There are no exact sciences of human behaviour. Economics, criminology, sociology, and the many branches of psychology are amenable to study through statistics but their results are invariably subject to different interpretations by different experts in their fields and it is clear that there are never experiments which can resolve disputes in the way there have often been in physics and chemistry. We should think hard about why this is so.
Goodhart’s Law can be expressed in a number of ways. My preferred way is “Any robust statistical pattern breaks down when people rely upon for it for forecasting.” Why is this so? Its consequences are more obvious. For instance it is extremely difficult to get rich by backing horses, or investing on the stock exchange. It is impossible to predict with certainty reoffending behaviour in the criminally insane. This problem was captured for all time by the long time director of Broadmoor Hospital, Patrick McGrath whom I met once as a young psychiatrist when I went there. He said “We all know half the patients in Broadmoor could be released, the trouble is we don’t know which half.” Returning to Goodhart’s Law, reductionists think it is just a matter of complexity. I totally disagree. It is to do with intentional/volitional behaviour. Here is a poem which approaches this issue from the direction of the staggering unpredictability of the future.
Distance means time, I suppose, and a long way off the boy standing in the boat by the further bank cannot see the man and woman alone at the open window, unless of course it is himself painfully present only years later on. Even so, though the boat travels back and forth memory and imagination the round trip, its a conceit: out and back are not the same and our imaginings use the elements of what we already are however rearranged and concealed from ourselves. The looking back makes out young hopes and fears but the casting off misses utterly the agony of regret.