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S05 Screening & Diagnostic Tests (FILLED IN)

# Net sensiuvity series tesung ve ve ve ve 225

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Unformatted text preview: true prevalence): ﬁrst using skin test, then chest x- ray –  Test #1 à༎Skin test: Sn = 75%, Sp = 80% –  Test #2 à༎Chest x- ray: Sn = 90%, Sp = 80% •  Step 1: Determine the 2x2 table for our 1st test Example (Series TesUng) - ve +ve - ve +ve 225 940 1,165 +ve 203 188 391 - ve 75 3,760 3,835 - ve 22 752 774 300 4,700 5,000 225 940 1,165 Test #2 True Disease Status +ve Test #1 True Disease Status •  Step 1: Determine the 2x2 table for our 1st test –  Skin test: Sn = 75%, Sp = 80% •  Step 2: Determine the 2x2 table for our 2nd test –  Chest x- ray: Sn = 90%, Sp = 80% Ex. “Net SensiUvity” (Series TesUng) - ve +ve - ve +ve 225 940 1,165 +ve 203 188 391 - ve 75 3,760 3,835 - ve 22 752 774 300 4,700 5,000 225 940 1,165 Test #2 True Disease Status +ve Test #1 True Disease Status •  Net SensiUvity à༎ –  How many were correctly diagnosed +ve who were diseased? –  203 of the 300 correctly diagnosed: 203 / 300 = 67.7% –  Does this diﬀer from the individual test Sn’s? LOWER Ex. “Net SensiUvity” (Series TesUng) - ve +ve - ve +ve 225 940 1,165 +ve 203 188 391 - ve 75 3,760 3,835 - ve 22 752 774 300 4,700 5,000 225 940 1,165 Test #2 True Disease Status +ve Test #1 True Disease Status •  Net Speciﬁcity à༎ –  How many were correctly diagnosed - ve who were disease free/nega2ve? –  Of 4,700… 3,760 in the ﬁrst test PLUS 752 in the second test –  (3,760 + 752) / 4,700 = 96% –  Does this diﬀer from the individual test Sp’s? HIGHER Example (Parallel TesUng) Sn = 90% Sp = 75% - ve +ve 140 360 500 - ve 60 1440 1500 200 Test #1 +ve 1800 2000 Test #2 Sn = 70% Sp = 80% True Disease Status True Disease Status +ve - ve +ve 180 450 630 - ve 20 1350 1370 200 1800 2000 •  Outbreak of meningi2s among 2000 high school students (10% true prevalence) two tests simultaneously –  Test #1 à༎ Medical exam: Sn = 70%, Sp = 80% –  Test #2 à༎Lumbar punch test: Sn = 90%, Sp =...
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