Table 3.

Constrained principal component analysis (CPCA) results to explain variance in volumes of hippocampal subregions, tracts, basal ganglia, thalamus and amygdala in relation to neonatal clinical factors (NCF) and genotypes (G).

CPCA clinical and genotype variables	Overall	PC1	PC2	PC1 + PC2
Total variance	26.46	9.45	8.19	17.64
% variance	100.00	35.72	30.93	66.65
Variance explained by clinical variables and genotypes	13.79	6.87	5.32	12.19
% variance explained by clinical variables and genotypes	52.16	25.96	20.11	46.07
CPCA clinical × genotype interaction		PC NCFxG
Variance explained by clinical variables × genotypes interaction	4.72	1.34	–	1.34
% Variance explained by clinical variables × genotypes interaction	17.84	5.08	–	5.08

Each component accounts for a portion of the total variance: the first component accounts for the largest amount of variance, with each successive component accounting for a smaller amount of the total variance. PC1, principal component 1; PC2, principal component 2; PC1 + PC2, sum of PC1 and PC2; PC NFCxG, interaction term between neonatal clinical factors and genotypes.