Auf Noahpinion steht seit vorgestern eine Abrechnung mit RBC-Modellen (Real Business Cycle Modellen), die sehr lesenswert - um nicht zu sagen amüsant - ist.Noah Smith zeigt darin nochmal anschaulich dar, in welchen Punkten diese Modelle (die lange Zeit die Modelle der Makroökonomie waren) an der Realität vorbeigehen.
Dann ist es auch kein Wunder, dass diese Modelle schlechte Prognosen liefern:"It has often been said of the Holy Roman Empire that it was "neither Holy, nor Roman, nor an Empire." However, that joke has gotten a bit stale since Voltaire wrote it in the 1700s, so I think it's time for a new one. Real Business Cycle models, it turns out, are neither Real, nor about Business, nor about Cycles."
"Basically, here's how an RBC model works. You take every factor of production you can measure - capital, labor, inventories, etc. - and you factor it out, and then you're left with the part of production you can't explain, which is called the "residual". You then label this residual "technology", and you assume that it moves according to some sort of simple stochastic process - for example, an AR(1). The rest of the model is just a description of the ways in which the rest of the economy responds to that AR(1) technology "process". In RBC models, this response is usually as simple and uninteresting as possible; pretty much everything is driven by the uber-simplistic movement of "technology".
In other words, if I want to make a forecast using an RBC model, that forecast will be based on the assumption about tomorrow's level of "technology" - i.e. the part of the model that doesn't come from data we can directly measure - and that level, in turn, will be "predicted" by nothing more than the simplest stochastic equation imaginable!"