Systematic review and meta-analysis of case-crossover and time-series studies of short term outdoor nitrogen dioxide exposure and ischemic heart disease morbidity

Table 3 Summary of subgroup analyses

Subgroup	Analysis	n	OR/RR	L95%CI	U95%CI	Q	p(Q)	I² (%)	p (difference)
Case-crossover
None	All single pollutant	34	1.074	1.052	1.097	212.91	< 0.01	91.1
Region	North America, Europe	21	1.048	1.029	1.066	68.19	< 0.01	68.4
Region	Other	13	1.104	1.061	1.149	112.20	< 0.01	91.4	0.019
Single/Multi pollutant	Single pollutant	9	1.075	1.019	1.135	95.89	< 0.01	98.2
Single/Multi pollutant	Multi-pollutant	9	1.038	0.995	1.083	41.65	< 0.01	96.2	0.23
Sex	female	8	1.050	1.004	1.098	27.93	< 0.01	64.8
Sex	male	8	1.032	1.006	1.058	14.66	0.04	52.0	0.51
Age	younger	8	1.023	0.997	1.05	14.25	0.05	43.3
Age	older	10	1.044	1.02	1.07	16.52	0.06	43.1	0.26
Time-series
None	All single pollutant	41	1.022	1.016	1.029	589.07	< 0.01	95.4
Region	North America, Europe	21	1.019	1.012	1.026	130.31	< 0.01	85.6
Region	Other	20	1.025	1.013	1.037	344.85	< 0.01	94.6	0.40
Single/Multi Pollutant	Single pollutant	8	1.013	1.003	1.023	86.79	< 0.01	94.3
Single/Multi Pollutant	Multi-pollutant	9	1.008	0.998	1.018	34.14	< 0.01	81.0	0.49
Age	younger	7	1.015	1.001	1.029	37.78	< 0.01	92.1
Age	older	8	1.033	1.011	1.056	65.01	< 0.01	95.2	0.18

ISSN: 1476-069X