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st: RE: RE: reliability with ordinal data-Kendall's w?


From   Nick Cox <[email protected]>
To   "'[email protected]'" <[email protected]>
Subject   st: RE: RE: reliability with ordinal data-Kendall's w?
Date   Tue, 14 Dec 2010 11:55:42 +0000

On the graphics, 

. webuse rate2
(Altman p. 403)

. tabplot rad?, percent showval

gives an example of -tabplot- (SSC) with such data. 

Nick 
[email protected] 

Nick Cox


[...] -tabplot- from SSC offers one of various graphical alternatives. Diagonal agreement and off-diagonal disagreement will be pretty clear. 

Ploutz-Snyder, Robert (JSC-SK)[USRA]

I need to perform a reliability analysis among two raters who rated the same observations independently.  Observations are rated on an ordinal scale, taking 4 distinct values in increasing order.  Neither rater is assumed the "gold standard."  There are a LOT of ties in my dataset (a good thing in terms of rater reliability).

I came across some web hits about Kendall's W, which is different from the more familiar tau.  Can anyone attest to whether this is the best way to go about a reliability analysis with ordinal data?   Is there a way to implement on Stata?? How does W differ from tau, and Somer's d??  

Are there other/better methods that I should be considering too?

Also--for those knowledgeable about reliability analyses... I think that eventually I would like to graph these data with something akin to the Bland-Altman plots.  Do you take issue with that approach given that the data are not continuous?  Are the BA Limits of Agreement valid in this situation??


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