Table 1 Descriptive statistics and correlation analysis results

High-income

 Mean

292.950

32,756.230

4.658

102.506

 Max

6003.095

92,119.52

16.387

128.644

 Min

0.3

2762.764

0.3538

68.608

 Std. Dev

916.449

18,113.720

2.750

6.306

Correlation coefficients

 CO2

1

 GDP

0.464

1

 ENG

0.339

0.765

1

 EDU

0.004

− 0.113

− 0.121

1

Upper middle income

 Mean

355.666

5229.194

1.241

105.967

 Max

10,837.43

15,190.1

4.045

130.478

 Min

0.060

537.578

0.192

72.094

 Std. Dev

1349.520

2481.472

0.785

8.988

Correlation coefficients

 CO2

1

 GDP

0.135

1

 ENG

0.503

0.614

1

 EDU

− 0.085

0.036

− 0.127

1

Lower middle income

 Mean

57.894

1774.959

57.922

99.014

 Max

2227.675

4828.626

50,487.68

149.957

 Min

0.019

1.495

0.015

5.002

 Std. Dev

225.218

1015.760

1703.862

18.944

Correlation coefficients

 CO2

1

 GDP

0.061

1

ENG

0.367

0.380

1

EDU

0.021

0.416

0.055

1

Low-income

Mean

1.564

493.820

0.054

85.767

Maximum

11.496

913.092

0.260

156.404

Minimum

0.1

164.337

0.013

21.708

Std. Dev

1.659

183.782

0.043

35.913

Correlation coefficients

CO2

1

GDP

− 0.023

1

ENG

0.349

0.497

1

EDU

0.223

0.226

0.392

1