Table 1.

Timing of cannabis onset relative to hazard and control intervals: Data from the NSDUH, 2001–2006

	Cannabis onset during the control interval (the month before cocaine onset)		Total
Cannabis onset during the one month hazard interval of first cocaine use	Yes	No	Row Total
Yes	Undefined*	n=48	48
No	n=30	n=3,412	3,442

Estimated Relative Risk = 1.6; Exact mid-p-value = 0.042.

Notes: This table should be read as one reads a corresponding table from research on discordant MZ co-twin pairs. That is, informative cases are those with cannabis onset in the hazard interval but not in the one-month control interval (upper right-hand cell, n = 30). The relative risk estimate from this table is 48 / 1 / 30 / 1. As in discordant MZ co-twin estimates, values in the upper left-hand cell and lower right-hand cell do not contribute information to point estimate calculations. Each hazard interval is the calendar month in which cocaine onset occurred. The control interval is specified to be the one month immediately prior to the hazard interval.