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Diagnostic Test Accuracy

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by

Ahmed Negida

on 4 February 2015

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Transcript of Diagnostic Test Accuracy

Diagnostic Test Accuracy
A psychiatrist devised a short screening test for depression. An independent blind comparison was made with a gold standard for diagnosis of depression among 200 psychiatric outpatients. Among the 50 outpatients found to be depressed according to the gold standard, 35 patients were positive for the test. Among 150 patients found not to be depressed according to the gold standard, 30 patients were found to be positive for the test.

a- The prevalence of depression was 80%
b- The positive predictive value was 80%
c- The negative predictive value was 80%
d- The specificity was 80%
e- The sensitivity was 80%
1- FALSE POSITIVE (n=10)
2- FALSE NEGATIVE (n=5)
3- TRUE POSITIVE (n=150)
4- TRUE NEGATIVE (n=35)
Positive and negative predictive values
PPV = True positive/ (True + False)Positive
NPV = True Negative/ (True+False) Negative

How to calculate the prevalence of the disease from Diagnostic test parameters ?

Predictive values only change with prevalence of the disease, why ?
Sensitivity
How many real cases was diagnosed with the disease from the total number of cases that already have the disease.

Sensitivity = (True Positive/ Total True)%

Importance !
Reliability Vs Accuracy
- Theoretically a test with (100% sensitivity) is ideal.

- Reality:
No test is accurate 100%

- There is always a percent of error !
So ..
Let's Imagine
Specificity
How many cases wasn't diagnosed by the disease from the total disease free population ?

Specificity = (True -ve / Total Negative)%

Importance !
By:
Ahmed Said Negida

- 3rd year medical student at Zagazig university
- Global Surgery National Coordinator
- Member at AAN