Association of invasive meningococcal disease and environmental and virologic
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Weekly counts of invasive meningococcal disease (IMD) reported cases from country A
in 1997-2000 were collected and analyzed, to study associations between IMD and
environmental and virologic exposure. The file ‘imd.csv’ stored the following variables
which were found to be significant factors from the literature in other places:
flu: influenza isolation rate from laboratory
maxtemp: weekly maximum temperature
IMD: weekly number of IMD cases
pop: population size
a) Fit a poisson regression model to predict weekly IMD cases using flu and maxtemp,
accounting for the increasing population size in 1997-2000. Summarize your results
in a table.
b) Assess the goodness of fit of the model.
c) Quote the mean and variance of the weekly IMD cases. Is there any evidence of
overdispersion?
d) Fit a negative binomial regression model to predict weekly IMD cases and summarize
your results in a table.
e) Assess the goodness of fit of the model.
f) Calculate the AIC for the poisson and negative binomial regression models and select
the best model based on AIC and goodness of fit.
g) Assess if the linear effects for the variables flu and maxtemp are adequate.
h) Assess if there is any collinearity problem in your final model?
i) Assess if there is any unexplained serial correlation after fitting your final model.
j) Draw an overall conclusion on the findings.
k) Based on the final model, predict the number of IMD cases in a week, if the influenza
isolation rate is 0.3, with a maximum temperature of 5ºC and a population of 110
l) Based on the final model, which of the conditions below will have a higher
population risk of IMD, so more attention should be paid to suspected IMD cases for
earlier treatment?
1. Influenza isolation rate = 0.1, maximum temperature = 10ºC
2. Influenza isolation rate = 0.4, maximum temperature = -5ºC
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