Table 2.

Daily exposures among the PTB cases, Detroit, Michigan area, May to September, 1991 to 2001

	N	Median	Mean	Min	Max
Two-day mean apparent temperature, °C	9053	18.6	18.0	3.1	28.0
Two-day mean apparent temperature 18.6°C and above	9053	0.1	1.5	0.0	9.4
Mean solar radiation (W/m2)	9053	226.4	217.7	38.1	352.8
Total precipitation (mm)*	9053	0.0	0.4	0.0	56.7
Mean wind speed (m/s)	9053	3.6	3.6	0.1	8.0
Maximum 8 hour average ozone (ppb)	9039	43.0	44.8	3.2	102.0
Mean particulate matter, 10 µm or less (μg/m3)*	8331	39.0	38.5	8.0	158.0
Mean nitrogen dioxide (ppb)*	8956	18.4	19.7	0.0	72.8

*Geometric means are provisded. Values were natural-log-transformed in the regression analyses.

PTB, preterm birth.