| Course | HS340 Epidemiology |
|---|---|
| Unit | Unit 2 |
| Paper type | Rate calculation set |
| Length | About 760 words, 5 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | BS in Health Science |
| Updated | October 2026 |
Free sample paper for HS340 Unit 2
One Table, Seven Rates: A Unit 2 Rate Calculation Set on Kidney Failure in a Composite County of 300,000
[Student Name]
Purdue University Global
HS340: Epidemiology
Unit 2 Rate Calculation Set
[Instructor Name]
[Date]
The county and its counts are composite and chosen for arithmetic; the methods sources and the national data system named are real.
The Table
Mid-year population: [300,000]. New cases of end-stage kidney disease, meaning people who began dialysis or received a kidney transplant for the first time during the year: [120]. People living with end-stage kidney disease on January 1: [600]. People living with end-stage kidney disease on December 31: [630]. Deaths during the year among people with end-stage kidney disease: [90]. Deaths in the whole county with kidney failure recorded as the underlying cause: [30]. Residents aged 65 to 74: [30,000]; new cases in that age group: [45].
A quick check holds the table together: [600] at the start, plus [120] new cases, minus [90] deaths, gives [630] at year end.
Problem 1. Incidence Rate
The year's new starts over the mid-year population: 120 divided by 300,000, times 100,000, equals 40.0 new cases per 100,000 residents per year. The mid-year population stands in for person-time, a common approximation when the count of people already on treatment is small relative to the population (Centers for Disease Control and Prevention [CDC], 2012). The rate can be compared with the national incidence published in the US Renal Data System's annual report (United States Renal Data System, 2024).
Problem 2. Point Prevalence at Year End
People living with the condition on one date, divided by the population: 630 divided by 300,000, times 100,000, equals 210.0 per 100,000 on December 31. Prevalence is a proportion, not a rate, because it has no time in its denominator.
Problem 3. Period Prevalence for the Year
Anyone living with kidney failure on any day of the year: the [600] already living with it plus the [120] new cases, or 720. Divided by 300,000, times 100,000: 240.0 per 100,000. Period prevalence is higher than either point prevalence because it counts people who died during the year as well as those who started treatment.
Problems 2 and 3 use almost the same people and give different answers, because each answers a different question: how many on one day, and how many at any time in the year.
Problem 4. Death Rate Among People With the Condition
Deaths among people with the condition, divided by the average number living with it: the average of [600] and [630] is 615. Then 90 divided by 615 equals 0.146, or 146.3 deaths per 1,000 people with kidney failure per year. This is a case-group mortality rate and must not be compared with any death rate for the whole county, since its denominator is a small, very ill group.
Problem 5. Cause-Specific Mortality Rate
Deaths with kidney failure as the underlying cause, divided by the whole population: 30 divided by 300,000, times 100,000, equals 10.0 per 100,000 per year. Most of the [90] people with kidney failure who died had another underlying cause on the certificate, often heart disease, which is why Problems 4 and 5 use different numerators as well as different denominators.
Problem 6. Age-Specific Incidence Rate
New cases aged 65 to 74 divided by residents aged 65 to 74: 45 divided by 30,000, times 100,000, equals 150.0 per 100,000 per year. That is nearly four times the all-ages rate of 40.0, which is why crude rates from counties with different age structures cannot be compared directly without age adjustment (Celentano & Szklo, 2019).
Problem 7. Proportion of New Cases in One Age Group
New cases aged 65 to 74 divided by all new cases: 45 divided by 120 equals 37.5 percent. This is a proportion of cases, not a rate. It says what share of new patients are in that age group, not how likely a person in that age group is to become a case. A reader who saw 37.5 percent and concluded that older adults rarely develop kidney failure would be confusing the two.
Summary of Results
Incidence, 40.0 per 100,000 per year. Point prevalence at year end, 210.0 per 100,000. Period prevalence, 240.0 per 100,000. Deaths among people with the condition, 146.3 per 1,000 per year. Cause-specific mortality, 10.0 per 100,000 per year. Incidence at ages 65 to 74, 150.0 per 100,000 per year. Share of new cases aged 65 to 74, 37.5 percent. Every figure names its numerator, its denominator and its year, so a reader could recompute it from the table.
References
Celentano, D. D., & Szklo, M. (2019). Gordis epidemiology (6th ed.). Elsevier.
Centers for Disease Control and Prevention. (2012). Principles of epidemiology in public health practice: An introduction to applied epidemiology and biostatistics (3rd ed.). U.S. Department of Health and Human Services.
United States Renal Data System. (2024). USRDS annual data report: Epidemiology of kidney disease in the United States. National Institute of Diabetes and Digestive and Kidney Diseases. https://usrds-adr.niddk.nih.gov
The Purdue Global HS340 Unit 2 instructions
The second unit typically supplies a table of counts and asks for a set of rates and proportions, with the working shown. Expect five to ten problems on two to four pages. Instructors look for the correct numerator and denominator for each measure, the right multiplier, units written out in words and a short note on what each figure means. Many sections test whether you can tell incidence from prevalence, a rate from a proportion and a case-group death rate from a population death rate. Show each step in a sentence, round only at the end, and check that the table's numbers agree with each other before you begin. Citing an epidemiology text for definitions usually earns credit.
How the HS 340 Unit 2 example is put together
The set restates the table first: population, new cases, people living with the condition on two dates, deaths among them, deaths with kidney failure as the cause and an age band. A one-line check confirms that the starting count plus new cases minus deaths equals the year-end count. Seven numbered problems follow, each with its formula in words, the arithmetic and a sentence on meaning. The highlighted sentence explains why two prevalence figures differ. Notes warn that the case-group death rate cannot be compared with any county-wide rate, that age-specific rates explain why crude rates need adjustment and that a proportion of cases says nothing about risk. A summary lists all seven results with units.
HS340 Unit 2 rubric: what earns full points
Rate sets tend to earn points for correct calculation, correct choice of numerator and denominator, clear labeling of units and time, interpretation and presentation of the working. Correct choice of denominator usually weighs most, since the right arithmetic on the wrong population still gives a wrong answer. Calculation credit is lost for rounding too early or using the wrong multiplier. Labeling is rewarded when every figure states per how many people and over what period. Interpretation earns points when a sentence explains what each measure means and does not mean. Presentation covers the working shown step by step. A set that checks its table for consistency before calculating shows care that graders notice.
Common HS340 Unit 2 mistakes, and how to avoid them
The commonest error is dividing deaths among people with a disease by the whole population, which turns a case-group rate into a misleading population figure. Another is calling prevalence a rate, or forgetting that period prevalence counts people who died during the year. Some students report a proportion of cases as if it described the risk in that group. Others round each step and drift away from the expected answer. Leaving out units makes even a correct number hard to grade. If your table covers a different condition, perhaps diabetes, HIV or cancer, share the counts with us, and each problem can be matched to its measure and label the answers properly.
Get an HS340 Unit 2 example written to your instructions
Send the population table the HS340 Unit 2 set supplies, the numbered questions and the rubric. A free first custom sample comes back within 24-48 hours with every problem set up the same way, the base of each rate named in a full sentence, plus one sentence on how the reporting program could use each result. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
More HS340 papers and BS in Health Science samples
- HS340 Unit 1: Surveillance Discussion Post
- HS340 Unit 3: Study Design Appraisal
- HS340 Unit 4: Two by Two Table
- HS340 Unit 5: Bias and Confounding Memo
- HS340 Unit 6: Outbreak Investigation Writeup
- HS340 Unit 7: Seminar Reflection
- HS340 Unit 8: Screening Test Analysis
- HS340 Unit 9: Surveillance Data Review
- HS340 Unit 10: Epidemiology Case Report
- HS315 Unit 2: Community Health Profile
- HS305 Unit 2: Research Article Summary
- HS292 Unit 2: Gout Visit Record Abstraction
- HS450 Unit 2: Environmental Scan
HS340 Unit 2 questions, answered
Which population goes under a death rate for people with a disease?
The people who have the disease, because only they can die with it in the sense the rate measures. Use the count at the start of the period, or a mid-period estimate, and say which. Dividing those deaths by the whole county produces a different measure, closer to cause-specific mortality, and mixing the two is one of the most frequent errors on this unit.
How many decimal places should the answers carry?
One decimal place per 100,000 or per 1,000 is conventional for rates of this size, and percentages usually take one as well. Round only at the final step, since rounding intermediate values can shift later answers. The example keeps full precision through each calculation and rounds only when it reports a result, so a grader recomputing any problem lands on the same figure.
Where can I find a free HS340 Unit 2 sample paper?
You can read the full Unit 2 rate calculation set here, seven measures worked from one table on kidney failure in a composite county.
How do point prevalence and period prevalence differ?
Point prevalence counts people with a condition on one date. Period prevalence counts everyone who had it at any time during an interval, including those who died or recovered.
Is incidence a rate or a proportion?
Incidence rate has time in its denominator, such as per 100,000 per year. Cumulative incidence, the share of a group who develop a condition over a period, is a proportion.