I think the only way to apply a metric while avoiding the consequences of the Law is to keep the metric secret. As soon as the subjects are aware of the metric,

I think the only way to apply a metric while avoiding the consequences of the Law is to keep the metric secret. As soon as the subjects are aware of the metric, they will try to optimize it, rather than the real performance that the metric is supposed to indicate. There is a close connection with security, say screening at airports. If you fail to keep your screening criteria secret, the terrorists will simply ensure that they do not match the criteria. One way to thwart this is through randomness. There is a long public debate between Sam Harris and Bruce Schneier where the latter tried in vain to explain this to the former, who insisted that it was a waste of resources to search little old ladies. If one of your metrics is “don’t search little old ladies”, the terrorists will discover this through time by observation. The next bomb will be carried by a little old lady.