Bias (in number of voxels) and standard deviation (SD) of ROA size estimate as a function of width of the two square ROAs or the mean of the activated voxels. There are two ROAs so the total number of truly active voxels in the bias calculation is twice the number of voxels in each square ROA. (a) Bias as a function of the width of the two square ROAs, with activation mean δ = 2.25. (b) Bias as a function of the mean of the activated voxels, δ, using two 7 by 7 square ROAs. (c) SD as a function of the width of the two square ROAs, with activation mean δ = 2.25. (d) SD as a function of the mean of the activated voxels, δ, using two 7 by 7 square ROAs.