RE: st: RE: P-values for the difference in sensitivity in metandi

[Joe Canner <jcanner1@jhmi.edu>]

Carole,

I don't see anywhere in your data where you distinguish between physician-collected and patient-collected samples.  Is there a gold standard that you are comparing to?  Or is physician-collected the gold standard?

For the time being I am assuming the latter, in which case there is no p-value to calculate.  You are calculating a single sensitivity (0.825) and a single specificity (0.924), so there is nothing to compare.  Evaluating sensitivity and specificity is mostly a matter of clinical judgment, e.g., which is more problematic false negatives or false positives?  What is the prevalence of the disease in question?  This combination of sensitivity and specificity look pretty good, but depending on the clinical context they may be totally inadequate.

If you are talking about the former (comparing physician-collected and patient-collected with some gold standard), I'm not aware of such a thing (but don't take that to mean much; I didn't even know about -metandi- until you mentioned it and I could really have used it a few months ago).   However, a very legitimate (and to some, preferable) way to do that comparison is to see if the 95% confidence intervals overlap.  More to the point, however, is that the data you presented doesn't seem to represent a comparison between two methods versus a gold standard.

Regards,
Joe

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Carole Lunny
Sent: Tuesday, March 25, 2014 2:43 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: P-values for the difference in sensitivity in metandi

Dear Joe,

Thanks for replying. We are comparing the accuracy of self-collected
samples compared to clinician-collected samples.

Here is the data:

tp   fp tn fn
274 55 89 1510
238 101 74 2223
57 6 10 439
53 5 7 26
48 10 13 64
144 0 11 1039
6 3 1 42
53 9 9 85
75 10 9 41
31 2 4 11
50 22 19 285
9 7 4 73
28 4 8 63
85 32 9 121
67 24 17 114
31 7 10 51
49 5 2 258
17 3 0 25
30 0 12 12
62 13 0 71
407 59 23 1899
72 34 40 173
86 6 2 24
63 51 28 594
9 4 10 162
123 54 37 704
157 31 18 923
170 128 132 985