Last night (11/4/2012) I took part in an interesting Radio 3 discussion programme called Night Waves . The first contributor, Jonathan Haidt, was fascinating and Ive just ordered his new book The Righteous Mind.
In the discussion he made a point that resonated with a problem that I have been wrestling with: discussing the relationship between reason and emotion he said, reason is mostly post hoc. Risk management decisions are taken pre hoc. They are decisions taken with insufficient information. They are decisions about an uncertain future. Post hoc, after the event/accident, there is usually much more information to which one can apply cause and effect reasoning. Before the event the links between causes and effects are either unknown or shrouded in estimates of probability, with large error bands attached. The information gap confronting a risk manager is readily filled by emotion – the natural instinctive state of mind deriving from ones circumstances, mood, or relationships with others.
Event Trees, beloved of engineers and project managers as a method for describing the risks associated with big projects, represent a denial of this reality (see Dangerous Trees?). All of the branching points on each limb of their trees must be assigned probabilities, usually with large error bands. By the time one reaches the tip ends of the branches the compound error bands are too large to fit on the page, so the magnitude of the uncertainty is ignored.
In the dangerous trees example just referred to an actual tree blew down and killed some one. In Britain, averaged over the whole country, the statistical risk of such a thing happening in a given year is about 1 in 10 million. Britains Health and Safety Executive describes risks of 1 in 1 million as adequately controlled. But after the event different sorts of reasoning are brought to bear. The police, who are predisposed to allocate blame in such circumstances, arrested the head estate warden and the estate manager on suspicion of negligent manslaughter. The coroner declared, a year and a half later, that all mature trees on the estates land adjacent to paths should be inspected and logged a requirement that, if applied to all the National Trusts properties (whose estate it was) might have bankrupted the institution.
Post hoc Event Trees are often transformed into Fault Trees that, with the aid of clear facts and reason, are transformed into trees with only one branch called culpable negligence. What pre hoc appeared a risk of 1 in 10 million, post hoc becomes a risk of 1 in 1.
After a year and a half the Crown Prosecution Service, dropped the case for lack of evidence, but a threat of dire consequence still hangs over the National Trust. Given the many millions of mature trees in Britain, the risk assessment and risk management implications of the coroners judgment, pursued to their logical conclusion would require the diversion of enormous resources to inspection and/or the execution of countless mature trees that could not be guaranteed 100 percent safe and who would offer that assurance in our litigious times? This experience is now colouring the (emotional?) judgment of Britains tree managers. In deciding what trees must be executed the legal risk now far outweighs the physical risk.