Figure 1.
BPM Design Matrix. In the hypothetical ANCOVA models demonstrated here the first 2 columns represent 2 hypothetical study populations and column 3 represents a nuisance regressor. This third column demonstrates the difference between a traditional SPM analysis and the BPM approach. A). In a standard SPM-style analysis all voxels have the same design matrix, where the nuisance regressor represents some scalar value (e.g. mean gray matter volume within an ROI). Note that the model is exactly the same in the different brain regions. B). In a BPM analysis, each voxel has a unique design matrix. In the example shown here, the values in column 3 represent the corresponding gray matter volume voxel-values. Since the gray matter volume values are different in various brain regions, the design matrix is unique at each voxel.