Calculation Exercise

Nov 4th, 2015
Anonymous
Category:
Science
Price: \$15 USD

Question description

Calculation Exercise – Measures of Risk

A team of Epidemic Intelligence Service officers from the CDC arrives in Rhode Island to assist the state health department with investigation and control of an outbreak of measles.  The team is asked to include the entire state in the investigation; thus, the case definition for measles in this outbreak is any resident of Rhode Island meeting the clinical case definition (>= 102 deg fever + rash + either cough, coryza, or conjunctivitis) who either has a positive laboratory test for measles IgM antibody or is a contact of someone with a positive test.  Individuals meeting the clinical case definition who did not have laboratory confirmation and were not contacts were classified as “possible cases”.

The team members arrive in Rhode Island on March 1st.  They discover 13 individuals who met the clinical/laboratory case definition with dates of rash onset in February.  Ten of these 13 are Rhode Island residents, the other three are residents of neighboring states who were seen and treated at Brown University Medical Center in Providence, RI.  Nine of these 10 were still ill as of March 1.  The tenth, the probable index case for the outbreak, was a teenager who had traveled to Europe and returned three days prior to her rash onset.  She had recovered from her illness by the time the investigative team arrived.

During March, 31 additional Rhode Island residents were discovered who met the clinical case definition for measles, with rash onsets on or after March 1st.  Twenty-three of these had laboratory confirmation and 6 others were contacts of those who had.  An extensive statewide record-checking and vaccination program was undertaken throughout March, focusing on those schools, communities, and other settings where cases had occurred.  Only two of the cases had rash onset in the last week of March.

For the purposes of this exercise, use one million for the Rhode Island state resident population.

1)  What was the prevalence of measles in Rhode Island as of March 1st? 13

2)  What was the incidence of measles in Rhode Island for March?

3)  What would the incidence be if possible cases were included?

4)  If all but two of the February cases, and seven of the March (confirmed) cases had recovered by March 24, what would the prevalence have been as of that date?

Six thousand veterans of the armed services were recruited for a longitudinal, prospective cohort study of smoking-related cancers.  At the beginning of the study, a combination of interview and urinary cotinine tests ascertained that 1,450 of the veterans were current smokers.  An additional 1,935 veterans in the cohort had been regular smokers at some time in their lives but had quit (no cigarettes in the last 30 days) by the beginning date of the study.  None of the cohort members had any form of cancer as of the study start date.

During the five years of the study (for the purposes of this exercise we will make the very unrealistic assumption that none of the 6,000 veterans died nor were lost to follow up for the entire five years) lung cancer developed in 36 veterans who were current smokers, 18 who were former smokers, and 2 who had never smoked.  Bladder cancer developed in 10 current smokers, 11 former smokers, and 5 non-smokers.  All other forms of cancer combined developed in 41 current smokers, 24 former smokers, and 22 non-smokers.

5)  What was the incidence of lung cancer overall?

6)  What was the incidence of lung cancer in smokers, former smokers, and non-smokers?

7)  What was the incidence of bladder cancer overall?

8)  What was the incidence of bladder cancer in smokers, former smokers, and non-smokers?

9)  What was the incidence of all types of cancer combined, overall?

10)  What was the incidence of all types of cancer combined, in smokers, former smokers, and non-smokers?

11)  What was the relative risk of lung cancer in smokers compared to non-smokers?

12)  What was the relative risk of lung cancer in former smokers compared to non-smokers?

13)  What was the relative risk of bladder cancer in smokers compared to non-smokers?

14)  What was the relative risk of bladder cancer in former smokers compared to non-smokers?

15)  What was the odds ratio of all other forms of cancer in smokers compared to non-smokers?

16)  What was the odds ratio of all other forms of cancer in former smokers compared to non-smokers?

17)  What was the odds ratio of all types of cancer combined, in smokers compared to non-smokers?

18)  What was the odds ratio of all types of cancer combined, in former smokers compared to non-smokers?

19)  For #17 and #18 only, how closely does the odds ratio approximate the relative risk for smokers?  For former smokers?  Why?

20)  What was the attributable risk of lung cancer in smokers (compared to non-smokers)?

21)  What was the attributable risk fraction of lung cancer in smokers?

22)  What was the population attributable risk of lung cancer due to current smoking in this population (compared to non-smoking)?

23)  What was the population attributable risk fraction of lung cancer due to current smoking in this population (compared to non-smoking)?

24)  Why is the PAR fraction less than the AR fraction?  How do you think the PAR fraction would be  different if this study were done in the general population rather than in a population of veterans?

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