[Rasch] Differential Item Functioning: Help Needed
rense.lange at gmail.com
Wed Feb 6 17:53:27 EST 2013
About right - but I haven't seen enough dif > 1 logit to be sure about the larger differences. These are binary items, correct?
On Feb 6, 2013, at 12:05 AM, Mike Linacre <rmt at rasch.org> wrote:
> Here is a DIF nomogram showing the Reference and Focal group sizes to
> obtain p=.05 statistical significance with various logit sizes of DIF on
> dichotomous items (MCQs, etc.). For example, the nomogram indicates we
> need groups of around 100 to detect DIF of 1 logit, and groups of about
> 1500 (log-scaled) to detect DIF of 0.25 logits.
> It is based on statistical theory, but with approximations and assumptions.
> Does it match your experience? Are the indicated group sizes too small,
> too large or about right?
> Mike L.
> DIF Nomogram is at http://www.winsteps.com/a/difnomogram.png
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