Before the First Number: Defining the Population of Adults With Hypertension in a Composite County for a Population Health Project
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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
Before the First Number: Defining the Population of Adults With Hypertension in a Composite County for a Population Health Project
Population health work often begins with a statistic, such as the proportion of adults whose blood pressure is controlled. But every statistic depends on who is counted in the numerator and the denominator, and different definitions of the same population can produce very different numbers. This paper defines, before any figure is reported, the population for a DNP project on hypertension control in a composite county, explains each inclusion and exclusion rule, and shows how the choices affect what the project will measure and whom it will serve.
What Population Health Means Here
In the definition offered by Kindig and Stoddart (2003), population health concerns how healthy a defined group of people is and how that health is spread across the group, and the group itself can be drawn by place or by some other shared feature, such as a health plan or an employer. The definition has two practical consequences for this project. First, the project must decide whether its population is geographic, all adults with hypertension living in the county, or clinical, those attributed to a set of primary care practices. Second, the distribution of outcomes within the population, not only the average, is part of what is being measured.
The Setting
Delmont County, a composite setting, has roughly 180,000 people living in it, with a small city and surrounding rural townships. Three health systems provide most primary care: a hospital-owned network, a federally qualified health center with four sites, and a group of independent practices. The DNP project is sponsored by the county's population health collaborative, which includes all three.
Geographic or Clinical?
A geographic population would include every adult resident with hypertension, including those who have no regular source of care. It is the population the county health department is responsible for, but it cannot be counted directly from clinical records; estimates would come from surveys. A clinical population includes adults with hypertension who are attributed to one of the collaborative's primary care practices, meaning a primary care clinician in the collaborative saw them at least once during the preceding two years. It can be counted from electronic records and linked to blood pressure readings, but it excludes people without regular care, who are likely to have worse control. A clinical definition makes the problem measurable and hides part of it at the same time.
The project will use the clinical population as its primary population, because its interventions will be delivered through the practices and measured with their data, and will report a geographic estimate from county survey data alongside it, so that people outside care remain visible.
Who Has Hypertension?
The definition of hypertension itself is a choice. Under the 2017 national guideline, readings from 130/80 up to 139/89 mm Hg are stage 1 hypertension and 140/90 or above is stage 2 (Whelton et al., 2018), while many quality measures still use 140/90 as the threshold for control. For inclusion, the project will count adults with a hypertension diagnosis on the problem list or in encounter diagnoses during the measurement period, or with two or more outpatient readings of 140/90 or higher on separate days. Using diagnosis codes alone would miss undiagnosed patients with repeatedly high readings; using readings alone at 130/80 would include many people never evaluated or treated, whose inclusion would sharply lower the measured control rate.
Age and Exclusions
The population includes adults aged 18 to 85, matching the age range used in the widely reported measure of controlling high blood pressure, which allows comparison with other organizations. Exclusions are patients who are pregnant during the period, because hypertension in pregnancy is managed differently; patients receiving dialysis or with end-stage kidney disease; and patients enrolled in hospice or palliative care, for whom tight blood pressure targets may not be appropriate. Each exclusion is small in number but important for fairness, because including these patients would count as failures situations in which a lower target is not the goal of care.
The Denominator and the Numerator
The resulting denominator is adults aged 18 to 85, attributed to a collaborative practice, meeting the hypertension definition, and not excluded. The numerator for the primary outcome, controlled blood pressure, will be those whose last recorded reading of the measurement year fell under 140/90 mm Hg, with a secondary measure using below 130/80. Across the country, blood pressure control among adults with hypertension fell from 2013-2014 to 43.7 percent in 2017-2018, according to national survey data (Muntner et al., 2020); the project's local figure will be comparable only if definitions are stated this precisely.
Distribution Within the Population
Because population health includes the distribution of outcomes, the population will be described by age, sex, race and ethnicity, preferred language, insurance, and township of residence before any rate is calculated. Subgroups will be large enough to report only if they include at least 30 people, to avoid unstable rates. This structure prepares the project to identify disparities rather than reporting a single average that hides them.
Data Sources and Their Limits
The definition also determines which data sources the project can use. Clinical data will come from the three health systems' electronic records, extracted through the collaborative's shared data warehouse, which already matches patients across systems to avoid counting anyone twice. Blood pressure readings will be taken from outpatient visits only, because readings during hospital stays or emergency visits reflect acute illness. The county estimate for people outside care will come from the state's behavioral risk factor survey, which reports self-reported hypertension and treatment but not measured control. Each source has limits: clinic readings may be affected by technique and by patients rushing in late, and survey data depend on recall. The project will describe these limits alongside its results, so that readers understand what each figure can and cannot show.
Conclusion
Defining the population for a hypertension project involves choices about geography, clinical attribution, the definition of hypertension, age limits, exclusions, and subgroups, each of which changes the numbers the project will report. Stating these choices before calculating any figure makes the project's results interpretable, comparable, and honest about who is and is not counted.
References
Kindig, D., & Stoddart, G. (2003). What is population health? American Journal of Public Health, 93(3), 380-383. https://doi.org/10.2105/AJPH.93.3.380
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
Whelton, P. K., Carey, R. M., Aronow, W. S., Casey, D. E., Collins, K. J., Dennison Himmelfarb, C., DePalma, S. M., Gidding, S., Jamerson, K. A., Jones, D. W., MacLaughlin, E. J., Muntner, P., Ovbiagele, B., Smith, S. C., Spencer, C. C., Stafford, R. S., Taler, S. J., Thomas, R. J., Williams, K. A., ... Wright, J. T. (2018). 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults. Journal of the American College of Cardiology, 71(19), e127-e248. https://doi.org/10.1016/j.jacc.2017.11.006
How this DNP 875 Module 1 example is structured
DNP875 Module 1 samples often define a population precisely before any figure appears. Aspen does not publish module deliverables, so check your classroom for the exact prompt. This example defines population health with a source, weighs geographic and clinical definitions, specifies the case definition, exclusions, denominator and numerator with reasons and plans how the distribution within the population will be described.
DNP875 Module 1 questions, answered
What does DNP875 Module 1 usually ask for?
The first module often asks you to define the population for your population health work precisely, including inclusion and exclusion criteria, before reporting any statistics. Aspen does not publish module deliverables, so your classroom's instructions govern.
What is population health?
Kindig and Stoddart described it as the health of a defined group of people and the way that health is distributed within the group, where the group may be defined by place or by another shared feature.
Why does the population definition matter so much?
Different definitions of the numerator and denominator can produce very different rates. Choices such as clinical versus geographic populations or the blood pressure threshold used can change who is counted and what the measure shows.
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