Homework: PRINCIPLES OF EPIDEMIOLOGY
TOPIC: Measuring Morbidity: Prevalence and Incidence
Read the scenario below and complete the homework as instructed.
Scenario
In Community X (population 20,000), an epidemiologist conducted a prevalence survey in January of 2012 and reported an HIV prevalence of 2.2%. Over the next 12 months, the department of health reported an additional 50 new HIV cases between February 2012 and January 2013. The total population stayed constant at 20,000.
Part I
i. How many people had HIV in January 2012? Present or describe the formula you used to arrive at your answer.
ii. Calculate the incidence rate assuming no HIV-related deaths over the 12-month period. Present or describe the formula you used to arrive at your answer. Be sure to clearly indicate the numerator and denominator used in your calculation and include an appropriate label for the rate.
In a summary of 200 to 250 words, interpret the results and discuss the relationship between incidence and prevalence. Discuss whether or not the epidemiologist should be concerned about these new HIV infections, assuming a previous incidence rate of 0.5 per 1,000 person-years prior to this updated risk assessment.
Part II
A rapid test used for diagnosing HIV has a sensitivity of 99.1% and a specificity of 90%. Based on the population prevalence of 2.2% in 2012, create a 2x2 table showing the number of true positives, false positives, false negatives, and true negatives. Calculate the positive predicative value and negative predictive value for this test. Refer to the "Creating a 2x2 Contingency Table" resource for guidance.
In 200 to 250 words, discuss whether or not the epidemiologist should recommend this test as part of a universal HIV screening program. Provide rationale for your recommendation applying the positive and negative predictive values. Present or describe the formula you used to arrive at your answer.
Format your homework according to the following formatting requirements:
i) The answer should be typed, using Times New Roman font (size 12), double spaced, with one-inch margins on all sides.
ii) The response also includes a cover page containing the title of the homework, the student's name, the course title, and the date. The cover page is not included in the required page length.
iii) Also include a reference page. The Citations and references must follow APA format. The reference page is not included in the required page length.
Reference
Read Chapters 14 and 15 in Gordis Epidemiology.
Read "Association or Causation: Evaluating Links Between 'Environment and Disease,'" by Lucas and McMichael (2005), located on the World Health Organization website.
Read "Weak Associations in Epidemiology: Importance, Detection, and Interpretation," by Doll, from Journal of Epidemiology (1996).
Read "Causal Inference Based on Counterfactuals," by Hofler (2005), located on the BioMed Central website.
Read "Multicausality: Confounding," by Schoenbach (2004), located on the Epidemilog net website.
View "Sensitivity and Specificity - Explained in 3 Minutes," by Martin (2014), located on the YouTube website.
View "The Relationship Between Incidence and Prevalence," by Patwari (2013), located on the YouTube website.
Use the "Creating a 2x2 Contingency Table" resource to assist with the completion of the Measuring Morbidity: Prevalence and Incidence homework, as needed.