Table 1.

Source of detection of marijuana use

Source	Number	Percent of all women (%)	Percent of all positives (%)
None	244	67	—
Any positive	119	33	100
Questionnaire only	6	2	5
Obstetrical record only	8	2	7
Urine only	46	13	39
Questionnaire and urine	12	3	10
Questionnaire and record	4	1	3
Record and urine	27	7	23
All three	16	4	13

Sensitivity of questionnaire = (6 + 12 + 4 + 16)/119 = 32%.

Sensitivity of obstetrical record = (8 + 4 + 27 + 16)/119 = 46%.

Sensitivity of urine = (46 + 12 + 27 + 16)/119 = 85%.