I'm reading Butterfly Economics (by Paul Ormerod) and I'm a bit perplexed about his statements on the practical impossibility of predictions in economics. I understand and since I have very little information I believe him that prediction about for example GDP growth are generally erroneous, however this stance makes the work of financial state departments, national banks or any other economic policy maker institution susceptible. On the other hand any argument stating that the persons are bad economists making such and such predictions that prove to be wrong, these statement are necessarily false, since nobody could make faithful predictions except by chance.

However I believe that there are better and worse economic predictions. There are analysts who may say more informative statements on the rationally expectable economic situation. Ormerod's argument is slippery since he treats predictions as genuine bivalent propositions, but economists using them simply do not treat these as such. Economists usually (as I understand) assign probability to such statements, moreover they are baysian with respect to these. So if there is a prediction that is assigned higher probability by the majority of the expert economists, it is rightfully said credible, but not true in any way.