Estimated mean ± SD NAA concentrations at each institution.

Institution	Subjects	Scanner Field, Manufacturer, Model	Mean WBNAA (mmol/L)	SD (Unadjusted) (mmol/L)	SD (adjusted)
First	n = 23	1.5 T, Siemens, Vision	11.7	1.3	1.3
Second	n = 31	1.5 T, Siemens, SP63	12.3	1.1	1.1
Third	n = 24	1.5 T, Siemens, Vision	12.6	1.2	1.2
	n = 12	3.0 T, Siemens, Trio	11.7	1.1	1.1
Fourth	n = 11	4.0 T, GE, Signa 5.x	12.8	1.5	1.5
Total	n = 101		12.2^*	1.2^*	1.2

Note:—WBNAA indicates whole-brain N-acetylaspartate. The SDs are presented as both unadjusted and adjusted with respect to confounding effects from age and gender (differences were in second decimal digit or smaller).
* Average of all subjects at all institutions.