“All scientific work is incomplete - whether it be observational or experimental. All scientific work is liable to be upset or modified by advancing knowledge. That does not confer upon us a freedom to ignore the knowledge we already have - or to postpone the action that it appears to demand at a given time. Who knows - asked Robert Browning - but the world may end tonight? True - but on available evidence most of us make ready to commute on 8:30 the next day.” Sir Austin Bradford Hill – as quoted in his landmark 1965 paper on causation.