Concept group alpha estimate unclear

[ekiebel]

When MCTest estimates alpha for a concept group as part of an overall exam, the value is much lower than when I submit just the concept group to an analysis. Is the overall test alpha somehow informing the value for the subgroup?

Also, could there be an option for handling missing data? As is, missing values are imputed as 0 (incorrect) which requires filtering before submitting the data for analysis. Without listwise deletion prior to analysis, large number of missing values (for, say, practice tests) result in heavily-biased parameter estimates