Computes composite reliability (Raykov's rho / McDonald's omega) for a set of congeneric reflective indicators: $$\rho = \frac{(\sum \lambda_i)^2 \text{Var}(\eta)}{(\sum \lambda_i)^2 \text{Var}(\eta) + \sum \theta_i}$$ where \(\lambda_i\) are the unstandardized factor loadings and \(\theta_i\) are the indicator error (unique) variances.
References
Raykov T (1997). “Estimation of Composite Reliability for Congeneric Measures.” Applied Psychological Measurement, 21(2), 173–184. doi:10.1177/01466216970212006 .
McDonald RP (1999). Test Theory: A Unified Treatment. Lawrence Erlbaum Associates, Mahwah, NJ.