Table 2 Principal component analysis with varimax rotation of the cognitive variables.

Rotated component matrix	Component
	Attention	Verbal interaction	Verbal cognitive
Digit vigilance—correct detections	0.813	0.169	0.131
Choice RT log10 corrected	0.795	0.211	0.175
Digit vigilance—speed of detections	0.751	—	0.222
Simple RT log10 corrected	0.711	—	0.226
Digit vigilance—false alarms	0.564	0.122	—
Constructional praxis	0.509	0.151	0.334
Word‐finding difficulty	—	0.865	—
Spoken language ability	0.109	0.862	—
Comprehension	0.235	0.805	0.181
Remembering test instructions	0.397	0.564	0.280
Naming objects/fingers	—	—	0.720
Letter fluency: total correct responses	0.295	0.134	0.638
Serial 7's as a test of attention and calculation	0.131	—	0.602
Word recall	0.364	0.266	0.562
Word recognition	0.162	0.197	0.546

Extraction method: principal component analysis.

Rotation method: varimax with Kaiser normalisation.

Values in bold represent factor loadings >0.5.

—Indicate factor loadings <0.1.