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Category | Math |
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Subject | Statistics |
Difficulty | Graduate |
Status | Solved |
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Assignment Description
CMED 6210 Infectious Disease Epidemiology
HW5
Question 1 (60 points)
A novel pandemic influenza virus has just started to spread in the population. No individuals have antibodies against the new virus at the start of this epidemic. A serial cross-sectional serologic surveillance system has been set up to estimate the number of infections at 30 and 60 days after the epidemic has started. Reliable research studies show that 90% of individuals infected by this new pandemic virus become seropositive. Ignore the delay between infection and seropositivity. The seroprevalence data are as follows:
Day | Number of subjects tested | Number of subjects seropositive |
30 | 195 | 30 |
60 | 175 | 86 |
a) Read the documentation of Binomial Distribution in R. Use the binomial distribution to provide a maximum likelihood estimate and the associated confidence intervals for seroprevalence on days 30 and 60 (20 points).
b) Use your answer in question 1(a) to estimate the (cumulative) infection attack rate on days 30 and 60 (20 points).
c) Estimate the infection attack rate between days 30 and 60 (20 points).
Question 2 (40 points)
Read Riccardo et al Eurosurveillance 2011 and download the spreadsheet for this question.
a) Modify the algorithm in Riccardo et al by using 4-weekly moving averages and 95% confidence intervals as the threshold for triggering alerts. Describe and explain how this modified algorithm triggers syndromic surveillance alerts (10 points).
b) The spreadsheet contains weekly influenza-like-illness (ILI) surveillance data for a hypothetical population. Use the algorithm in question 2(a) to calculate the expected incidence and 95% confidence interval of the observed incidence and enter these numbers into columns 3-5 of the spreadsheet, and submit the spreadsheet (in Excel) as well (10 points).
c) Plot the expected incidence, the observed incidence and the 95% confidence intervals of the observed incidence over time in the same figure (10 points).
d) In which weeks would an ‘alert’ be issued based on this syndromic surveillance algorithm (10 points)?