Function Item Factor Analysis -> FA-Based Item Analysis and omega reliability estimation.
The IFA function (a) assesses the dimensionality of a set of items according to the linear factor analysis (FA) model, (b) performs item and scale analysis on the basis of the unidimensional FA sub-model, and (c) estimates the reliability of the test scores with the omega coefficient.
The function contains two computing sub-functions: (a) Item appropriateness, which assess the appropriateness of the data and the unidimensionality assumption, and (b) item factor analysis, which performs unidimensional FA-based item analysis for the set of items.
The results displayed in the item-analysis output are the item means (difficulty indices), the standardized factor loadings (item discriminations) and the squared factor loadings (item reliabilities). Finally, IFA provides the omega reliability estimate for the test scores together with its 90% confidence interval. The only information it needs are the items that will be used for the analysis.
Download example data file: Item_factor_analysis.zip