Available with Spatial Analyst license.
The input raster bands to the classification must influence the categorization of the classification. The desired input bands are entered in a multiband raster and individual single band rasters.
Generally, the data for the input bands should be normally distributed for optimal results. If the data is not, you could apply a transformation to it.
The input bands should not be derived from one another. For example, some will argue that slope, aspect, curvature, and elevation should not all be input into the multivariate classification since slope, aspect, and curvature are all derived from elevation.