epidemiological methodology

Epidemiological methodology


Instructions: Please show all calculations. Your submission should be in a single PDF file.

  1. In an epidemic, an exposure source can be described as common exposure, point exposure, propagated exposure, or mixed exposure.
  2. Which source of exposure is described by the epidemic curve below, and why? (4pts)


  1. Give an example of the exposure source in the figure above. (2Pts)
    c. Outline four (4) useful information that can be derived from epidemic

curves. (4Pts)

  1. Consider the epidemic curve from an outbreak of Ebola (below). If the average incubation period for Ebola is 9 days (minimum of 2 days and

maximum of 21 days), determine the most likely period of exposure. (10Pts)


Ebola Cases by Date of Onset, Spring City, November 2015

  1. Discuss, with examples, the following terms as applied to screening tests: (10Pts)
    • Sensitivity
    • Specificity
    • Positive Predictive Value
    • Negative Predictive Value
  2. Tonometer, a screening test for glaucoma, measures intraocular pressure. Some people with glaucoma have intraocular pressures as low as 22 millimeters of mercury (mm Hg), while other people can have intraocular pressures as high as 27 mm Hg. Discuss the effect on sensitivity, specificity, false positive rate, and false negative rate, if ……
  • Diagnostic cut-point is set at 22 millimeters of mercury. (4Pts)
  • Diagnostic cut-point is set at 27 millimeters of mercury. (4Pts)
  • What should be the preferred diagnostic cut point, and why? (2Pts)
  1. Compare and contrast the following study designs in epidemiological methodology. (10Pts)
    • Cross-Sectionaldesign
    • Case-Control study design
    • Prospective Cohort study design
  2. (i) Discuss the importance of age-adjustment in epidemiology. (5Pts) (ii) Distinguish between direct and indirect age-adjustment. (5Pts)
  3. (i) Discuss, with examples, four (4) characteristics of diseases appropriate for screening. (4Pts)
    (ii) Discuss, with examples, six (6) characteristics of screening tests (4pts) (iii) Discuss the importance of disease prevalence in planning screening programs (2Pts)
  4. (i) What is confounding and why is it an important consideration in epidemiological studies? (6Pts)

(ii) Discuss four (4) approaches to control for confounding. (4Pts)

  1. Discuss, with examples, the following terms in the Hill’s Criteria for assessing causality. (10Pts)
  2. StrengthofAssociation b. Biological Plausibility c. Temporality
    d. Biological Gradient
  3. Consistency

10.Discuss the relationship between sample size and confidence interval, and their association with precision of epidemiological studies. (10Pts)

11.a. Define Vaccine Efficacy. (2Pts)
b. Calculate and interpret the vaccine efficacy of a new COVID-19


vaccine presented in the table below: (8Pts)


12.The table below presents results of a study investigating tobacco use and risk of hypertension:


Calculate and interpret the following: (10Pts)

  • Relative Risk (RR)
  • Attributable Risk (AR)
  • Attributable Fraction (AR %)
  • Population Attributable Risk (PAR %)

13.Hepatitis B virus (HBV) is suspected in many prison inmates. Only one screening test for HBV is available, and it is 88% sensitive, and 76% specific. If 1,000 prison inmates were screened using such a test, and the true prevalence of HBV infection in that population was 25%, calculate and interpret the following: (10Pts)

  1. Positive predictive value (PV+) b. Negative predictive value (PV-)

14.In a field study to investigate the effect of Alcohol consumption on hypertension, cases and controls were matched and data collected in pairs as shown in the table below: (10Pts)



Complete the follow table:


  • Calculate and interpret the Odds Ratio
  • Compute and interpret the 95% Confidence interval
  • Is the association between alcohol consumption and hypertension
    statistically significant? Explain.

15.Consider a hypothetical study in which an investigator enrolled 2600 subjects to compare subjects who had diabetes in the past year to subjects who have not had diabetes within the past year for history of alcohol consumption. (10Pts)

  • What type of study design is the investigator using?
  • Assume the following results: 2600 subjects were enrolled in the study. Of
    these subjects 220 who had diabetes also had a history of alcohol use. 60 subjects had diabetes but did not have a history of alcohol use. A total of 1080 subjects in the study had no history of alcohol use. Calculate the risk of having diabetes for subjects with a history of alcohol use compared with subjects without a history of alcohol use. [In other words, calculate either the odds ratio or relative risk, whichever is more appropriate, and interpret your result].
  • Calculate and interpret the 95% Confidence Interval for the risk estimate calculated above.
  • Is the risk estimate calculated above statistically significant? Explain.


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