TABLE 2.

Mean ± standard deviation of ICC and MAE from the tracer head‐to‐head comparison.

			FreeSurfer ROI
	Global summary		All ROI		Summary cortical ROI		Other cortical ROI		Subcortical ROI
Harmonization method	ICC	MAE	ICC	MAE	ICC	MAE	ICC	MAE	ICC	MAE
Unharmonized	0.882	0.101 ± 0.076	0.819 ± 0.077	0.111 ± 0.029	0.866 ± 0.03	0.113 ± 0.023	0.838 ± 0.048	0.109 ± 0.031	0.701 ± 0.089	0.12 ± 0.028
Centiloid, scaled	0.912	0.088 ± 0.075	0.811 ± 0.098	0.112 ± 0.032	0.891 ± 0.018	0.099 ± 0.02**	0.822 ± 0.063	0.116 ± 0.037	0.686 ± 0.137	0.11 ± 0.019
ComBat, no covariates	0.916	0.08 ± 0.075 *	0.838 ± 0.083 ****	0.086 ± 0.019 ****	0.899 ± 0.018 **	0.089 ± 0.014 **	0.853 ± 0.05 ****	0.084 ± 0.019 ****	0.72 ± 0.111	0.09 ± 0.021 *
ComBat + age, sex, APOE	0.898	0.099 ± 0.075	0.827 ± 0.08 ****	0.095 ± 0.023 ****	0.881 ± 0.024**	0.106 ± 0.017	0.844 ± 0.049***	0.093 ± 0.024**	0.707 ± 0.099	0.092 ± 0.022
GAM‐ComBat + age, sex, APOE	0.897	0.1 ± 0.075	0.827 ± 0.08 ****	0.095 ± 0.023 ****	0.881 ± 0.024**	0.107 ± 0.017	0.844 ± 0.049***	0.093 ± 0.024**	0.707 ± 0.099	0.092 ± 0.022
PEACE, no covariates	0.897	0.092 ± 0.077**	0.813 ± 0.087	0.097 ± 0.022 ****	0.875 ± 0.027	0.103 ± 0.019	0.831 ± 0.058	0.093 ± 0.021**	0.684 ± 0.094	0.104 ± 0.027
PEACE + age, sex, APOE	0.884	0.083 ± 0.095**	0.822 ± 0.079	0.086 ± 0.021 ****	0.867 ± 0.028	0.094 ± 0.018*	0.842 ± 0.05*	0.083 ± 0.021 ****	0.698 ± 0.087	0.092 ± 0.022

Note: The mean across scan pairs was computed for the global summary region, whereas the mean across ROIs was computed for the FreeSurfer ROI. Bold values indicate the best performing harmonization method. Asterisks indicate statistical significance of paired t‐tests comparing each harmonization method with unharmonized.

^* p < 0.05.

^** p < 0.01.

^*** p < 0.005.

^**** p < 1e‐4.