevalence studies.
- They are used to assess the burden of disease or health needs of a population and are particularly useful in informing the planning and allocation of health resources.
- In a cross-sectional study, the measurements of exposure and effect are made at the same time.
- The most common type of cross-sectional studies is the environmental health survey, in which participants are enrolled from exposed and unexposed areas to collect the information on health status, exposure to environmental factors, and potential confounding factors.
- As the disease and exposure data are collected simultaneously, the causal temporality of disease and exposure needs further evaluation.
In a cross-sectional study, all factors (exposure, outcome, and confounders) are measured simultaneously. The main outcome measure obtained from a cross-sectional study is prevalence, that is:
In an analytical cross-sectional study, the odds ratio can be used to assess the strength of an association between a risk factor and health outcome of interest, provided that the current exposure accurately reflects the past exposure.
Types of Cross-sectional Study
- A cross-sectional survey may be purely descriptive and used to assess the burden of a particular disease in a defined population.
- For example, a random sample of schools across London may be used to assess the prevalence of asthma among 12-14-year-olds.
- Analytical cross-sectional surveys may also be used to investigate the association between a putative risk factor and a health outcome.
- However, this type of study is limited in its ability to draw valid conclusions as to the association between a risk factor and health outcome. In a cross-sectional survey, the risk factors and the outcome are measured simultaneously, and therefore it may be difficult to determine whether the exposure proceeded or followed the disease.
In practice, cross-sectional studies will include an element of both types of design.
Applications of Cross-sectional studies
- Cross-sectional studies are relatively easy and inexpensive to conduct and are useful for investigating exposures that are fixed characteristics of individuals, such as ethnicity or blood group.
- In sudden outbreaks of disease, a cross-sectional study to measure several exposures can be the most convenient first step in investigating the cause.
- Data from cross-sectional studies are helpful in assessing the health care needs of populations.
- Data from repeated cross-sectional surveys using independent random samples with standardized definitions and survey methods provide useful indications of trends.
- Many countries conduct regular cross-sectional surveys on representative samples of their populations focusing on personal and demographic characteristics, illnesses and health-related habits.
- Frequency of disease and risk factors can then be examined in relation to age, sex, and ethnicity.
- Cross-sectional studies of risk factors for chronic diseases have been done in a wide range of countries.
Advantages of Cross-sectional studies
- Relatively quick and easy to conduct (no long periods of follow-up).
- Data on all variables is only collected once.
- Able to measure prevalence for all factors under investigation.
- Multiple outcomes and exposures can be studied.
- The prevalence of the disease or other health-related characteristics is important in public health for assessing the burden of disease in a specified population and in planning and allocating health resources.
- Good for descriptive analyses and for generating hypotheses.
Limitations of Cross-sectional studies
- Difficult to determine whether the outcome followed exposure in time or exposure resulted from the outcome.
- Not suitable for studying rare diseases or diseases with a short duration.
- As cross-sectional studies measure prevalent rather than incident cases, the data will always reflect determinants of survival as well as aetiology.
- Unable to measure incidence.
- Associations identified may be difficult to interpret.
- Susceptible to bias due to low response and misclassification due to recall bias.
- Non-response is a particular problem affecting cross-sectional studies and can result in bias of the measures of outcome. This is a particular problem when the characteristics of non-responders differ from responders.
- Park, K. (n.d.). Park’s textbook of preventive and social medicine.
- Gordis, L. (2014). Epidemiology (Fifth edition.). Philadelphia, PA: Elsevier Saunders.