Epidemiology: Measuring and Comparing Disease Frequencies

Individual exercises

  1. A population P considered to be high-risk for malaria has 10,000 members. Over a specified time period, 10 of these members contract malaria. What is the cumulative incidence of malaria in this population over this time period?
  2. A study is conducted on the contraction of HIV in Cape Town, South Africa. The Groote Schuur hospital is located near the central business district of the city, and at the time of the study approximately 60,000 residents live nearby and rely on its services. Among these residents, a subgroup of 4,000 members have been identified by the local government as being currently healthy but with high-risk for HIV infection. The study monitors these high-risk residents from the period between 1st July 2009 and 13th August 2010 and finds over this time period that 30 people contract the disease.
    1. In epidemiology terms, what type of population is the group of 60,000 residents who live near the Groote Schuur hospital?
    2. What type of population is the second group, the 4,000 high-risk members?
    3. When calculating the cumulative incidence of HIV in this study which population should we consider? In one sentence justify your answer
    4. Based on your answer to (c) calculate the cumulative incidence of HIV in this study.
  3. A study follows a group of people over the time period 1st September 2001 till 1st January 2002 (the 1st January is not included in the study time period). A member of this group, A, is followed throughout the entire time period of the study.
    1. Calculate the duration of the entire study time period. Present your answer in days.
    2. Hence state the person time accrued by A in this study
    3. A second group member, B, passes away on the 14th October 2001. Calculate the person time accrued in this study by member B. Present your answer in days.
    4. What is the person time accrued by both A and B together?
  4. A study on road accidents in Kumasi is conducted from 2nd February 2018 to 12th of March 2019. The study group has 5 members. Member A joins the study at the start and remains a member till the end. Member B joins the study at the start but then moves away from the area on the 23rd May 20018 and loses contact with the researchers. Member C joins the study late, on the 29th March 2019, and then dies in a car accident on the 9th January 2019.
    1. Calculate the duration of the study time period, in days
    2. Calculate the person time accrued by person C
    3. Calculate the total person time accrued by the whole study group over the time period of the study.
  5. A study group identified to be high-risk for disease X is followed for a duration of 190 days. The person time accrued by all group members together is 190 days, and over the course of the study, 20 group members contract disease X. Calculate the incidence rate, as estimated by this study, of disease X from this data.
  6. A population defined as the set of all sex workers currently working in Nairobi, Kenya, is identified by a study research team as being a high-risk population for HIV contraction. At the time of the study the size of this population is not known. A study on HIV is conducted for this population from 1st January 2020 till 1st July of the same year. Participants are recruited on the basis that they are currently employed in sex work as their primary work, and they have no history of HIV at the time of recruitment. The study recruits 10 members in total. Of these, 8 members make it till the end of the study without infection, and without losing contact with the study researchers. One member contracts HIV on the 16th of March that year. Another member moves away from Nairobi on the 6th June the same year.
    1. Calculate the duration of the time period of the study, in days.
    2. Calculate the total person time accrued by the study group throughout the study.
    3. Estimate the incidence rate of HIV in the study population over the study time period using the study data given above.
    4. If the study group was much larger, what would happen to the estimate of the incidence rate?
  7. A population \(P\) is known to have members struggling with type 2 diabetes. A population-wide survey is conducted in a single day whereby the size of the population is estimated to be 50,000 and the number of people in \(P\) suffering from diabetes is estimated to be 1,000. Calculate the point prevalence of type 2 diabetes in \(P\) on this day using this data.