Bibliography (6):

1. The Rediscovery of Bifactor Measurement Models

2. Bifactor and Hierarchical Models: Specification, Inference, and Interpretation

3. Scientific and Social Importance of Assessing Individual Differences: ‘Sinking Shafts at a Few Critical Points’

4. Wikipedia Bibliography:

   1. https://en.wikipedia.org/wiki/R._B._Cattell

      https://en.wikipedia.org/wiki/R._B._Cattell

   2. Structural equation modeling

   3. Factor analysis