Jack these type of studies drive me nuts! Wringing our hands over such clinical maxims is useful to a point but calling fro quantitative evidence to validate such pearls is largely nonsense. Red flags should merely make us THINK! I do not believe that every diagnosis in this area or others can be approach quantitatively or in a Baysean manner. Some conditions are just to important to ignore (i.e. they are MUST RULE OUTS) particular when clinical judgement suggests their presence. For example fever is a woefully non-specific sign but in the setting of back pain makes me very concerned over infection or cancer. Of course not every fever plus back pain is sinister in origin. Red flags should make people play being a doctor. They should raise a warning. Red flags need not trigger critical pathways but they should break you out of automatic pilot mode.. Remember that critical paths are great if you are on the road and not in the woods Lenny Calabrese