What was the prevalence of TB in the screened community on January

Epidemiology Questions

Question 1

The following information applies to questions 1-4.

In January 2000 you began a one-year study of tuberculosis (TB) in a subsidized housing community in the Lower East Side of New York City. You enrolled 500 residents in your study and checked on their TB status on a monthly basis. At the start of your study on January 1st, you screened all 500 residents. Upon screening, you found that 20 of the healthy residents were immigrants who were vaccinated for TB and so were not at risk. Another 30 residents already had existing cases of TB on January 1st. On February 1st, 5 residents developed TB. On April 1st, 5 more residents developed TB. On June 1st, 10 healthy residents moved away from New York City were lost to follow-up. On July 1st, 10 of the residents who had existing TB on January 1st died from their disease. The study ended on December 31, 2000. Assume that once a person gets TB, they have it for the duration of the study, and assume that all remaining residents stayed healthy and were not lost to follow-up.

What was the prevalence of TB in the screened community on January 1st?


50/500, or 10%

30/500, or 6%

20/450, or 4.4%

30/450, or 6.7%

Question 2

What was the prevalence of TB on June 30th?


10/450, or 2.2%

10/500, or 2%

40/500, or 8%

40/490, or 8.2%

Question 3

What was the cumulative incidence of TB over the year?


10/450, or 2.2%

40/500, or 8%

10/480, or 2.1%

40/450, or 8.9%

Question 4

What was the case-fatality rate among residents with TB over the course of the year?


10/500, or 1.02%

10/40, or 25%

10/30, or 33%

10/450, or 2.2%

Question 5

The purpose of double blinding in clinical trials is to:


Reduce error that results from how the outcome is assessed

Reduce error that results from subject’s participation in the trial

Reduce error that results from assignment to study conditions

The 1st and 3rd answers only

All of the above

Question 6

An analysis that includes all subjects who were randomized to the treatment and comparison groups, regardless of whether they received or completed their assigned study protocol.


Run-in period

Efficacy analysis


Intent-to-treat analysis

Question 7

The ideal comparison group in a cohort study


Is as similar as possible to the exposed group with respect to factors other than the exposure that could influence the development of disease.

Would, if possible, consist of exactly the same individuals in the exposed group had they not been exposed.

Both of the above

Neither of the above

Question 8

Noncompliance in an experimental study biases the results toward the null.




Question 9

The following information applies to questions 9 and 10.

A study was done to determine whether the amount of money spent on soft drinks was related to mortality from diabetes. The investigators collected data on per capita (average per person) soft drink consumption in 10 U.S. states and examined its relationship to mortality rates from diabetes in those 10 states. In order to calculate per capita sales, they gathered annual data on soft drink sales from commerce records and then divided these figures by the state’s population from the most recent Census. The mortality data were gathered from the vital records department in each state. Here are the data that they collected.

U.S. State

Annual Per Capita Soft Drink Sales

Annual Diabetes Mortality Rate (per 100,000 population)




New York






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