IRT GRM model and DIF for Ordinal Polytomous data in R

Follow me on IG:   / musa_27469   📈 For rcode and dataset: https://gist.github.com/musa5237 Tutorial video of how to run the Item Response Theory (IRT) and detect Differential Item Functioning (i.e., bias items) for ordinal polytomous response data in R. Packages used are ltm and lordif. The model used is the Graded Response Model (GRM). Dataset are responses to the Generic Conspiracist Beliefs Scale (GCBS; Brotherton, French, and Pickering, 2013). The instrument is designed to measure degree of conspiracy theory beliefs. The goal was to measure the psychometric properties of the instrument and detect items in the instrument that may be more biased toward one gender.