... multiplier has dropped substantially, largely because of the substantial increase in the import share of total consumption. I don't know off the top of my head of industry specific studies of multiplier effects, but there may be something by income level that could be tied back to industry level studies of income distribution.

So, no, I don't know but its a great question. As far as I can tell, Richard Florida gets his causality from rough correlation of a "Knowledge class" that does not seem to be very clearly defined independent of his line of argument.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.