Jeney,
This is the response I got from a senior psychometrician with an organization I work for ...hope it helps. Everyone should have one of these people at their institution in one form or another.
Ken
Hey Ken,
If your group is that large (i.e., n=350), then I am of the opinion that 2%-3% could be a good guideline. There are other considerations though. If your questions have 4 options (instead of the 5 like we do), 1 of which is the correct answer, then there are 3 distractors. If 2 of these distractors are attracting only 1%, then you can't very well discard them both since this would leave you with 2 options which is now a true/false item. Another consideration is the discrimination (if you have access to a program that outputs these for every option). If you have 2 distractors that attract 3% and you can't afford to discard both, then I would look at the distractor that discriminates positively and discard that one (we like to see the correct answer to discriminate positively and the distractors to discriminate negatively).
Hope this helps.
Sincerely,
Dr. Ken Kontio B.Sc., M.D., M.Ed., FRCS(C)
Department of Surgery - Rm 3342
Children's Hospital of Eastern Ontario
401 Smyth Road
Ottawa, ON
K1H 8L1
Office (613) 737-7600 x 2426
Fax (613) 738-4840
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