Table 4.

Summary of population bias

Outcome	Pollutant	Beggs’ test		Egger’s test
		Z	P	t	P
LBW	NO2	1.25	0.213	0.43	0.677
	PM10	0.93	0.350	–1.84	0.100
	SO2	1.22	0.221	2.85	0.065
	CO	0.34	0.734	–0.04	0.968
	O3	1.70	0.089	5.03	0.037
PTB	NO2	1.11	0.266	0.03	0.979
	PM10	–0.12	1.000	0.22	0.831
	CO	0.30	0.764	0.82	0.448
	NOx	–0.24	1.000	–2.98	0.059
	PM2.5	2.26	0.024	–2.64	0.023
SGA	NO2	0.24	0.806	0.86	0.451
	PM10	1.70	0.089	–3.62	0.069
	PM2.5	–0.24	1.000	–0.21	0.847