unitguess

The unit for the test statistics for presence of guessing (Haberman, 2006). These tests are performed on dichotomous items (). Under the fitted model, the test statistic for an item has an approximate standard normal distribution. Under Equations 40 and 41, the test statistic approaches with probability 1 as the sample size increases. For an example, see listening8.txt, where unitguess is 11, and the corresponding output file listeningguess.csv. The adjusted residual is the test statistic. In the example, items are present with significant evidence against the 2PL model. For items 29 and 30, which have positive adjusted residuals that exceed 10, certainly might be better fit by a 3PL model rather than a 2PL model. On the other hand, items 5 and 6 may suggest a problem with the 2PL model that does not indicate any benefit from a 3PL model, for the adjusted residuals are negative.