Not evaluating, or evaluating poorly, will mean that policy makers will not be able to provide meaningful evidence in support of any claims they might wish to make about a policy’s effectiveness. Any such claims will be effectively unfounded. Whenever a policy was targeted on individuals who were outliers in some way (for example, prolific offenders, low educational attainers) a common hazard for the evaluator is regression to the mean. If assignment to the policy was based on a snapshot measure shortly before it began (for instance, the number of offences in the last month, or results in a recent school test) then the selection process will to some extent capture the results of temporary fluctuations in an individual’s life rather than underlying extremes.