Table 2. Variables' contributions to the two principal components (Cronbach's α, a measure by default for the internal consistency of categorical principal components in the SPSS software, is 0.891 and 0.721), absolute values above 0.500 were retained to define the principal components.

Variable	Principal component
	1 Cognition	2 Motor function
Cognitive status	0.891	−0.095
Maximal education level	0.884	−0.109
Education delay	0.840	−0.376
Education type of establishment	−0.814	−0.020
Age at initial symptoms	0.725	0.132
Initial symptoms	0.710	−0.353
Age at becoming chair-ridden	0.226	0.857
Age at first contractures in lower limbs	0.298	0.759
Age at loss of ambulation	−0.131	0.707
Delay of diagnosis	0.442	0.697