The studies I've seen failed to take into account that the difference between no penalty (not getting caught) and one year in prison is (usually much) greater t

The studies I've seen failed to take into account that the difference between no penalty (not getting caught) and one year in prison is (usually much) greater than the difference between N and N+1 years, never mind more subtle issues. Or, as biztos brings up, mostly looked at criminals who weren't making a considered decision in the first place.