Exercise 3.2 You are working in a community hospital in a small town in Tennesse
ID: 3202099 • Letter: E
Question
Exercise 3.2
You are working in a community hospital in a small town in Tennessee. The town’s population is 23,000. There were six cases of Rocky Mountain spotted fever diagnosed in the past year.
Calculate the incidence of Rocky Mountain spotted fever per 1,000 and per 100,000.
Exercise 3.3
A rapid screening test for women with HPV (human papillomavirus) is being evaluated for its effectiveness and sensitivity as a screening test in college healthcare clinics. In order to determine the effectiveness of the HPV test, it was administered to 2,000 female college students. Tests were confirmed by comparisons to the gold standard test (Pap smears). Prevalence of HPV was 12% in the female college population; 352 students tested positive for HPV. The HPV test was found to be 92% specific. Create a 2 x 2 table that accurately describes this test and use this information to answer the following questions.
HPV
No HPV
Total
+ Test
Test
Totals
What is the sensitivity of this test?
What is the positive predictive value of this test?
What is the negative predictive value of this test?
If everything else remained the same, what would happen to the predictive value of a positive test if the disease prevalence increased in the population?
How many false negatives are there with this test?
How many false positives are there with this test?
Explain how false positives and false negatives can affect your patient population.
If the gold standard test (Pap smear) has a sensitivity of 94% and a specificity of 88%, which test (the new HPV test or Pap test) would you prefer to use in your healthcare clinic if you want to reduce the number of false-negative test results in your clinic? Which test would you prefer if you want to reduce the number of false-positive test results? Explain your answer using the results from previous calculations.
Exercise 3.4
AS investigators samples a groups of clients from a clinic based on their disease status---in particular, whether or not they have HTN. Of the 250 people sampled, 40% were found to have HTN. Knowing their disease status, a questionnaire is administered to the people in the study to determine how many have a family history (FHx) of stroke (in a first-degree relative). Of the people without HTN, 8% had a FHx of stroke. Of the the people with HTN, 37% had a FHX of stroke. Create a 2 x 2 table using this information and answers the following questions.
HTN
No HTN
Totals
+ FHx stroke
FHx stroke
Totals
What type of study design is this?
Can you calculate RR (relative risk using the data? Why or why not)
Can you calculate OR (odds ratio) using the data?
Calculate the correct descriptive statistics for this study (either RR or OR)
What is the correct interpretation of the statistic used?
Patients with a FHx of stroke are 6.75 times more likely to develop HTN than patients with no FHx of stroke.
Patients with HTN are 6.75 times more likely to have a FHx of stroke than those with normal blood pressure.
What are possible errors that could be made in this type of study?
Exercise 3.5
A study is conducted at your hospital to learn about the relationship between HIV and intravenous (IV) drug usage. You identify patients from your emergency department who are IV drug users and those who are note and follow then for 1 year. During that year, you identify 69 cases of HIV out of 253 who are IV drug users, and there are 17 new cases of HIV out of 450 who are not IV drug users. (The overall rate in both groups combined = 86 cases of HIV out of 703.). You are interested in developing an intervention to reduce the incidence of HIV and you would like to target a prevention program addressing risk factors. Create a 2 x 2 table using this information and the following questions.
+ HIV
HIV
+ IV drug use
IV drug use
Totals
Calculate the incidence rate of HIV in the IV drug users (Iexp), in the non-IV drug users (Inonexp), and overall (I). Express all rates as “per 1,000.”
What type of study design is this?
Calculate the relative risk (RR) for this exposure.
Calculate the attributes (AR) for this exposure. Interpret this result.
Calculate the AR proportion for this exposure. Interpret this result.
What are some problems that may be associated with this kind of study design?
What are possible confounders?
HPV
No HPV
Total
+ Test
Test
Totals
Explanation / Answer
(3.2) Let the incidence be x
(a) 6/23000 = x/1000
x = 6 * 1000/23000 = 0.261
(b) 6/23000 = x/100000
x = 6 * 100000/23000 = 26.09
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