Higher-order composite scores (such as global or total scores) may also be appropriate when factors themselves are correlated and theoretically related.
Two common methods for calculating composite scores are:
- Unit weighted - each item is equally weighted, e.g., X = mean (A, B, C, D)
- Regression-weighted - each item is weighted according to its factor loading, e.g., X = .5*A + 0.4*B + 0.4*C + 0.3*D
In most situations, you can use either unit-weighted or regression-weighted composite scores. Regression-weighted scores are, technically, more valid. However regression-weighted scores are standardised (to a mean of 0 and SD of 1), so in some situations e.g., comparisons between means of two or more composite scores (e.g., for an RM ANOVA or Mixed ANOVA), unit-weighted scores should be used. But regression-weighted are appropriate for MLR and some ANOVAs, as well as many other types of statistical analysis.