Table 3. Descriptive statistics of heatwave episodes occurrence for Boston MSA, 1991–2006: total duration and average timing; heat-related hospitalizations (HH); average daytime (Max T) and night time (Min T) temperature values during the heatwave episodes and relative risks with CI_95% of HH associated with heatwave episodes estimated from Model 3.

Heatwave sequence	Number seasons	Number of days	Mean (SD) Ordinal Day	Number of HH	HH per day	Max Temp °F Mean (SD)	Min Temp °F Mean (SD)	HW episode RR (CI95%)
1	1	27	196.7 (17.6)	124	4.59	87.4 (6.1)	68.8 (2.5)	15.3 (9.2–25.5)
2	4	39	213.7 (14.0)	42	1.08	87.3 (4.7)	69.1 (2.1)	3.8 (2.1–6.7)
3	4	33	214.3 (13.0)	30	0.91	87.2 (4.6)	68.9 (2.1)	2.7 (1.5–5)
4+	5	12	226.6 (17.2)	11	0.92	84.0 (5.3)	68.6 (2.3)	7.1 (2.7–18.9)