A recent story tells about McCain's focused ad spending in battleground states, and Obama's broader spending pattern. McCain is focusing on battleground states, while Obama is spreading resources more broadly.
Why the mismatch in strategies? Here I will give a quantitative argument that in terms of optimal resource allocation, both patterns of behavior make perfect sense, given the campaigns probably think their best strategies are for winning.
[Cross-posted at election.princeton.edu]
In a close election, resources are optimally spent on key battleground states. This is what Bush and Kerry both did in 2004. However, if the election is less close, then the candidate on top gets an advantage by putting his eggs in multiple baskets. If McCain's people think their only chance is to win by a small margin, they should focus on states they absolutely must have. In contrast, if Obama's people think the advantage they enjoyed until recently will return, they should spend more widely. Certainly the strategies they are pursuing are consistent with these points of view.
In 2004, I pointed out (as many did) that in a close election, resources were best deployed in states where the outcome is uncertain, with win probabilities between 20% and 80%. That campaign was quite closely fought, as evidenced by a plot of median EV estimate:
For most of the campaign, neither Kerry or Bush spent much time outside the 95% confidence band. The exceptions were a few weeks in August (when Kerry was definitively ahead, between the Democratic convention and the Swift Boat Veterans for Truth attacks) and September (when Bush was definitively ahead, between the Republican convention and the first debate). Therefore both candidates had a vital interest in the same battleground states, any of which could be critical to their efforts.
The disparity of influence by different voters could be quantified by a calculation of the expected win probability based on all available state polls - and how it would be changed by small shifts in voter sentiment. I defined the "jerseyvote," a measure of the power of an individual voter on influencing the election outcome, relative to a voter in New Jersey (me, for instance). By this measure voters in Pennsylvania, Ohio, and Florida had thousands of times as much power as I did. This suggested that activists should try to get out the vote in those states, and campaigns should advertise there - which they did.
This year, the dynamics are different. Until recently, Obama has spent the post-primary season clearly ahead of McCain:
For most of the last two months, Obama's 95% confidence interval has been entirely above the magic 269 EV threshold. For this reason I had to redefine voter power since when the race is not close, individual voters don't have much power anywhere. I redefined it as the amount of power that voters have if the race swings sufficiently to make either candidate's win probability 50%. One gets the expected suspects: Ohio (where one vote is currently worth 6350 jerseyvotes), Virginia (100 jerseyvotes), and so on (for more valuations click here). These match the places where McCain is spending the most money. What this suggests is that the McCain campaign is assuming that if they win, it will be tight. Therefore they are running a "Kerry/Bush" campaign, in which the goal is to get just over the threshold. They are not expecting a blowout; they just want to win.
In this same light the Obama campaign's spending suggests a more optimistic view. Their pattern of expenditures makes sense if they are assuming that they have many opportunities to win. In this scenario, voters in many states can potentially contribute to an electoral victory, and are worth pursuing. Such a strategy also allows the possibility of campaigning for downticket races in normally less-competitive states and districts, part of the 50-state strategy.
So despite Obama's recent slippage to near-parity, his campaign's spending makes sense if they believe that the recent decline in their candidate's fortunes is transient, and the advantage they enjoyed in July will return in the fall. They are acting as if they have enough eggs to put into multiple baskets.