Error bar (mean ± STD) plots showing the trends in the variability of different ECG wave intervals (A, B) and SDI parameters (C, D) within the three groups. The arrow between the groups for a particular feature indicates that it can differentiate the groups with statistical significance. From panel (D), it is obvious that only the variability measures of beat-to-beat SDI parameter (vSDI TQ-RR ) can significantly differentiate all the three groups (CAN-, ECAN and DCAN) thus identifying the presence and progression of CAN. 5.4.1 Reproducibility of the SDI measure with ECG recording length variation An efficient measure should be reproducible at different data lengths. To evaluate the sensitivity of the SDI measures in CAN analysis with ECG data length, we calculated the values of different SDI measures by varying the length of ECG from 1 min to 5 min in addition to the results reported for a 10 min recording. The variation of the values of the SDI measures is shown in Figure 5-4. The values of mSDI QT-TQ and mSDI TQ-RR showed a consistent pattern in differentiating CAN-group form CAN positive groups (i.e. ECAN and DCAN) with ECG data length from 1 min up to 5 min and also for 10 min segment [Figure