ADNI subjects and biomarkers included in each study. Here we outline the subject samples analyzed for different classification tests. Subjects are split into independent training and testing samples approximately in a 3:1 ratio, except for the smaller studies, to ensure correct evaluation of classifier performance. The 3:1 ratio is used in several machine learning studies such as Vemuri et al. (2008a). MRI denotes that a 1.5T MRI scan was available; BMI denotes body mass index. CSF denotes that CSF-derived biomarkers were available