Table 1.

Study populations from which normative data were collected, statistical methods, and threshold strategies used to define cognitive impairment on the ECAS

	2SD-UK	2SD-NAC	QR-NAC
Study population	N=40 UK Controls	N=269 North American Controls (CALSNIC, CRiALS, PENN)
Statistical method	Mean ± 2 SD	Mean ± 2 SD	Quantile Regression
Threshold strategy	2 SDs below the mean*	2 SDs below the mean	5th percentile, adjusting for age and education

Note. SD = Standard deviation;

^*Cutoff values previously published⁵; NAC=North American Controls.