International Scholarly Research Notices

Research Article

A Combined Model of Global Cultivated Area Change and Prediction for Future: 1961–2020

Table 5

ADF and PP tests for global cultivated change time series**.
Test typeVariable Trend form (C, T)* value1%5%10%Judgment
ADFStandard valueWith C, without T −2.32−4.17−3.51−3.19Non-stationary
First differenceWithout C, without T −4.45−2.62−1.95−1.61Stationary
PPStandard valueWith C, with T −1.92−4.17−3.51−3.18Non-stationary
First differenceWithout C, without T −4.49−2.62−1.95−1.61Stationary
Note: *C means intercept term, and T means trend term with time. **ADF and PP test equations often have three forms: with intercept term but without trend term, with intercept term and with trend term, without intercept term and without trend term. Global cultivated area time series has trend and intercept terms, but the first difference series has no trend and intercept terms.