Every Rate Has a Denominator: Prevalence, Incidence, and Control of Hypertension in a Composite County, With Sources and Years
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Doctor of Nursing Practice Program, Aspen University
DNP875: Population Health and Person-Centered Care
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Month Day, Year
Every Rate Has a Denominator: Prevalence, Incidence, and Control of Hypertension in a Composite County, With Sources and Years
Population health decisions rest on rates, and rates are only meaningful when readers know what was counted, out of whom, when, and according to which source. This paper reports the prevalence, incidence, and control of hypertension in the composite Delmont County population defined in the previous module, with every figure accompanied by its numerator, denominator, year, and source. It then compares local and national figures and explains why direct comparison requires caution.
Prevalence and Incidence Defined
Prevalence is the proportion of a population that has a condition at a point or over a period of time; it reflects both how often new cases arise and how long people live with the condition. Incidence is the rate at which new cases occur in a population at risk over a defined period; its denominator excludes people who already have the condition (Celentano & Szklo, 2019). For a chronic condition like hypertension, prevalence describes the burden a health system must manage, while incidence describes how quickly that burden is growing and where prevention is needed.
Prevalence in the Clinical Population
In the collaborative's shared data for calendar year 2025, 97,800 adults aged 18 to 85 were attributed to a participating primary care practice. Of these, 24,610 met the project's hypertension definition and were not excluded, a period prevalence of 25.2 percent. This figure is crude, not age-adjusted, and it counts diagnosed or repeatedly elevated hypertension among people in care; it is lower than the national survey figure because it relies on clinical records rather than standardized measurement of every adult.
The county estimate from the state's 2024 behavioral risk factor survey, in which adults report whether a health professional has told them they have high blood pressure, was 34.1 percent of adults, with a denominator of the survey's weighted estimate of the county's adult population. The difference between 25.2 and 34.1 percent reflects different populations, definitions, and methods, not necessarily an error in either.
Incidence
Incidence was calculated among attributed adults who did not meet the hypertension definition at the start of 2025 and who remained attributed through the year: 71,950 adults at risk. Of these, 1,510 met the definition for the first time during the year, an annual incidence of 21.0 per 1,000 adults at risk. Incidence was highest among adults aged 45 to 64, at 32.4 per 1,000. Prevalence tells the collaborative how many people need care now; incidence tells it how many more will need care next year if nothing changes upstream.
Control
Of the 24,610 adults in the hypertension population, 14,360 had a last reading for 2025 that fell under 140/90 mm Hg, which puts control at 58.4 percent. Using the stricter threshold of below 130/80, 6,890 were controlled, 28.0 percent. Nationally, age-adjusted control among adults with hypertension, defined as below 140/90 in national survey data, declined to 43.7 percent in 2017-2018 (Muntner et al., 2020).
Why Local and National Figures Differ
The local control rate of 58.4 percent looks better than the national 43.7 percent, but the comparison is misleading without adjustment. The national figure comes from a survey that measures blood pressure in a standardized way in a representative sample, including people who do not know they have hypertension and people without regular care. The local figure includes only people in care, who are more likely to be diagnosed and treated, and uses clinic readings, which vary in technique. The years differ, and the local rate is not age-adjusted. The national task force estimates that hypertension affects about 45 percent of U.S. adults (US Preventive Services Task Force et al., 2021), far above the local clinical prevalence of 25.2 percent, which suggests that many county residents with hypertension are undiagnosed or outside the collaborative's practices.
The appropriate conclusion is not that Delmont County outperforms the nation, but that among people in care, a little over half have controlled blood pressure, and that an unknown number of residents with hypertension are not counted at all.
What the Figures Suggest for Action
Read together, the three measures point to different kinds of work. The gap between clinical prevalence and the survey estimate suggests that finding people with undiagnosed or untreated hypertension, for example through screening at community sites and outreach to residents without a regular clinician, could matter as much as improving care for those already known. The incidence figure, highest in middle age, points toward prevention in the years before hypertension develops, through attention to weight, physical activity, sodium, alcohol, and the conditions that shape them. And the control rate shows that roughly four in ten people already diagnosed and in care are not at goal, a group the collaborative can reach through its own practices. The next modules will examine who is most affected within each of these groups and why, before any intervention is chosen.
Reporting Standards for the Project
For the remainder of the project, every rate will be reported in the same format: numerator and denominator, the population and period, the definition used, the data source, and whether the figure is crude or adjusted. Rates for subgroups with fewer than 30 people will not be reported, and confidence intervals will be added for comparisons between groups. Age adjustment to the 2000 U.S. standard population will be applied when comparing the county with national data.
A Note on Trends
A single year of data cannot show whether things are improving. The collaborative's shared warehouse holds data from 2022 onward, so the project will also report prevalence and control for each of the four years, using the same definitions, to establish whether control was stable, rising, or falling before any intervention began.
Conclusion
In Delmont County's clinical population, hypertension prevalence was 25.2 percent, incidence 21.0 per 1,000 adults at risk, and control below 140/90 was 58.4 percent in 2025. Each figure depends on its denominator, definition, and source, and none can be compared with national survey estimates without accounting for those differences. Reporting rates with their full context makes the project's numbers trustworthy and prevents false reassurance.
References
Celentano, D. D., & Szklo, M. (2019). Gordis epidemiology (6th ed.). Elsevier.
Muntner, P., Hardy, S. T., Fine, L. J., Jaeger, B. C., Wozniak, G., Levitan, E. B., & Colantonio, L. D. (2020). Trends in blood pressure control among US adults with hypertension, 1999-2000 to 2017-2018. JAMA, 324(12), 1190-1200. https://doi.org/10.1001/jama.2020.14545
US Preventive Services Task Force, Krist, A. H., Davidson, K. W., Mangione, C. M., Cabana, M., Caughey, A. B., Davis, E. M., Donahue, K. E., Doubeni, C. A., Kubik, M., Li, L., Ogedegbe, G., Pbert, L., Silverstein, M., Stevermer, J., Tseng, C.-W., & Wong, J. B. (2021). Screening for hypertension in adults: US Preventive Services Task Force reaffirmation recommendation statement. JAMA, 325(16), 1650-1656. https://doi.org/10.1001/jama.2021.4987
How this DNP 875 Module 2 example is structured
DNP875 Module 2 papers typically report incidence and prevalence with sources, years and denominators. Aspen does not publish module deliverables, so check your classroom for the exact prompt. This example defines each measure, reports local figures with full context, compares them carefully with national data and sets reporting standards for the rest of the project.
DNP875 Module 2 questions, answered
What does DNP875 Module 2 usually ask for?
The module typically asks you to report the incidence and prevalence of a condition in your population, with sources, years and denominators, and to interpret them. Aspen does not publish module deliverables, so your classroom's instructions govern.
What is the difference between incidence and prevalence?
Prevalence is the proportion of a population with a condition at a point or period. Incidence is the rate of new cases among people at risk over a period, so its denominator excludes those who already have the condition.
Why can't local clinical rates be compared directly with national survey rates?
They differ in population, measurement method, definitions, years and age adjustment. Clinical data count only people in care, while national surveys measure a representative sample, including undiagnosed and untreated people.
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