Models (b) and (c), with GLS setting, present slight differences. Of course, it seems better to use the temperature than to only use the threshold respect to a level. Yet the differences between these two models suggest that the evolution of temperatures when it is cold is crucial to explaining the influenza rate. Model (h) makes no improvement on the results of models (b) and (c) in terms of MSPE. In fact, it worsens them; this is probably due to collinearity among Tempn,s(t) and SRn,s(t). Concerning models (b), (c) and (d), the first two are preferable because they are easier to apply and interpret. Besides, in model (d) the measures of solar radiation usually depend on specialised devices, whereas the covariates related to temperature are readily available using standard (and cheaper) equipment. Finally, for short horizons, it seems unnecessary to specify high order autoregressive models, even though the improvement can be about 5% for larger lags.