This is computed as:

$$u_{composite}=\sqrt{\frac{\bar{\rho}_{i}\bar{u}^{2}k(k-1)+k\bar{u}^{2}}{\bar{\rho}_{a}k(k-1)+k}}$$

where \(u_{composite}\) is the composite u ratio, \(\bar{u}\) is the mean univariate u ratio, \(\bar{\rho}_{i}\) is the mean restricted correlation among variables,
\(\bar{\rho}_{a}\) is the mean unrestricted correlation among variables, and *k* is the number of variables in the composite.