[Rasch] DIF and multiple comparisons - BH method

Fred Wolfe fwolfe at arthritis-research.org
Tue Feb 7 23:26:54 EST 2006


Hi Mike,

I am not expert on the Benjamina-Hochberg method. I understand that there 
are modifications of BH, but it seems that the original BH is still the 
predominant method now (from what I could see looking at the literature).

BH would seem to have important advantages over Bonferroni.

This issue came up when a colleague was examining DIF using non-Rasch 
methods. Using the model form: Item score = Exogenous variable + 
Questionnaire Total, this was examined by 3 methods (with different 
results) that had been used in the literature:

Partial gamma coefficient (Stata)
Kendal's tau b coefficient (SAS)
Variance estimation using bootstrap methods

Perhaps someone might have comments as to the usefulness/validity of Rasch 
vs. non-Rasch methods for detecting DIF.

Fred


At 04:45 PM 2/6/2006, Mike Linacre (RMT) wrote:
>Thank you, Randy and Fred,
>
>The Benjamini, Y. & Hochberg, Y. (1995) method for multiple comparisons 
>appears to be:
>(1) Compute individual p-values for each of the N hypothesis tests as 
>though each was the only one.
>(2) Sort the N p-values by size ascending, n=1,N, so that p(1) is the 
>smallest, and p(N) is the largest
>(3) Starting from p(N) downwards, look down for the first p(n) which is 
>less than or equal to (n/N) * 0.05 (or your chosen significance level)
>(4) Tests 1 to n are classified as significant.
>
>Is this correct? Have any useful modifications been proposed? This seems 
>easy to implement in software, which I may well do.
>
>Thanks again,
>
>Mike L.
>
>Mike Linacre
>Editor, Rasch Measurement Transactions
>rmt at rasch.org www.rasch.org/rmt/ Latest RMT: 19:3 Winter


Fred Wolfe
National Data Bank for Rheumatic Diseases
Wichita, Kansas
Tel (316) 263-2125     Fax (316) 263-0761
fwolfe at arthritis-research.org





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