Principal component analysis was not applied to the data set corresponding to the entire age range because the use of PCA on the individual age ranges revealed that the first components varied considerably across the age ranges. Application of PCA to the entire age range would have identified components which were only remotely interpretable compared to the components identified in the individual age ranges. Instead the seven data sets consisting of the effect sizes for individual phenotypes as determined by the age range averaging described in section 8.3.2 were used in the analysis.
