The test characteristics of a biased or ignorant diagnostician

Table 1 Examples of the joint influence of two sequential tests

Scenario	2nd Test matrix		1st Test matrix		Combined test matrix
Scenario	Dx + (%)	Dx− (%)	Dx + (%)	Dx− (%)	Dx + (%)	Dx− (%)
Perfect 2nd tester
T+	100	0	80	10	80	10
T−	0	100	20	90	20	90
Perfect 1st tester
T+	80	10	100	0	80	10
T−	20	90	0	100	20	90
Imperfect 2 testers
T+	80	10	70	15	59	20
T−	20	90	30	85	41	80
Ignorant 2nd tester
T+	50	50	70	15	50	50
T−	50	50	30	85	50	50
Ignorant 2nd tester
T+	50	50	100	0	50	50
T−	50	50	0	100	50	50

T+ and T− represent a positive or negative test result, respectively. Dx+and Dx− represent a positive or negative diagnosis, respectively

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