English Social Sciences International Org/Dev/Coop

Countries without eligible death registration data
For these countries without death registration data at least 80% complete and with populations greater than 150 000, a regression model was used to estimate total road traffic deaths. As for the first report, we used a negative binomial regression model, appropriate for modeling non-negative integer count data (number of road traffic deaths) (Law 2009, Hilbe 2007). A likelihood ratio test was used to assess that the negative binomial model provided a better fit to the data than a Poisson model (where the variance of the data is constrained to equal the mean).
(equation)

where N is the total road traffic deaths (for a country-year), C is a constant term, Xi are a set of explanatory covariates, Pop is the population for the country-year, and  is the negative binomial error term. Population was used as **exposure**, making it possible to interpret the coefficients (βi) for the independent variables as effects on rates rather than a count. In a previous study, this type of model was used to represent "accident proneness" (Greenwood and Yule, 1920). Karlaftis and Tarko (1998) have also found a negative binomial regression model to be the appropriate for count data such as road traffic fatalities.

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