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Information Mastery 2

Information Mastery 2. Diagnostic tests. Technical vs. Clinical Precision. Sensitivity % of patients with the disease who have a positive test Number with positive test/Number with disease Specificity % of patients without the disease who have a negative test

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Information Mastery 2

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  1. Information Mastery 2 Diagnostic tests

  2. Technical vs. Clinical Precision • Sensitivity • % of patients with the disease who have a positive test • Number with positive test/Number with disease • Specificity • % of patients without the disease who have a negative test • Number with negative test/Number without disease • Positive Predictive Value • % of patients with a positive test who have the disease • Number with disease/ Number with positive test • Negative Predictive Value • % of patients with a negative test who don’t have the disease • Number without disease/ Number with negative test

  3. Specificity Large holes catch most of the big fish but let through the small fish. (Most of the fish will be the big fish you want – SpPin)

  4. Sensitivity Small holes catch all the big fish and many small fish. (If there are no big fish in the net, they probably aren’t out there – SnNout)

  5. Technical Precision • Specificity: Remember SpPIn When a test has a high Specificity, a Positive test rules IN the disorder. • Sensitivity: Remember SnNOut When a test has a high Sensitivity, a Negative result rules OUT the disorder. But watch out for the prevalence of the disease or this can mislead you

  6. Summary • Sensitivity • How good the test is at picking up disease (SnNOut) • Specificity • How good the test is at identifying people who do not have the disease (SpPIn) • Positive Predictive Value (PPV) • Chance that someone testing positive truly has the disease • Negative Predictive Value (NPV) • Chance that someone testing negative does not have the disease • As prevalence decreases, PPV decreases and NPV increases

  7. So what does all this mean? • In primary care many people have a low chance of having the disease they are being tested for. • If they get a positive test then they may have the disease – or it could be a false positive. They may need more tests to sort out whether they truly, truly have the disease. • (But what will the patient think when you tell them their initial test indicates they may have something and they need further tests?) • If they get a negative test, and they are unlikely to have the disease, then it’s really very unlikely that they have it when they have tested negative. • And MOST IMPORTANTLY, try only to test people for anything if they are in a high risk group for having the disease. Testing lots of people will do more harm than good.

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