Research In Brief: Prevalence Studies

NARIC’s Research In Focus series highlights new and interesting findings from NIDILRR-funded studies, presented in lay language summaries. The series covers a wide array of topics and aims to present peer-reviewed research in readable formats, so our readers can learn about issues that affect them every day. The Research in Brief companion series breaks down some of the concepts readers might come across when exploring research in disability and rehabilitation. This issue introduces the concepts of prevalence, incidence, and prevalence studies.

Imagine for a moment you see a photograph of a smiling family standing in front of a hospital. What information can you glean from looking at this image? You can see the people, the hospital in the background, perhaps even what the weather was like on that day. But you don’t know much about who the people are or why they’re standing in front of the hospital. Prevalence studies, also known as, cross-sectional studies are sometimes described as taking a snapshot of the health of a population. Just in the way a photograph captures a moment in time, prevalence studies can capture the state of disability or disease in a group of people at a given time.

What is prevalence?

In research, prevalence is a measure of the overall number of people with a disease in a given population. For example, roughly 37.3 million (11.3%) people in the US have type 2 diabetes. Another way to say this is that the prevalence of diabetes in the US is 11.3%. Sometimes prevalence is mentioned along with another measure called incidence. Incidence is the number of new cases of a disease in a given period of time. In 2019, 1.4 million people were newly diagnosed with diabetes; this would be the incidence rate of diabetes in the US. Prevalence studies are a great way to determine what the overall burden of a disease or a condition is among a population. Prevalence studies can also look at conditions within specific populations. For example, studies have shown that diabetes prevalence rates are higher among people with cognitive disabilities than those without cognitive disabilities.

How do prevalence studies work?

Let’s say for example, researchers wanted to know how common visual disabilities or eye conditions are among people with diabetes. This could be helpful information for both clinicians and patients with diabetes. A prevalence study could be as simple as randomly selecting a group of people with diabetes and asking them if they have been diagnosed with low vision or any eye conditions such as glaucoma or cataracts. The answer to this question could then form the basis for whether early interventions such as yearly eye screenings were needed for this specific group of people.

What are some benefits to prevalence studies?

Prevalence studies are generally simpler than other study designs and therefore less expensive and time consuming. In prevalence studies, the questions are usually easy to answer and do not require participants to return for follow-up questions. They can also use existing data such as medical records or databases like the National Spinal Cord Injury Database. That does not mean that prevalence studies are less important than cohort or case-control studies. Prevalence studies can help researchers determine whether or not a particular health problem is affecting a given population and how much of an impact a disease may have on a population. Looking back at our example, prevalence studies have shown that nearly 1 in 10 Americans have diabetes raising the alarm that diabetes is a top public health concern. Prevalence studies can also help us identify opportunities for education and health promotion, such as the study on diabetes and cognitive disabilities. Based on those findings, researchers may develop a diabetes education program targeted to that community’s needs.

What are some limitations of prevalence studies?

Prevalence studies are only giving us a picture of the health of a population in a particular moment or period of time. They cannot give us any more information about the long-term effects or even the cause of what we’re seeing. For example, there are a number of questions the prevalence of eye diseases in people with diabetes does not let us know. How many people were newly diagnosed with an eye disease in a given year (incidence)? Did the vision problems start a year after their diabetes diagnosis or ten years in? Among the people who said they didn’t have eye disease, how many of them would go on to develop vision problems in the future? Why were some people with diabetes developing eye disease versus others? What factors were causing the prevalence of eye disease among people with diabetes? Researchers would need to conduct long-term studies to know the answer to these questions.

Prevalence studies help researchers and clinicians accurately predict the presence of disease in a population in a relatively quick and efficient manner. Oftentimes, prevalence studies are used as a starting point for more research. They provide information for researchers to tailor their future study designs. When we know how many people have a health issue, we can use interventions and resources where they’re needed the most.

Our Research In Focus series has highlighted many NIDILRR-funded studies which examine the prevalence of certain conditions within communities of people with disabilities. Here’s a small sample:

You can explore much more Research In Focus on our website!

Hafsa Abdirahman MPH is a public health scientist and freelance medical writer and editor. She believes that access to evidence-based, quality health information can save lives and she’s worked throughout her career to put this belief into practice.