Semester 3 Practice Questions In Epidemiology

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Semester 3 Practice Questions In Epidemiology - Quiz

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Questions and Answers
  • 1. 

    An outbreak of gastritis occurred on a cruise ship.  The data in the following table were obtained shortly after the outbreak, from a questionnaire completed by everyone on board the ship. What is the relative risk of developing gastritis from herring consumption?

    • A.

      0.5

    • B.

      2.0

    • C.

      2.3

    • D.

      8.0

    • E.

      1.0

    Correct Answer
    B. 2.0
    Explanation
    Relative risk (RR) = Risk in exposed/Risk in unexposed
    And, Risk = Number of cases (d)/ Total number of people at risk (N)

    Therefore, RR for developing gastritis from herring consumption = Risk in ‘Ate’/ Risk in ‘Did not eat’

    = (200/1000)/(100/1000)
    = 2.0
    NOTE: The risk can be calculated here because the total number of people who were at risk for falling ill is known. If the total number of people at risk of falling ill – say in a situation where a certain food chain is contaminated – then one cannot calculate risk but the odds of exposure is calculated instead (which should approximate the risk).

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  • 2. 

    In a study of 500 cases of a disease and 500 controls, the suspected etiological factor is found in 400 cases and 100 controls.  What is the absolute risk of disease in people with the factor?

    • A.

      80%

    • B.

      40%

    • C.

      16%

    • D.

      20%

    • E.

      Cannot be computed from the data given

    Correct Answer
    E. Cannot be computed from the data given
    Explanation
    Only odds can be calculated as a measure of incidence from case-control studies. In a case control study one is not sure about all the persons who had the particular exposure at the time in question and therefore the total number of persons at risk is unknown. Likewise, the duration of exposure to the risk factor in most instances and therefore rates cannot be calculated. The odds however gives a value that is numerically close to the risk.

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  • 3. 

    Regionville is a community of 100,000 persons.  During 1985 there were 1,000 deaths from all causes.  All cases of tuberculosis have been found and they total 300 – 200 males and 100 females.  During 1985, there were 60 deaths from tuberculosis, 50 of them males. What is the crude mortality rate for Regionville?

    • A.

      300 per 100,000

    • B.

      60 per 1,000

    • C.

      10 per 1,000

    • D.

      100 per 1,000

    • E.

      200 per 1,000

    Correct Answer
    C. 10 per 1,000
    Explanation
    The crude mortality rate it the death rate that is calculated using all deaths as the numerator and the total population as the denominator. Therefore
    Crude mortality rate = total deaths/total population
    = 1000/100,000
    = 10 per 1,000
    NOTE: Age-adjusted mortality rates are reported when population mortality statistics are calculated. This means that the mortality rate has been standardized against a ‘standard’ population to account for any differences in age-group distribution in the population from year to year.

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  • 4. 

    In 1945, there were 1,000 women who worked in a factory painting radium dials on watches.  The incidence of bone cancer in these women up to 1975 was compared to that of 1,000 women who worked as telephone operators in 1945.  Twenty of the radium dial painters and four of the telephone operators developed bone cancer between 1945 and 1975.  What study design is this?

    • A.

      Cohort study

    • B.

      Experimental study

    • C.

      Clinical trial

    • D.

      Cross-sectional study

    • E.

      Case-control study

    Correct Answer
    A. Cohort study
    Explanation
    The two groups where selected on the basis of the exposure (radium) and ‘followed’ over time (1945 to 1975) to see what the outcome experience (bone cancer) was. In fact because the investigators when back in time to establish the groups this study could also be called a retrospective cohort study (as compared to the usual prospective cohort study in which the groups are established in real time and followed up into the future.

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  • 5. 

    Researchers set out to demonstrate that a new drug is more effective in lowering systolic blood pressure than beta-blockers.  They select two groups from among a number of previously uncontrolled hypertensive patients to receive either the new drug or a beta-blocker using a computer programme to make the allocation purely by chance.  What is this method of assignment called?

    • A.

      Random selection

    • B.

      Randomization

    • C.

      Blinding

    • D.

      Cross-over

    • E.

      Factorial

    Correct Answer
    B. Randomization
    Explanation
    Randomization (or random allocation) is the method by which chance is used to allocate study participants to study groups. Random selection it the method by which chance (e.g. rolling dice or using a table of random numbers) is used to select participants for inclusion in a study. Blinding is where the participants are not aware whether they are receiving the intervention under investigation, current treatment or placebo. Cross-over is where one group in a cohort receives the intervention under study while the other receives current best treatment or placebo and then (following a wash out period) the groups switch around so that the group which was receiving placebo or current treatment now receives the intervention under evaluation. Factorial design is where a cohort study is set up to test more than one hypothesis at the same time so that the study group is randomized first to test one hypothesis and then those groups are randomized another time to create groups to test a second hypothesis.

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  • 6. 

    A screening test for breast cancer was administered to 400 women with biopsy-proven breast cancer and to 400 women without breast cancer.  The test results were positive for 100 of the proven cases and 50 of the normal women. What is the sensitivity of this screening test?

    • A.

      88%

    • B.

      67%

    • C.

      25%

    • D.

      33%

    • E.

      12%

    Correct Answer
    C. 25%
    Explanation
    Sensitivity = (# correctly positive on screening test / # positive on gold standard)x 100
    = (100/400) x 100
    = 25%
    NOTE: Validity (sensitivity, specificity etc.) questions are best answered by first setting up a 2x2 table before attempting to answer the question even if the answer seems to be obvious (so as to avoid simple errors). Make sure that your totals in the table are correct before you proceed with the calculation.

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  • 7. 

    A 25 year old male patient presents to you with a purulent urethral discharge for one day. He admits to having had unprotected sex 3 nights ago and has had no other sexual contact in the past year.  In order to initiate empirical treatment while awaiting laboratory tests for this sexually transmitted illness in this patient what other period do you need to know?

    • A.

      Period of exposure

    • B.

      Incubation period

    • C.

      Infectious period

    • D.

      Latent period

    • E.

      Serial interval

    Correct Answer
    B. Incubation period
    Explanation
    You need to know which is the most likely pathogen and therefore you need to know what are the incubation periods for organisms which cause urethritis. The latent and infectious periods would be useful to know when trying to establish whether any other individuals may have been infected by this patient.

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  • 8. 

    Researchers investigated the relationship between the use of statins and prostate cancer mortality by examining the records of patients who died from prostate cancer as well as records of matched controls. They report an unadjusted odds ratio of 0.49 (95% confidence interval, 0.34-0.70), which decreased to 0.37 (P<0.0001), after adjusting for education, waist size, body mass index, comorbidities and anti-hypertensive medication.  What can you conclude from these results?

    • A.

      Statins significantly lower the risk of death from prostate cancer

    • B.

      Statins have no effect on cancer mortality

    • C.

      Comorbidities have no effect on prostate cancer mortality

    • D.

      This was an ecological study

    • E.

      The sample size was too inadequate

    Correct Answer
    A. Statins significantly lower the risk of death from prostate cancer
    Explanation
    The unadjusted odds ratio has a 95% confidence interval that does not include 1 and the adjusted odds ratio is associated with a P-value of

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  • Current Version
  • Mar 22, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Jun 08, 2012
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    Rosssweetie
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