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Old 07-07-2012
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Stats Sensitivity, Specificity, PPV, NPV

What's the relationship between specificity+sensitivity on one side, and NNV+PPV on the other side?

For example:
When you decrease PPD, what happens to the sensitivity and specificity?
When you decrease the NPD, what happens to the sensitivity and specificity?

The reason I'm asking is a few UW questions that have been bugging me.
Plus there's this diagram in FA that i always end up staring at for an hour or so, it's on the page of sensitivity, specificity, PPV, NPV.
What happens if you move the B line to the right? and what happens if you move the B line to the left?

P.S. I know i asked alot of questions but they can all be traced back to one concept
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Old 07-07-2012
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I just found this

What is the effect of the cut-off value on sensitivity/specificity/predictive values?

I think they're talking about the same thing, i'm just not able to fully digest this concept i dont know why!
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Old 07-07-2012
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i think i got it

B line to the right (increasing your cut-off point) means:
higher specificity and lower sensitivity
with a higher PPV (because of lower false-positives).
-So a good specificity means a higher PPV due to lower false-positives

B line to the left (decreasing your cut-off point):
lower specificity and higher sensitivity
with a higher NPV (because of lower false-negatives)
-So a good sensitivity means a higher NPV due to lower false-negatives

FA should have labeled the diagram with the TN's, TP's, FP's, and FN's. After knowing which part of the diagram is which, it all becomes very easy.

Concept down!
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Old 07-07-2012
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Quote:
Originally Posted by Renaissance View Post
What's the relationship between specificity+sensitivity on one side, and NNV+PPV on the other side?

For example:
When you decrease PPD, what happens to the sensitivity and specificity?
When you decrease the NPD, what happens to the sensitivity and specificity?

The reason I'm asking is a few UW questions that have been bugging me.
Plus there's this diagram in FA that i always end up staring at for an hour or so, it's on the page of sensitivity, specificity, PPV, NPV.
What happens if you move the B line to the right? and what happens if you move the B line to the left?

P.S. I know i asked alot of questions but they can all be traced back to one concept

Lol, are you talking about that bimodal or bi-hump or something curve? I hate it too. It seems simple when i look at it but then it gets soo confusing when trying to solve a question ughhhhhhhhhhh i still dont understand why we as doctors need to know that hump.
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I've become so numb
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