Karl Smith believes that "overwhelmingly the presumption should be that epidemics have a single precipitating factor." He applies "epidemic" broadly:
People are sometimes confused by the fact that complex conditions have a long list of necessary factors. However, the odds against more than one necessary factor pushing the phenomenon across the line into epidemic at the exact same time are astronomical. Not to go to far astray but this is why recessions likely have a single precipitating factor. They spread too fast and burn out too quickly to be multi-casual. A fifty year period of off and on stagnation, that might be multi-causal. An 18% collapse in industrial production over 18 months? That has a vector.
The Dish 