**4.3 Evaluation of the covariance structure of georeferenced data**

After selecting the spatial model and the variables, we proceeded to estimate the covariance structure of the Gaussian process. For this, the Exponential, Gaussian, and Matérn covariance functions were tested, taking CDCs as the response variable, and measures of central tendency of the explanatory variables maximum environmental temperature, altitude, patient age, and average monthly rainfall were taken. Of the three functions, the Matérn covariance function generated the best value for *ME* ¼ �1*:*185 and *MSNE* ¼ 0*:*885, that is, *ME* tends to 0 and *MSNE* tends to 1, therefore a covariance function Matérn can be assumed for the fitted spatial model.
