SCREENING TEST

  Gold Standard
  Dis (+) Dis (-)
Test (+) a b
Test (-) c d

  Percent
Sensitivity TP/(TP+FN) a/(a+c)
Specificity TN/(FP+TN) d/(b+d)
PPV TP/(TP+FP) a/(a+b)
NPV TN/(FN+TN) d/(c+d)

True Positive (a) = Test (+) Disease (+)
False Positive (b) = Test (+) Disease (-)
False Negaive (c) = Test (-) Disease (+)
True Negative (d) = Test (-) Disease (-)

Accuracy = (True Positive + True Negative) / (Total)
Precision = (True Positive) / (True Positive + False Positive)

[http://gotoknow.org/blog/epistat/393264]

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