Table 1. Cronbach's α scores for each subsection of the inventory for the control and clinical cohorts.

Subsection	No. of questions	Cronbach's α-controls	Cronbach's α-patients
1. Visual fields	13	0.91	0.81
2. Perception of movement	5	0.95	0.81
3. Search	9	0.98	0.71
4. Guidance of movement	11	0.68	0.77
5. Attention	4	0.98	0.56a
6. Crowded scenes	4	1.0	0.82
7. Recognition and navigation	7	1.0	0.77

Scores below 0.7 suggest more than one trait is being investigated by the questions in the subsection, whereas scores above 0.9 suggest redundancy, with questions investigating the same traits.

^aThis value became 0.79 on removal of two redundant questions. Within the control group, there was a high degree of redundancy (α values >0.9) for all sections, except for guidance of movement.