Thursday, November 4, 2010

Winsteps Item Most Unexpected Responses

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A companion table to person most unexpected responses (Table 6.5) drawn from Winsteps Table 17.1 Person Statistics is the table of item most unexpected responses drawn from Table 13.1 Item Statistics.

The data from three columns in Table 13.1 are re-tabled into Winsteps Table 10.5 Most Unexpected Responses.

 These values are plotted, in red, on PUP Table 3. 

Item 11, with an estimated IRT difficulty measure of -1.51, is the easiest question any student missed, by Murta. Item 2, with an estimated IRT difficulty measure of 1.14, is the most difficult question with an unexpected response, by Martin. This rank of unexpected responses is again directly related to item difficulty on PUP Table 3. This makes good sense.

Difficult questions are expected to receive wrong marks. No wrong marks are expected on easy questions. High ability students are expected to mark difficult items correctly. These are basic expectations for IRT.

Of interest here is that the locations of the most unexpected responses for person and for item are identical on PUP Table 3. The person scan of PUP Table 3 is from highest score to lowest score, vertically, and the item scan of the table is from easiest to most difficult, horizontally.

These most unexpected responses are calculated on average and in general, as is characteristic of right mark scoring (RMS). The test instructions are to mark the best answer on every question. Students are not given the responsibility, and a reward, for reporting, on each specific question, what they know and do not know, as is done with Knowledge and Judgment ScoringTM (KJS).

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