Does Airport Preferential Policy Aggravate the Competition of Aviation Hubs in Central and Western China? Based on the Investigation of 78 Airports

Table 2

Descriptive statistics of main indicators.

Variables	N	Mean	SD	Min	Max
lntra	1,404	13.900	2.314	2.773	18.580
lncm	1,404	8.844	2.984	0.095	15.260
sec	1,404	45.310	10.870	14.950	82.280
lnrf	1,404	9.716	1.915	1.792	13.560
lngdp	1,404	16.510	1.219	12.670	19.600
lnpop	1,404	6.066	0.690	3.884	7.297
pd	1,404	0.049	0.037	0.002	0.271
esis	1,404	0.078	0.088	0.008	0.958
lntea	1,404	8.493	1.385	2.773	11.160
proad	1,404	5.826	6.403	0.049	64.000
lnta	1,404	0.903	0.742	0.044	4.633
gov	1,404	1.974	1.144	0.649	12.400