What is a cross-sectional study?

A cross-sectional study is a type of research design in which you collect data from many different individuals at a single point in time. In cross-sectional research, you observe variables without influencing them.

Researchers in economics, psychology, medicine, epidemiology, and the other social sciences all make use of cross-sectional studies in their work. For example, epidemiologists who are interested in the current prevalence of a disease in a certain subset of the population might use a cross-sectional design to gather and analyze the relevant data.

Cross-sectional vs longitudinal studies

The opposite of a cross-sectional study is a longitudinal study. While cross-sectional studies collect data from many subjects at a single point in time, longitudinal studies collect data repeatedly from the same subjects over time, often focusing on a smaller group of individuals that are connected by a common trait.

Cross-sectional vs longitudinal studies

Both types are useful for answering different kinds of research questions. A cross-sectional study is a cheap and easy way to gather initial data and identify correlations that can then be investigated further in a longitudinal study.

Cross-sectional vs longitudinal example
You want to study the impact that a low-carb diet has on diabetes. You first conduct a cross-sectional study with a sample of diabetes patients to see if there are differences in health outcomes like weight or blood sugar in those who follow a low-carb diet. You discover that the diet correlates with weight loss in younger patients, but not older ones.

You then decide to design a longitudinal study to further examine this link in younger patients. Without first conducting the cross-sectional study, you would not have known to focus on younger patients in particular.

When to use a cross-sectional design

When you want to examine the prevalence of some outcome at a certain moment in time, a cross-sectional study is the best choice.

Example
You want to know how many families with children in New York City are currently low-income so you can estimate how much money is required to fund a free lunch program in public schools. Because all you need to know is the current number of low-income families, a cross-sectional study should provide you with all the data you require.

Sometimes a cross-sectional study is the best choice for practical reasons – for instance, if you only have the time or money to collect cross-sectional data, or if the only data you can find to answer your research question was gathered at a single point in time.

As cross-sectional studies are cheaper and less time-consuming than many other types of study, they allow you to easily collect data that can be used as a basis for further research.

Descriptive vs analytical studies

Cross-sectional studies can be used for both analytical and descriptive purposes:

  • An analytical study tries to answer how or why a certain outcome might occur.
  • A descriptive study only summarizes said outcome using descriptive statistics.
Descriptive vs analytical example
You are studying child obesity. A descriptive study might look at the prevalence of obesity in children, while an analytical study might examine exercise and food habits in addition to obesity levels to explain why some children are much more likely to be obese than others.

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How to perform a cross-sectional study

To implement a cross-sectional study, you can rely on data assembled by another source or collect your own. Governments often make cross-sectional datasets freely available online.

Prominent examples include the censuses of several countries like the US or France, which survey a cross-sectional snapshot of the country’s residents on important measures. International organisations like the World Health Organization or the World Bank also provide access to cross-sectional datasets on their websites.

However, these datasets are often aggregated to a regional level, which may prevent the investigation of certain research questions. You will also be restricted to whichever variables the original researchers decided to study.

If you want to choose the variables in your study and analyze your data on an individual level, you can collect your own data using research methods such as surveys. It’s important to carefully design your questions and choose your sample.

Advantages and disadvantages of cross-sectional studies

Like any research design, cross-sectional studies have various benefits and drawbacks.

Advantages

  • Because you only collect data at a single point in time, cross-sectional studies are relatively cheap and less time-consuming than other types of research.
  • Cross-sectional studies allow you to collect data from a large pool of subjects and compare differences between groups.
  • Cross-sectional studies capture a specific moment in time. National censuses, for instance, provide a snapshot of conditions in that country at that time.

Disadvantages

  • It is difficult to establish cause-and-effect relationships using cross-sectional studies, since they only represent a one-time measurement of both the alleged cause and effect.
  • Since cross-sectional studies only study a single moment in time, they cannot be used to analyze behavior over a period of time or establish long-term trends.
  • The timing of the cross-sectional snapshot may be unrepresentative of behavior of the group as a whole. For instance, imagine you are looking at the impact of psychotherapy on an illness like depression. If the depressed individuals in your sample began therapy shortly before the data collection, then it might appear that therapy causes depression even if it is effective in the long term.

Frequently asked questions about cross-sectional studies

What is the difference between a longitudinal study and a cross-sectional study?

Longitudinal studies and cross-sectional studies are two different types of research design. In a cross-sectional study you collect data from a population at a specific point in time; in a longitudinal study you repeatedly collect data from the same sample over an extended period of time.

Longitudinal study Cross-sectional study
Repeated observations Observations at a single point in time
Observes the same group multiple times Observes different groups (a “cross-section”) in the population
Follows changes in participants over time Provides snapshot of society at a given point
Why do a cross-sectional study?

Cross-sectional studies are less expensive and time-consuming than many other types of study. They can provide useful insights into a population’s characteristics and identify correlations for further research.

Sometimes only cross-sectional data is available for analysis; other times your research question may only require a cross-sectional study to answer it.

What are the disadvantages of a cross-sectional study?

Cross-sectional studies cannot establish a cause-and-effect relationship or analyze behavior over a period of time. To investigate cause and effect, you need to do a longitudinal study or an experimental study.

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Lauren Thomas

Lauren has a bachelor's degree in Economics and Political Science and is currently finishing up a master's in Economics. She is always on the move, having lived in five cities in both the US and France, and is happy to have a job that will follow her wherever she goes.

2 comments

Taremwa Lawrence
October 16, 2020 at 8:11 AM

Very appreciative

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Jay
October 15, 2020 at 6:08 PM

I really liked this article because it helped me understand a lot concerning cross sectional studies

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