Prevalence vs Risk: How Epidemiologists Count Disease Right

Prevalence vs Risk: How Epidemiologists Count Disease Right is Lesson 1 of 20 in Principles of Epidemiology. Ten percent of whom, and when? This lesson teaches the four kinds of numbers epidemiologists use, how prevalence differs from risk, and why the population at risk decides every denominator, all with the invented figures of Oakhaven Health District. This course is taught by Angel Reyes, MPH, MCHES, PMP, PMI-ACP, a doctoral candidate in public health who earned an MPH from a CEPH-accredited program, has planned, managed, and evaluated public health programs, and builds research training for graduate students and practitioners at Subthesis. Part of the 20-lesson course Principles of Epidemiology. Five key facts from this lesson: 1. Every health measure is a count, a ratio, a proportion or a rate, and you tell them apart by the numerator and the denominator. 2. Prevalence counts existing cases at a point or over a period; risk counts new cases among people who were free of the disease at the start. 3. In the invented example, 12,000 of Oakhaven's 100,000 residents have the condition on January 1, a point prevalence of 12 percent. 4. The population at risk excludes anyone who already has the outcome or cannot get it, and getting it wrong changes every incidence figure. 5. Attack rate, prevalence rate and case fatality rate are proportions despite their names, because none of them has time in the denominator. Free research tools at https://www.subthesis.com, including the Research Question Builder and the Statistical Power Calculator. Companion courses on this channel: Certified in Public Health: The CPH Exam Pathway, and Foundations of Program Planning. Examples are fictional and all figures are invented for teaching. Oakhaven Health District does not exist. This course is independent educational content from Subthesis and is not clinical, diagnostic, screening, or policy guidance.