Table 2.

Intra- and inter-operator variation analysis for manual ICV estimation

	Op1 (Phase I)	Op2 (Phase I)	Op1 (Phase II)	${\text{Δ}}_{op1}^1$	${\text{Δ}}_{op1}^2$	MRPA1	MRPA1
AD	1.4870 ± 0.16418*	1.4870 ± 0.16416	1.4870 ± 0.16418	p = 0.55	p = 0.23	0.002	0.004
AC	1.4609 ± 0.14444	1.4610 ± 0.14436	1.4609 ± 0.14446	p = 0.35	p = 0.33	0.002	0.014

*ICV (mm³) presented as mean ± standard deviation (a factor of 10⁶ has been taken from all values). Op1 (Phase I): ICV measurements performed by Op1 in phase I of the study; Op2 (Phase I): ICV measurements performed by Op2 in phase I of the study; Op1 (Phase II): ICV measurements performed by Op1 in phase II of the study; ${\text{Δ}}_{op1}^1$ is the result for testing the null hypothesis that the ICV measurements performed by Op1 (Phase I) is not significantly different from ICV measurements performed by Op1 (Phase II). ${\text{Δ}}_{op1}^2$ is the result for testing the null hypothesis that ICV measurement calculated manually by Op1 (Phase I) is not significantly different from ICV measurements done by Op2 (Phase II). Paired t-test is used. MRPAD₁: Mean related percentage of absolute difference between ICV measurements performed by Op1 in Phase I and Phase II which provides intra-operator error in manual ICV estimation. MRPAD₂: Mean related percentage of absolute difference between ICV measurements performed by Op1 and Op2 in Phase I which is related to inter-operator error; AD: Adult With Alzheimer's Disease subject group; AC: Adult Control subject group.