Fig. 1

Clusters of conversion time in patients with mild cognitive impairment who converted to Alzheimer’s disease during follow-up (group A). Calinski-Harabasz and Silhouette evaluations suggested an optimal number of three clusters plus an outlier (indicated as cluster 4). Conversion time cutoff estimations are (in days): 1000 (between clusters 1 and 2) and 1550 (between clusters 2 and 3). The majority of patients (n = 76) converted to dementia within 27 months and were included in the first cluster. Given the numerical predominance of this conversion time-based group with respect to the others, we labeled the group as “typical Alzheimer’s disease,” whereas we considered patients belonging to clusters 2, 3, and 4 as late-converter patients