The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor. Campbell's LawI've blogged before about Mickey Mouse micro-targets. Such targets are in common use today, and they obey Campbell's Law because they are so narrow that people can fulfil them in ways that conflict with society's best interests. Broader objectives, a feature of Social Policy Bonds, would help, because then people would have fewer opportunities to withdraw resources from the fulfilment of untargeted social goals to goals that are targeted. Broader goals also reduce the relative costs of monitoring compliance. But even so, it is best to think of metrics that actually are, or are inextricably correlated with, what we actually want to achieve. There are some things you can do to minimise the risk of gaming the system. For example: if our target is universal literacy in a country, we could take reading tests at a random sample of 50 out of a possible 1000 locations in that country. Similarly for pollution or crime, for examples. There might be other ways of targeting metrics without specifying in advance exactly what they are, so that people have to do the job, rather than game the system, in order to profit from holding Social Policy Bonds. But there will probably always be a need to see that people are complying with the spirit, not just the letter, of any target. That said, some targets would be pretty difficult to game: for instance, the goal of having no people killed by a military nuclear explosion over the next thirty years.