TABLE 1.

Time variables and strata for the case‐crossover structure

Time variables	Values	Strata
	Morning: 6 AM–10 AM	Month
	Midday: 10 AM–4 PM	Month × time of day
Time of day	Afternoon/evening: 4 PM–8 PM	Month × weekday
	Night: 8 PM–6 AM	Time of day × weekday
Month	1, 2, 3, …, 12
Weekday	0 if Saturday or sunday
	1 otherwise