[Rasch] DIF and multiple comparisons - BH method

Randy and Shelley MacIntosh srmac at saber.net
Tue Feb 7 08:03:15 EST 2006

This would be a welcome addition to Winsteps. But you will have to carry
out the computation of the t- and p-values to 4 or 5 (or more) decimal
places to permit its use when you have many items and groups.

To: rasch at acer.edu.au
From: "Mike Linacre (RMT)" <rmt at rasch.org>
In-Reply-To: <43e7782e.3ec4.0 at saber.net>
Mime-Version: 1.0

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

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