[Rasch] missing data advice needed

Fidelman, Carolyn Carolyn.Fidelman at ed.gov
Tue Jan 4 09:50:44 EST 2011


Hi All,

I have a burning question about treatment of item-level missing data. Imagine a short reading or math screener given to 5 year olds (individual administration format, of course) in order to place them on some quick proficiency scale.  The 20 items are designed to go from easy to hard. Because young children can become easily frustrated and burdened once they reach their level, a stop rule is in place in which the administrator ceases testing once the child has missed 5 items in a row.

My question: is it legit to impute 0s to the missing values (9s) of a record such as

1110100110000099999

thus making it

1110100110000000000

where the assumption is that the child would not have correctly answered those last few items had they been administered anyway?

I know that for WINSTEPS and Rasch analysis, missing values are not an issue.  I'm really thinking in terms of the descriptive statistics that precede them in a report. It seems more reasonable for purposes of comparison to report for a set of 1000 examinees  that the p value of, say, Item 18 is  .09 where n=1000, than to say it is .25 for the 200 examinees who were actually presented with the item.

Or should I just have two different datasets, one for the Rasch analysis (leaving the 9s) and another for the descriptives (imputing 0s for 9s)?

Your wisdom much appreciated!  (and Happy New Year!)

Carolyn


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