Reliability
MCI
DISEASE
Internal consistency reliability (i.e., the extent to which individual items within an instrument correlate with each other to form a multi-item scale) was assessed at baseline and month 36 using item-total correlations, with a target significant correlation > 0.30 indicating good homogeneity [Test–retest reliability (i.e., the extent to which a measure yields consistent scores within the same patient each time it is administered) was assessed between baseline and month 6 (given the study design) among stable patients. Stability was defined in two ways: patients with no change in each of a) MCI-CGIC, GDS, and CDR-SB; or alternatively b) MCI-CGIC, GDS, and MMSE. As test–retest reliability is typically assessed across shorter time periods where there can be a strong rationale for disease stability (e.g., a few days to two weeks between measurement timepoints), we sought assurance that the disease was stable. Therefore a three-component definition was employed using 1) a disease-specific assessment of global disease severity (MCI-CGIC), 2) a non-disease-specific global measure of disease severity (GDS) and 3) a detailed measure of disease severity (CDR-SB or MMSE). We examined both the CDR-SB and MMSE as we proposed the CDR-SB to be the more accurate measure of disease severity and the MMSE to be a measure with more widespread use (but higher variability in the MCI population). Mean differences and paired t-tests were calculated to compare ADCS-ADL-MCI total scores (and the statistical significance of any change) between the two assessment visits. To assess test–retest reliability, the intraclass correlation coefficients (ICC) was computed where ≥ 0.7 indicates good reproducibility [