Table 3.

Detection rate (%), false positive rate (%) and ratio of true to false positive for predictive probability using various risk thresholds

	Predictive probability of increased violence for cut-off of a positive test result
Nurses	5%	10%	15%	20%	25%	30%	35%
Detection rate	83.9	34.4	15.1	6.5	2.2	2.2	1.1
False positive rate	55.0	21.8	8.4	2.7	0.87	0.10	0.10
Ratio true to false positive	1/7	1/7	1/6	1/5	1/5	½	1/1
Practical nurses
Detection rate	94.8	85.2	61.7	35.7	18.3	8.7	6.1
False positive rate	82.5	63.5	37.0	19.9	9.7	5.9	3.8
Ratio true to false positive	1/5	1/4	1/4	1/3	1/3	1/4	¼
Social and youth workers
Detection rate	70.0	40.0	26.7	20.0	20.0	3.3	3.3
False positive rate	29.6	12.8	6.3	3.5	2.5	0.96	0.36
Ratio true to false positive	1/12	1/12	1/9	1/7	1/5	1/4	1/3
Teachers
Detection rate	64.4	2.7	1.4	–	–	–	–
False positive rate	44.1	3.8	0.89	–	–	–	–
Ratio true to false positive	1/17	1/35	1/16	–	–	–	–