*3.1. Cultivation Area*

The potato cultivation area in 2000–2019 indicated a systematic decline in this value starting from 2002. In 2019, the potato cultivation acreage was only 26.2 thousand hectares, whereas 20 years earlier, there were three times more. The results of the regression analysis showed a downward trend according to the second-degree parabolic regression (Figure 1). The relationship between the analyzed features is usually characterized by the correlation coefficient R, assuming values in the range [−1.1]. It determines the strength of the relationship between the variables. However, the measure of the fit of the regression line to empirical data is the coefficient of determination R2, taking values in the range [0.1] or [0%, 100%]. Moreover, the coefficient of determination can be corrected by the number of degrees of freedom, which increases its value.

**Figure 1.** The actual general area of potato cultivation and the tendency of changes in this area in the southeastern part of Poland, 2000–2019.
