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#1
07-17-2010
 USMLE Forums Guru Steps History: Not yet Posts: 414 Threads: 30 Thanked 87 Times in 70 Posts Reputation: 97
Screening Test Accuracy on this graph?

The attached graph shows three different cut off points for a screening test.

I can't seem to understand why C is the best accuracy point? Shouldn't it be D!

click to enlarge
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#2
07-17-2010
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its explained well in the Kaplan lecture notes dear friend... turn a few pages back from the page u v attached
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#3
07-17-2010
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i know its in kaplan

Quote:
 Originally Posted by doctorF its explained well in the Kaplan lecture notes dear friend... turn a few pages back from the page u v attached
I read it back and forth I cant get it, there is just a formula there not the relation with graph, even the lecture, it is just mentioned in there and not explained.
I don't understand why it is not D?????????????????????.

If its so easy for you can you please explain it.:sorry:

and why is it C???
where you have equal number of both patients?

may be its too easy for you. not for me.

I don't
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#4
07-17-2010
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Quote:
 Originally Posted by Kabutar111 I read it back and forth I cant get it, there is just a formula there not the relation with graph, even the lecture, it is just mentioned in there and not explained. I don't understand why it is not D?????????????????????. If its so easy for you can you please explain it.:sorry: and why is it C??? where you have equal number of both patients? may be its too easy for you. not for me. I don't

Simply the reasson is this ... As you see the normal cut off point between the dis & non-dis people is "C". So, if we simply move the cut off point to any zone forward (towards D) or backwards (towards B), it may cause the results "overall regarding the sensitivity & specificity both" to be less accurate.
Indeed, for this reason too, the point "C" is the area where you can say this test has "high" specificity & sensitivity both. And if we move to D or B, the result will cause increase & decrease in specificity or sensitivity at the same time. At this point "high sensitivity & low specificity" or vice versa.
I hope I made things clear
#5
07-17-2010
 USMLE Forums Guru Steps History: Not yet Posts: 414 Threads: 30 Thanked 87 Times in 70 Posts Reputation: 97

Quote:
 Originally Posted by Mohabravo Simply the reasson is this ... As you see the normal cut off point between the dis & non-dis people is "C". So, if we simply move the cut off point to any zone forward (towards D) or backwards (towards B), it may cause the results "overall regarding the sensitivity & specificity both" to be less accurate. Indeed, for this reason too, the point "C" is the area where you can say this test has "high" specificity & sensitivity both. And if we move to D or B, the result will cause increase & decrease in specificity or sensitivity at the same time. At this point "high sensitivity & low specificity" or vice versa. I hope I made things clear
you did thanks,
i dint know we have t consider both sensi and specifici to decide the point of accuracy.
i thought more probability of getting right test and more accurate screening.
although i have remember it know.
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#6
07-18-2010
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yep good explanation.

just remember than with accuracy the test has to be trustworthy, n for that it should have the least bias. n a center point C is the least biased result.

 Tags Biostatistics-Epidemiology

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