1. As the description of Equation 2, it said "R is a population correlation matrix". What does it mean?
2. Through examined in this study, we recognize that common fit indices in SEM do not reflect the strength of unidimensionality. However, it seems that the application of factor strength indices are limited to bifactor cases. More complicated scenarios are worthy to investigate further.
3. Only continuous variables are considered here. In other words, the performance of factor strength indices for categorical responses, which may be applied by fitting a 2-parameter IRT model and observing discrimination parameters, is still unknown. At least, the number of indicators (items) may play an important role toward the calculated values.