1

Suppose that you began a one-year study of tuberculosis (TB) in a subsidized housing community in the Lower East Side of New York City on January 1st, 2010. 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, 2010. 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.

• Is the subsidized housing community in the Lower East Side of New York City a dynamic or fixed population? Briefly explain the rationale for your answer.
• What was the prevalence of TB in the screened community on January 1st?
• What was the prevalence of TB on June 30th?
• What was the cumulative incidence of TB over the year?
• SupposethatyouwantedtocalculatetheincidencerateofTBinthestudypopulation.Calculatetheamountofperson-timethatwouldgointhedenominatorofthisincidencerate.Besuretoshowyourwork.

QUESTION 2

1. Suppose that you are following a group of children for the development of asthma over a one- year period. You identify 100 children on January 1st, screen them for asthma, and set up a monitoring program to check on their status on a monthly basis. Five children are considered prevalent cases because they were diagnosed with asthma before January 1st. Ten children develop asthma on March 1st and another ten children develop asthma on July 1st. Another 10 children who remain healthy were followed for six months and then were lost to follow-up. All of the remaining children did not develop asthma and were not lost to follow-up. Follow-up ended on December 31st.

   • What was the prevalence of asthma on June 1st?
   • What was the prevalence of asthma on September 1st?
   • How many person-months of observation were accrued by this population?
   • Whatwastheincidencerateofasthmainthispopulationfortheone-yearperiod?

QUESTION 3

1. How does each of the following conditions influence the prevalence of a disease in a population? For each scenario, assume that no other changes occur. Your choices are: increases prevalence, decreases prevalence, or has no effect on prevalence.

   • A treatment is developed that prolongs the life of people suffering from the disease
   • A new measure is developed that prevents new cases of disease from occurring
   • There is immigration of a large number of healthy people into the population.
   • The case-fatality rate for the disease increases

-- Font family --

-- Font size --