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#1
10-21-2009
 Posts: 12 Threads: 3 Thanked 7 Times in 4 Posts
Sensitivity Specificity Equations

Sensitivity is also called the True Positive Rate
Specificity is also called the True Negative Rate
Sensitivity = TP rate
Specificity = TN rate

1 = TP rate + FN rate
therefore 1 - Sensitivity = FN rate
or Sensitivity = 1 - FN rate

1 = TN rate + FP rate
therefore 1 - Specificity = FP rate
or Specificity = 1 - FP rate

Increasing Prevalence increases positive predictive value and deceases the negative predictive value but it has nothing to do with sensitivity or specificity.

The Receiver operating Curve plots sensitivity(TP rate) in the Y axis and 1-Specificity (FP rate) in the X axis, area under the curve will be the accuracy of the test.
 The above post was thanked by: anoop_1198 (05-18-2010)

#2
10-21-2009
 USMLE Forums Scout Steps History: Not yet Posts: 56 Threads: 3 Thanked 25 Times in 18 Posts Reputation: 35

Are these high yield?

I think understanding the 2X2 box is all that's needed for both USMLE Step 1 and USMLE Step 2 CK
#3
10-23-2009
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 124 Threads: 27 Thanked 37 Times in 23 Posts Reputation: 57
what is the box

I have not done epidemiology yet and would like an explanation of what the box is

#4
10-23-2009
 USMLE Forums Veteran Steps History: --- Posts: 238 Threads: 56 Thanked 233 Times in 80 Posts Reputation: 263

The box is "Disease / No Disease" vs "Positive / Negative".

Basically, Disease + Positive = True Positive (usually the upper left box), whereas No Disease + Negative = True Negative (usually lower right box).

The box is high-yield.
 The above post was thanked by: anoop_1198 (05-18-2010)
#5
12-26-2009
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 741 Threads: 137 Thanked 2,573 Times in 446 Posts Reputation: 2676
2X2 Table

See this thread also
http://www.usmle-forums.com/usmle-st...tt-square.html
 The above post was thanked by: anoop_1198 (05-18-2010)

 Tags Biostatistics-Epidemiology

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