Research on Influencing Factors of Effective Gas Extraction Radius in Coal Mine Based on Multiple Linear Regression

Table 3

Level values of each factor.

Level	Hole diameter (mm)	Extraction negative pressure (MPa)	Initial permeability of coal seam (×10^−17m^2)	Extraction time (d)
1	75	8	2.4	20
2	94	13	4.4	60
3	113	18	6.4	100
4	130	23	8.4	140