Table 1.

Results of quality assessment.

	Data points	High risk	Proportion high risk
Recruitment bias	204	28	14%
Non‐response	204	121	59%
Ascertainment of illicit drug use	204	43	21%
Ascertainment of health‐care utilization	204	44	22%
Adequacy of follow‐up	82	21	26%
Selection of comparison group	47	4	9%
Adjustment for confounders	47	4	9%
Global assessment	204	58	28%