Int. J. Environ. Res. Public Health 2011, 8 922 without interaction terms are estimated. Using a Bayesian model selection criterion (Akaike Information Criteria (AIC)) as in Woods [43], we find that nonparametric model specifications with or without temperature and precipitation interaction term perform the best and all the linear specifications perform poorly. However, the temperature and precipitation interaction term is statistically insignificant (in fact the interaction effects are already captured through the monthly standard deviation of precipitations variable).We retained the nonparametric model specification without temperature and precipitation interaction term. Figure 3. Effect of precipitation levels on per capita malaria cases conditional on climate variability with 95% confidence intervals. This graph is the plot of the precipitation function in Equation (8). It shows how temperature levels affect malaria prevalence given the current climate variability conditions measured as the standard deviation in precipitation. The varying-coefficients obtained for temperature and precipitation are used to calculate the elasticity of the number of malaria cases with respect to climate factors for each of the 25 countries. Since the dependent variable is the log of malaria cases, the equation estimated is . The change in percentage of the number of malaria cases with respect to a one percent change in temperature or precipitation hereafter called elasticity is calculated as and averaged over the 11 years period of study for each country. The results in Table 3 (columns 3 and 4) suggest that the number of malaria cases in most of the countries is very responsive to changes in temperature excepting the findings in Botswana, Chad, South Africa and Tanzania where the response is small. Negative temperature effects are only observed in Central African Republic, Ethiopia and Guinea. The number of malaria cases is also very responsive to precipitation levels in Algeria, Central African Republic, Cote d’Ivoire, Djibouti, Egypt, Ethiopia, Ghana, Guinea, Malawi, Morocco, Rwanda, and Sudan but less responsive in Benin, Botswana, Burkina, Chad, Mauritania, Mali, Niger, South Africa, Togo, Uganda, Tanzania and Zimbabwe.