In it the author, an epidemiologist, explains the difference between ‘numerator’ versus ‘denominator’ thinking and presents the data for SARS-CoV2 in children during the Omicron wave using this framework:
- Numerator thinking: A heavier lens on the absolute numbers—How many children are hospitalized? Is this number increasing? How many children have died?
- Denominator thinking: A heavier lens on the population in which the numerator arises—How many children have died compared to adults? How many myocarditis cases per 1,000,000 doses?
In other words, numerator thinkers focus on individuals and denominator thinkers focus on populations. Both perspectives are valid and important, but as we have seen with COVID-19 these different views can lead to intense disagreement.
The author states “One puts weight on each differently based on history, background, culture, employment, and context. For example, clinicians care for these patients every day, and the numerator is top of mind. As a parent, having my kid in the numerator is not comforting even if the probability of that happening was small. Policymakers, on the other hand, need a more denominator-oriented perspective.” As a clinician and a parent what the author says here rings true for me. For the numerator thinkers it tends to come down to individual risk tolerance while the denominator thinkers prioritize impact on populations of people.
The tension between numerator and denominator thinking is very apparent with COVID but it is also relevant to other areas of medicine, such as cancer screening. Specifically, I have been thinking about two common types of cancer screening through the numerator and denominator lenses: mammography for breast cancer and PSA testing for prostate cancer.
- My numerator thinking: The American Cancer Society estimates about 43,250 deaths from breast cancer and 34,500 from prostate cancer in 2022 in the United States. Some lives are saved with these cancer screening tests! There are important downsides to testing for an individual that are frequent such as false positives leading to worry, additional testing, possible biopsies, and complications from overdiagnosis and overtreatment
- My denominator thinking: With both of these cancer screening tests the number of people that would need to be screened in order to save a life is high
To try to reconcile the two perspectives I look to the evidence available and you, our patients, to help make the best decision for you. This is called shared decision making and it is the bread and butter of primary care medicine. It involves us providers sharing what we know about the risks and benefits of various interventions/tests and getting to know you and your risk tolerance for different outcomes so that you feel informed to make a decision.
Below I have built a table to help outline some of what we should take into consideration together when discussing mammography or PSA testing. The table includes recommendations from the United States Preventive Services Task Force (USPSTF), an independent, volunteer panel of experts in disease prevention and evidence-based medicine. The task force assigns a grade to their recommendation depending on the level of certainty that the net benefit of the preventive service is substantial (see key in the table), and the grade is associated with a suggestion for what to offer in practice. In the table I also included epidemiological data on these cancers, the number needed to screen in order to save a life, potential downsides of screening, and factors that increase a person’s risk of cancer. All of this should factor into any decision.
Bottom line: there is no one-size-fits-all approach and we are here to help you weigh the risks and benefits of tests and interventions in order to come to an informed decision. Ultimately, I come to the same conclusion as the author of the article: “We need to approach everyone’s decisions with empathy and recognize how (and why) people may put more emphasis on numerators or denominators.”
I would like to end by wishing you all a Happy Nowruz (or Persian New Year). Nowruz means ‘new day’ in Farsi and falls on the first day of spring. With the ongoing tragedy abroad and Spring just around the corner on March 20th I wanted to share a quote by Rumi on renewal:
“Every fragile beauty, every perfect forgotten sentence, you grieve their going away, but that is not how it is. Where they come from never goes dry. It is an always flowing spring.”
**Note, other societies have different recommendations for cancer screening. For example, the American Cancer Society recommends mammograms yearly from age 45 to 54 and then switching to every other year at age 55.
1. Jetelina, Katelyn. “State of Affairs: Pediatrics and Omicron.” Your Local Epidemiologist: Translating Public Health Science for Everyday Use. January 13, 2022
2. U.S. Preventive Services Task Force. Breast Cancer Screening Recommendations, 2016
3. U.S. Preventive Services Task Force. Prostate Cancer Screening Recommendations, 2018
4. American Cancer Society. Key Statistics for Breast Cancer. Last updated: January 2022
5. American Cancer Society. Key Statistics for Prostate Cancer. Last updated: January 2022
6. Taranto, N, Keating, NL, Williams PN, Brigham SK, Valdez I, Medford A, Watto MF. “#234 The Breast Lump, and Breast Cancer Screening”. The Curbsiders Internal Medicine Podcast. https://
7. Brody, Jane. “Debating the Value of PSA Prostate Screening.” New York Times. February 24, 2020.
Human and Environmental Health Spotlight:
Global warming can increase pollen levels (increased biomass and earlier bloom times). Pollen can be a major trigger for seasonal allergies and for asthma symptoms. Here are some tools to monitor pollen levels and manage asthma symptoms:
Spring also means that many of us are returning to our gardens or creating a garden for the first time. Gardens come in all shapes and sizes and can be an excellent way to mitigate climate crisis, learn more about the environment, and benefit mental health.
Sustainable Gardening tools:
Know your regions hardiness zone: https://planthardiness.ars.
Support pollinators with your plant choices: https://xerces.org/
publications/plant-lists/ pollinator-plants-maritime- northwest-region
Mulch your garden to decrease water use
Create drought tolerant landscaping: https://www.seattletimes.com/
explore/at-home/seattles- hotter-summers-call-for- landscaping-thats-drought- tolerant/
Learn how to grow your own groceries: https://mgfkc.org/education/
Happy Spring Equinox!
Wishing you improved allergy symptoms. As always, reach out with any questions.
Ali Gibbs, FNP student