Well, that's what we have statistics and the scientific method for.<p>Of course, that means lots of math, and lots of research, and lots of hard work, and having to actually to change your mind if your predictions are wrong, and--worst of all--it means not making simple, sound-bite pronouncements that fit someone's political agenda. You can't make a career writing editorials about how there's a 73% chance that raising taxes on widgets will reduce the annual productivity of the foobar industry by 1.3%.