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#1
10-31-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 584 Times in 354 Posts Reputation: 594
Positive Predictive Value from Specificity and Sensitivity!

Several tests have been developed to measure serologic markers of breast cancer. The sensitivity and specificity for
diagnosis of early stage breast cancer vary from test to test. If positive, which of the following tests will have the
highest predictive value for the disease?
o A) Sensitivity - 80%, specificity- 90%
0 B) Sensitivity - 65%, specificity - 97%
o C) Sensitivity - 70%, specificity - 94%
0 D) Sensitivity - 75%, specificity - 92%
0 E) Sensitivity - 85%, specificity - 90%

#2
11-01-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 385 Threads: 6 Thanked 205 Times in 154 Posts Reputation: 215

Specificity = probability that a person without the disease will test negative. In other words, the more specific the test, the more chances are that the person has the disease. So answer should be B.
 The above post was thanked by: tyagee (11-01-2012)
#3
11-01-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 720 Threads: 217 Thanked 551 Times in 308 Posts Reputation: 561

N for N --- seNsitivity related to Negative predictive value..

P for P ---- sPecificity related to Positive predictive value

 The above post was thanked by: Novobiocin (11-01-2012)
#4
11-01-2012
 USMLE Forums Scout Steps History: Not yet Posts: 75 Threads: 3 Thanked 35 Times in 23 Posts Reputation: 45

So if u r trying to catch breast cancer earlier, you will need a test that will be make u confident enough that the lady who tests positive indeed has the test. So option B is the most likely one
 The above post was thanked by: tyagee (11-01-2012)
#5
11-01-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 584 Times in 354 Posts Reputation: 594

Quote:
 Originally Posted by cingulate.gyrus N for N --- seNsitivity related to Negative predictive value.. P for P ---- sPecificity related to Positive predictive value
hey cingulate, this vertical line to left in graph.... doesnt it denotes Sn ?
#6
11-01-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,216 Threads: 41 Thanked 1,316 Times in 706 Posts Reputation: 1331

B, the greatest value of specificity is the one you are looking for

Specificity rules IN

Sensitivity rules OUT

IN order to rule in you have to have an excellent PPV.
In order to rule out you have to have an excellent NPV

So that if a specific test comes back positive then you have the disease no matter what.
 The above post was thanked by: Novobiocin (11-01-2012)
#7
11-01-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 720 Threads: 217 Thanked 551 Times in 308 Posts Reputation: 561

Quote:
 Originally Posted by tyagee hey cingulate, this vertical line to left in graph.... doesnt it denotes Sn ?

The right of vertical line is sensitivity( All the diseased case).
And the left of which is negative predictive value(Non of the diseased case)

similarly a life can be drawn in other side which divide graph to specificity and positive predictive value..

Its beautifully described in Kaplan vedios... watch it...Difficult to expain.
 The above post was thanked by: Novobiocin (11-01-2012), tyagee (11-02-2012)
#8
11-01-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,085 Times in 1,046 Posts Reputation: 2105

Quote:
 Originally Posted by cingulate.gyrus Its beautifully described in Kaplan videos...
Especially the part where Dr.Daugherty said only to look at the bottom of the graph and ignore the top.
__________________
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 The above post was thanked by: tyagee (11-02-2012)

 Tags Biostatistics-Epidemiology, Step-2-Questions

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