Example of SIBTEST nonlinear regression correction applied to the logistic regression method of DIF detection (DeMars 2014, personal communication)
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I am truly indebted to Christine E. DeMars (2009) who took the time to explicit the nasty formulas proposed by Jiang & Stout (1998). The use of regressed true score is preferable than using the mere observed score because a less-than-perfect (test) reliability, the latent score between groups would not be perfectly matched even when the observed scores were. In such a case, there is an inflated type 1 error, with spurious DIFs detected due to imperfect latent score matching between the groups examined. Below is the procedure to apply SIBTEST non-linear correction because the observed and true scores are not expected to be correlated linearly in presence of guessing. Specifically, it's the example as can be applied to the Wordsum test (10 items, Word A from J). The x=10 denotes the level of ability indexed by total score.
Example of SIBTEST nonlinear regression correction applied to the logistic regression method of DIF detection (DeMars 2014, personal communication)
Example of SIBTEST nonlinear regression…
Example of SIBTEST nonlinear regression correction applied to the logistic regression method of DIF detection (DeMars 2014, personal communication)
I am truly indebted to Christine E. DeMars (2009) who took the time to explicit the nasty formulas proposed by Jiang & Stout (1998). The use of regressed true score is preferable than using the mere observed score because a less-than-perfect (test) reliability, the latent score between groups would not be perfectly matched even when the observed scores were. In such a case, there is an inflated type 1 error, with spurious DIFs detected due to imperfect latent score matching between the groups examined. Below is the procedure to apply SIBTEST non-linear correction because the observed and true scores are not expected to be correlated linearly in presence of guessing. Specifically, it's the example as can be applied to the Wordsum test (10 items, Word A from J). The x=10 denotes the level of ability indexed by total score.