Understanding the CDC’s New Report: What Are Diabetes Incidence and Prevalence?

, food systems & health analyst | December 2, 2015, 4:34 pm EDT
Bookmark and Share

Earlier this week, the Centers for Disease Control and Prevention (CDC) released their latest report on diabetes in the United States. According to the report, new cases of diabetes declined by 20 percent between 2008 and 2014. However, the number of people diagnosed with diabetes in the United States is still at an all-time sugar high. Since the 1980s, diabetes rates have more than quadrupled and approximately 9.3 percent of the population has been diagnosed with diabetes. So how can one statistic be declining (new cases) and the other be rising?

The answer to that lies in the science of epidemiology, “the study of the distribution and determinants of health related states and events in populations and the application of this study to control health problems”. When the CDC reports “new cases” it’s talking about diabetes incidence; when they report the “number of people diagnosed with diabetes” they’re talking about diabetes prevalence. But what’s the difference between these two and how are they related?

In epidemiology, incidence and prevalence are the two basic measures of calculating disease frequency. Incidence is the number of new cases during a certain time frame and is measured using the following equation:

Data Source: CDC, National Center for Health Statistics,

Incidence=           Number of new diabetes cases            _

                      Average population at risk * time interval

 

 

 

Prevalence is partly based on incidence and is calculated based on the proportion of the population that has been diagnosed:

Prevalence = Nprevalenceumber of existing (and new) diabetes cases

                                        Average population at risk

 

 

The two equations above show that prevalence depends on incidence: an increase in incidence will increase prevalence (assuming there isn’t a high level of mortality due to the disease). However, a decrease in incidence may not necessarily lead to a decrease in prevalence. One of the easiest ways to think about the relationship between incidence and prevalence is illustrated by Ann Aschengrau and George Seage’s sink model:

Sink

Diabetes disease incidence is represented by the water inflow from the faucet (each drop represents a newly diagnosed diabetes case). Diabetes prevalence is represented by the water level in the sink (it includes new and existing diabetes cases).  So while the inflow of water from the faucet may slow down, that doesn’t necessarily mean that the water level in the sink will change.

We can and should celebrate about the decline of new diabetes cases over the past five years, but we still need to focus on addressing diabetes prevalence. As Ann Albright, director of the CDC’s Division of Diabetes Translation, said during her interview about the new report with NPR yesterday : “we still have a long, long way to go.”


Author’s note: While I was an undergraduate student at the University of North Carolina’s Gillings School of Global Public Health, I took Professor Victor Schoenbach’s course on “The Principles of Epidemiology for Public Health.” At that time, I did not appreciate the educational foundation that was being built for me, but in recent years I am forever grateful to use these foundations as a sounding board for my public health explorations.

Posted in: Food and Agriculture Tags: , , ,

Support from UCS members make work like this possible. Will you join us? Help UCS advance independent science for a healthy environment and a safer world.

Show Comments


Comment Policy

UCS welcomes comments that foster civil conversation and debate. To help maintain a healthy, respectful discussion, please focus comments on the issues, topics, and facts at hand, and refrain from personal attacks. Posts that are commercial, self-promotional, obscene, rude, or disruptive will be removed.

Please note that comments are open for two weeks following each blog post. UCS respects your privacy and will not display, lend, or sell your email address for any reason.

  • Free Consult

    Dear Lindsey Haynes-Maslow,, thank you for your excellent article you put the title ” Understanding the CDC’s New Report: What Are Diabetes Incidence and Prevalence?”.By the way, I am very impressed by your excellent farm photography specially the hen photography. Keep it up. Waiting for your presence on How to Prune a Tree