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srikanthguduru / imrmc

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Negative variance estimation result. #26

Open GoogleCodeExporter opened 9 years ago

GoogleCodeExporter commented 9 years ago 
I get negative variance values for some files with the error message attached.
Even if I proceed with MLE estimates, I don't get variance results. What should 
I do?

Original issue reported on code.google.com by silv...@gmail.com on 4 Mar 2015 at 12:21

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GoogleCodeExporter commented 9 years ago 
I was able to replicate this problem given your data files that you shared 
(thanks for that). I uncovered two kinds of problems. The first is a problem 
with the data. The second is a problem with the results.
1.  In three of the files, I found one reader (#8) had no signal present data 
and another reader (#16) had no signal absent data. I noticed this when I first 
checked “Input Statistics Charts”. These readers had half the number of 
observations as the other readers. That alone may be ok, but when I checked the 
“Show Study Design”, one reader was missing the first half of the data and 
another reader was missing the second half of the data.
2.  In the last of the files, the performance averaged over your readers in 
modality “3” was near perfect, 0.98: two of the readers had perfect AUC, 
three had AUC 0.997, and one had AUC 0.993. iMRMC cannot handle this. You may 
be able to refer to Obuchowski2002_Acad-Radiol_v09p526, but I’m not ready to 
analyze this data. Regrets. You do not want to run studies where you get 
perfect performance; AUC has a limited useful dynamic range.

Original comment by Brandon.Gallas on 7 Mar 2015 at 5:51

GoogleCodeExporter commented 9 years ago

Original comment by Brandon.Gallas on 23 Mar 2015 at 8:19

GoogleCodeExporter commented 9 years ago 
Removing priority so that answered questions go to the bottom of the issues 
list.

Original comment by Brandon.Gallas on 25 Mar 2015 at 5:48