VetZone vet zone dog cat veterinary medicine veterinarian technician tech health CE continuing education preventive diplomate ACVPM DACVPM health prevalence incidence biostatistics what is the difference between simple for dummies

Incidence and Prevalence

When flipping through a news article involving infectious disease, it’s likely you have some across the terms of incidence and prevalence. “There is an alarming rise in prevalence for Disease XYZ in recent years” the story might say to hone your interest. The article might warn you without any specific numbers, but both terms have clear and distinct mathematical definitions. Let’s review these terms!

Podcast: Free Audio File

If you prefer to listen to podcasts, feel free to play the audio version of this blog by clicking on the player above.

Podcast: What Is the Prevalent Incidence That I Will Understand Biostatistics?
Length: 3 min 39 seconds
Written and read by the author

VetZone vet zone dog cat veterinary medicine veterinarian technician tech health CE continuing education preventive diplomate ACVPM DACVPM health prevalence incidence biostatistics what is the difference between simple for dummies

Defining Incidence and Prevalence

Incidence is a rate, and as such, it measures risk. We calculate it by taking as the number of new cases of disease and dividing it by the population at risk over a given period of time. Incidence answers the question, “how fast?”

Prevalence is a ratio and measures burden. We divide the total number of individuals with the disease by the total population at a specific point in time. Prevalence answers the question “How much?”

VetZone vet zone dog cat veterinary medicine veterinarian technician tech health CE continuing education preventive diplomate ACVPM DACVPM health prevalence incidence biostatistics what is the difference between simple for dummies

What incidence and prevalence data do we have in veterinary medicine?

From the standpoint of small animal veterinary medicine, we do not have the denominators. Without the resources, small animal medicine often fails to capture the figures of total population and the defined population at risk. And without denominators, true prevalence and incidence values remain elusive specters. Like ghosts in our peripheral vision, we recognize the presence of threat but struggle to properly quantify it. The numbers rematerialize with livestock and then vanish again into the mists of speculation with many wildlife scenarios.

VetZone vet zone dog cat veterinary medicine veterinarian technician tech health CE continuing education preventive diplomate ACVPM DACVPM health prevalence incidence biostatistics what is the difference between simple for dummies

The bathtub analogy for Incidence and Prevalence

The bathtub analogy provides clarity to the relationship between these two terms. The water in the tub describes the current number of cases and represents the prevalence. New cases pouring into the bathtub would be incidence. The water leaving the tub via the drain represents either patients that were cured or cases that died.

Vetzone vet zone dog cat veterinary medicine veterinarian technician tech health CE continuing education garlic onion sulfide sulphide sulfoxide sulphoxide leek shallot allium toxicity anemia Heinz body red blood cell flea unappetizing repellent holistic

Examples for thought

Like a jigsaw puzzle, incidence and prevalence represent tiles that help fit in with those of the disease process, available diagnostics, treatments, and preventions in place. With a more complete picture, we then interpret the numbers and learn that a dramatic rise in a number doesn’t always indicate a problem. For example, imagine that the advent of a new diagnostic test allows for much earlier diagnosis of a disease. As doctors begin using the test, they start diagnosing many more patients with this disease and consequentially, both the incidence and prevalence rise.

In another example, think of a deadly chronic disease where a new treatment comes along. The incidence may not change, but the prevalence will dramatically rise from the increased survival times of the patients.

VetZone vet zone dog cat veterinary medicine veterinarian technician tech health CE continuing education preventive diplomate ACVPM DACVPM health prevalence incidence biostatistics what is the difference between simple for dummies

Clarity through breadth

Neils Bohr said, “Clarity through breadth.” When looking at actual prevalence and incidence data, we must take the entire picture into view. In biostatistics, these two values form a background from which we can define other values such as positive predictive value, attack rate, and relative risk. Collectively, these direct medicine and even our individual actions towards a safer existence.

1
Leave a Reply

avatar
1 Comment threads
0 Thread replies
0 Followers
 
Most reacted comment
Hottest comment thread
1 Comment authors
VetZone Recent comment authors

This site uses Akismet to reduce spam. Learn how your comment data is processed.

  Subscribe  
newest oldest most voted
Notify of
VetZone
Admin

Thank you for reading our post and for the feedback. I am glad that it was both helpful and amusing. This was our goal. You can reach both myself and Dr. Wells at myvetzone@gmail.com. We look forward to hearing from you.