3. Results and Discussion
3.1. Description of the data
Figure 3 (a and b) shows the time series of the variables from 1980 through 2011. Population displays an exponential increase. It is clear that all types of crop production rapidly increased. All four time series show almost the same pattern and follow the precipitation pattern. Almost all the lower values of the three crops’ lines correspond to the lower values of precipitation, and almost all the higher values for those crop production correspond to the higher values of precipitation. For the regression analysis, the predictive or independent variables are population and precipitation, whereas the dependent or predicted variables are crops, namely sorghum, maize, and rice.