How do you measure a changing market?
In yet another good read, Michael Lewis of "Moneyball" and "Liar's Poker" fame has written about the evolution of football in The Blind Side. In general its about game-changing events as they relate to a single position: the left offensive tackle. In particular its about a single individual who plays that position.
It also hints at the point that metrics only appear when the game changes in a substantive way.
If you ask how the defenses of the 50's, 60's and 70's compared to those of the 80's, 90's and 00's in terms of sacking the quarterback --- you're stuck. The NFL didn't keep individual sack statistics until 1982, which coincides with the advent of Lawrence Taylor (who didn't actually lead in that category until 1986) as the most feared player in football.
Multi-channel, integrated, or media neutral programs have changed the face of the market. What we don't quite yet have a handle on is how to measure the value of those campaigns. What metric reflects the impact of a campaign? Once we answer that, we could start a fantasy league for marketing.