Table 1.

Estimation results of negative binomial regression.

Variables	Estimate	Std err of $\hat{\beta }$	Conf. Int. of $\hat{\beta }$	IRR
Intercept	−5.203∗∗∗	0.763	(-6.649, −3.699)	0.005
Air transfer	1.151∗∗∗	0.138	(0.901, 1.394)	3.161
Airport number	0.982∗∗∗	0.204	(0.549, 1.401)	2.670
Schengen	1.503∗∗∗	0.431	(0.622, 2.383)	4.498
Population density	0.876∗∗∗	0.216	(0.308, 1.422)	2.403
Old	0.066∗∗	0.025	(0.017, 0.119)	1.068
Dispersion parameter	0.567	0.058
Pseudo-R2	0.76
Log.Lik.	−1049.602
AIC	2113.20

^a Schengen = 0 is taken as reference category; IRRs, incident rate ratios; AIC, Akaike information criteria.

∗P < 0.1, ∗∗P < 0.05, ∗∗∗P < 0.01.