So let’s get back to some politics, for a little while at least.

Lots of ink has been spilled about what’s going on with the Democrats

right now, as they focus on selecting a candidate to run against Bush

in the general election, and much of the discussion has centered on the

focus on electability and what the Democrats “should” be doing.

I’d like to talk about why the discussion of electability in the

Democratic candidate is reasonable and probably valuable to have.

In political science, we have a theory that applies very well to

two-party systems such as ours, called the median voter theorem.

(It can also apply to multi-party systems, with simple

modifications.) What it says, in brief, is that in a two-party

system, the “median voter” will win. Imagine, if you will, a

line, representing the ideological spectrum from left-to-right.

We can place every voter in our system along this spectrum. The

voter who falls in the middle of the spectrum (not ideologically, but

the one with equal numbers of voters on either side of him or her) is

the “median voter,” and in a two-party system, the party that gets this

voter will win an election.

(Note to my professional colleagues: This is not intended to be a

formal demonstration of the MVT — I could do that, but many of you

could do it better. I’m just trying to explain it stylistically

and show a general readership how it might apply to what we’re facing

in the elections right now.)

(Note to those interested: more formal definitions and discussion of this theorem can be found here, here, and here.)

Let’s consider a simple system of seven voters, as in this illustration.

There are seven voters here. The way this works is that voters

will pick the candidate closest to them on the preference

spectrum. Whoever captures four (or more) of the voters will win

the election issue here. So place two candidates anywhere you

like in the spectrum. One of them will be “closer” on the

spectrum to a majority of the voters, and that’s the candidate who will

win. We like to call this “capturing the median voter,” for the

candidate who captures the exact middle person — or the 50 percent

plus one voter, as you may have learned in a civics class — will

win. Another diagram will make this a bit clearer.

In this illustration, we’ve got a more complete system. Same diagram

as above, but now I have added candidates (1 and 2), a vertical line to

represent the exact middle of the preference spectrum (the bright green

line — you could consider it the dividing line between left and right,

or you can call it the “center”), and a thing called the tipping point

(which we will ignore for now).

Who will win the election? Remember, whichever candidate is

closer to the majority of voters, whoever can convince the median voter

to vote for him, he will be the winner. Once a candidate is close

enough to the median voter to convince this voter to select the

candidate, the candidate will also be even closer to a bunch of other

voters. Median voters are powerful, in a sense, because capturing

them produces an electoral majority. So if you’re a candidate,

you want to get the median voter to vote for you, because everyone else

to your side of the median voter will also vote for you.

In this election, candidate 2 wins. He is closer to the median

voter than candidate 1, so the median voter will choose to vote for 2

over 1, as 2’s preferences (which you might consider as “positions on

the issues”) are closer to the median voter’s than 1’s are.

Now take a look at this thing I have called the “tipping point.”

This

represents a point equally as distant from the median voter as

candidate 2 is. In other words, the distance from the median

voter to

the tipping point is the same as the distance from the median voter to

candidate 2. In order for candidate 1 to win, he will have to

come to the right of the tipping point, to get closer to the median

voter than candidate 1 is.

Can you guess how we might explain the tendency for both major

political parties in the US to look fairly similar, even on the

abbreviated ideological system that exists in this country? Yeah,

in pursuit of the median voter (who, in electoral opinion surveys of

the US, we have found is pretty much in the middle of the road

ideologically), the two parties have generally moved toward the middle

in pursuit of the MV.

Note some interesting features of this system: First, the

system

is somewhat middle of the road, as four of the seven voters could be

chracterized as preferring outcomes in the middle 50 percent of the

spectrum. Second, note that candidate 1 is closer to the (green)

center than candidate 2. Also note that the median voter is

pretty close to the middle of the system. Even so, the candidate

of the right will win, because his preferences are closer to those of

more of the people in the system.

O.K., so what does this mean for the current election? Here’s

what I think the election looks like to your average Democratic voter

right now.

Cand Right is George W. Bush. Candidates Left and Center-Left are

currently running in the Democratic primaries. If you are a

Democratic primary voter, and you think the election in November will

be close, you want to find the candidate who will come closer to the

median voter (whom I have located in the middle of the scale only for

convenience) than George W. Bush will. Candidate Left is just

about as far away from the MV as Candidate Right is. If your

estimation of the location of the median voter is off, you could lose

the election, and since we’re talking about a possibly close election,

you don’t want to be off. So you might choose to take someone who

doesn’t entirely match your own preferences (e.g., the cadidate is more

to the right than you are) in preference to having Candidate Right win.

So what the Democrats are doing right now, as they pursue the more

“electable” candidate, may be more “rational” than voting purely for

the guy whom they prefer to all others. And they realize that

this is not a one-shot game — it’s got two stages. Democrats who

are thinking of who’s more “electable” are perhaps remembering that

they have to win a presidency, not just a nomination. Democrats

pursuing an “electability strategy” are acting out a very complex

analytical situation in a very intuitive way. For just about any

Democratic primary voter, any Democratic candidate is preferable to

George W. Bush, and if the electorate is so tightly divided, it might

do to start with lots of people closer in their preferences to a

party’s candidate (as would be the case with Candidate

Center-Left). Otherwise, in the case when Candidate Left runs as

the nominee, Democrats have a much harder job of positioning to do to

get the votes necessary to obtain their majority.

So the move toward Kerry is not surprising (to me, at least). It may

represent very rational action by large numbers of Democratic primary

voters. But let’s see what happens in Tuesday’s caucuses and

elections….

Caveats: Yeah, this isn’t a perfect model of our system, as we have an

electoral college, possible shifts in preferences by candidates and

voters over the course of the run-up to the election, and so

forth. But it’s a stylized and simplified version of a complex

story that, I think, helps us to understand a bit more what’s going on

out there.

Also, this doesn’t represent my preferences. =-)