Middle and low and low income Student

−0.154^*** (−3.438)

−0.024 (−1.115)

−0.115^*** (−2.94)

0.012 (0.452)

GDP

1.493^*** (13.401)

1.761^*** (30.159)

0.945^*** (7.336)

0.445^*** (3.277)

IGDP

0.976^*** (6.384)

0.906^*** (6.978)

0.926^*** (7.104)

0.381^*** (2.610)

population

−0.467^*** (−4.682)

−0.420 (−1.024)

−0.020 (−0.186)

−0.200 (−0.420)