This site is intended for healthcare professionals
Login | Register (NOW FREE)

Medical search

sensitivity and specificity

FREE subscriptions for doctors and students... click here
You have 3 open access pages.

These are statistical terms that are often confused. These terms can be illustrated by way of an example:

At a particular hospital a MIBG scanner is used to detect phaeochromocytomas. A positive scan was reported in 38 cases. An audit showed:

  • true positive (TP) 10, true negative (TN) 25,
  • false positive (FP) 0, false negative (FN) 3

where:

  • patients with phaeochromocytoma TP (person with a phaeochromocytoma and positive test)
  • patients with phaeochromocytoma FN (person with a phaeochromocytoma and negative test)
  • patients without phaeochromocytoma FP (person without a phaeochromocytoma with a positive test)
  • patients without a phaeochromocytoma TN (person without a phaeochromoytoma with a negative test)

phaeochromocytoma present phaeochromyctoma absent

test result positive

TP = 10

test result positive

FP = 0

test result negative

FN = 3

test result negative

TN = 25

  • sensitivity = 100xTP /(TP+FN) = 100 x 10(10 + 3) = 77%
    • i.e. proportion of people with a phaeochromocytoma who are corectly identified by the screening test = 77%

  • specificity = 100xTN /(TN+FP) = 100 x 25 /(25+0) = 100%
    • i.e. proportion of people without phaeochromocytoma who have had a negative test result = 100%

  • positive predictive value = 100xTP/(TP+FP) = 100 x 10/(10+0) = 100%

i.e. the proportion of screening tests that are correct.

Links:

The information provided herein should not be used for diagnosis or treatment of any medical condition. A licensed medical practitioner should be consulted for diagnosis and treatment of any and all medical conditions. Copyright 2016 Oxbridge Solutions LtdĀ®. Any distribution or duplication of the information contained herein is strictly prohibited. Oxbridge Solutions LtdĀ® receives funding from advertising but maintains editorial independence. GPnotebook stores small data files on your computer called cookies so that we can recognise you and provide you with the best service. If you do not want to receive cookies please do not use GPnotebook.