Suppose that you want to rank the members of a set X = {x1, x2, x3, x4} relative to each other. You can, say, assign x1 = 40, x2 = 30, x3 = 20, and x4 = 10 by some measurement metric Y. Or, you can assign x1 = 80, x2 = 60, x3 = 40, and x4 = 20. Or you can assign x1 = 4, x2 = 3….
No matter which one you choose, as long as the metrics are all multiples of each other, the elements of the set are still in the same position relative to each other (which is all we care about, by assumption). In math-speak, the measurement metric Y is invariant under a positive linear map, as the important properties don’t change when you throw in arbitrary constants. It’s generally inconvenient to use huge constants, so people usually renormalize Y to some neat number, such as 1 or 100.
Humans, however, aren’t born with this kind of math built in, and so you can pull tricks by failing to renormalize. Very few people will notice if your percentages add up to 105%. Without quantitative analysis, it’s even worse, as you can use qualifiers (”important”, “big”, “profitable”, “useful”, etc.) to stop people from renormalizing without setting off alarm bells. This is a very, very old trick; the best way to counter it, generally, is to quantify the metric and then make sure it’s renormalized during every step. Some cases where this comes in handy:
- Probability. For reasons of mathematical sanity, probabilities are always renormalized to 1, although there are some cases where you can get away with other numbers (eg, Bayes’ Theorem still gives the same result if you multiply the prior by 100). Nevertheless, quacks worldwide still fail to renormalize by claiming that they predicted every result with high accuracy.
- Utility. Utility functions are invariant under positive linear maps, and they can generally be renormalized to whatever you like (finite numbers are usually necessary, as explained here). Making your life wonderful by assigning a high utility to everything is the same mistake as an amateur economist failing to account for opportunity costs.
- Priority. If you generalize priority to quantity of resources allocated, rather than using a simple preference ranking, it should be invariant. I am still stunned by how many managers insist that every task is extremely important; this corresponds to a crisis of Bayesian affirmation.
- Grades of all varieties. Failure to renormalize is well known as grade inflation. Note that renormalization is not bell curve grading; it corresponds to, say, the fungibility of x/4.0 GPAs and x/100 averages.
- Competitions of all varieties. Professional sports are generally immune to renormalization failures, as there can obviously be only ten teams in the top ten. However, this phenomenon is rampant on school sports teams, thanks to the “self esteem” culture.