"If you feel like showing off, average everything into everything else and call it the Gross Index of Total Enemy Morale. This won't fool anyone who knows the propaganda business, and you won't be able to do anything with or about it, but you can hang it on a month-by-month chart in the front office, where visitors can be impressed at getting in on a military secret. (Incidentally, if some smart enemy agent sees it and reports it back, enemy intelligence experts will go mad trying to figure out just how you got that figure. It's like the old joke that the average American is ten-elevenths White, 52% female, and always slightly pregnant.)"

It seems you simply can't win when you need to guard against mindlessly selfish behaviour.

Either that or let AI sort it all out.