Table 1 Phillips–Perron unit root test.

From: Waste-to-energy and its asymmetric impact on ecological footprint: implications for environmental sustainability

China

Level

First difference

 

Constant

Trend

Constant

Trend

EFP

−0.6256

−1.5579

−3.8850***

−3.9159***

WTE

−0.2999

−1.8973

−4.2262***

−4.1340***

GDP

−1.9168

0.5447

−3.4521***

−3.9012***

FD

−3.6894**

−1.5717

−5.6614***

−7.7560***

FDI

−5.5449***

−3.6618

−5.7533***

−7.1071***

United States

Level

First difference

 

Constant

Trend

Constant

Trend

EFP

−1.7372

−1.0833

−6.3643***

−7.6750***

WTE

0.9964

−2.0054

−8.4186***

−10.4341***

GDP

−2.1849

−0.8656

−5.1871***

−5.4162***

FD

−1.2269

−1.2724

−4.9998***

−5.1286***

FDI

−2.0201

−3.5018

−8.8988***

−9.5696***

  1. *** and ** represent significance at the 1% and 5% significance levels, respectively.
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