Poll Analysis: Seattle Mayor and King Co. Exec.

Darryl Holman is a UW professor who knows his numbers. Apparently, in order to get his Ph.D. in anthropology, he had to take a bunch of math classes in college:
Poll Analysis--Seattle Mayoral Race:

A new KING-5/Survey USA poll in the Seattle Mayoral Race was released today. This race has Mike McGinn facing off against Joe Mallahan. Just last week, a Washington Poll poll had Mallahan leading McGinn by 44% to 36% with 20% undecided. The results suggested that Mallahan had an 89.9% probability of winning.

Today’s poll of 586 people (taken over the weekend) shows a tighter race with Mallahan leading McGinn by 45% to 43%. A Monte Carlo analysis (methods) consisting of 1,000,000 simulated elections using the proportions and sample size observed in this poll shows Mallahan winning 635,831 times and McGinn winning 352,638 times. Statistically, the results are a tie. But Mallahan has a small edge with a 64.3% probability of winning; McGinn has a 35.7% probability of winning.

The distribution of election outcomes from the simulation says it better than numbers (see chart above).

The red bars on the left are Mallahan wins, and the blue bars on the right are McGinn wins.

There are a number of possible confounders here that make this extremely close race even more uncertain. Most obvious is the age discrepancy in support which The Stranger’s Eli Sanders points out may lead to some systematic (statistical) bias:

Remember, too, that SurveyUSA only reaches voters with land-lines, and that some of McGinn’s strongest support is among younger voters—who frequently only have cell phones.

Who knows….

Poll Analysis--King Co. Exec. Race:

The non-partisan King County executive race has proud Democrat Dow Constantine squaring off against bashful Republican non-partisan Susan Hutchison. Last week’s Washington Poll gave Constantine a 47% to 34% lead over Hutchison.

A new King-5/Survey USA poll released today essentially confirms last week’s findings. The poll of 614 likely or actual voters gives Constantine a 53% to 43% lead over Hutchison with 5% undecided.

As usual, I’ll use the poll numbers and sample size to assess the probability of each candidate winning (methods are given here). The Monte Carlo analysis of a million simulated elections gives Constantine 962,298 wins and Hutchison 35,378 wins. That is, the poll result provides evidence that Constantine will win Tuesday’s election with a 96.5% probability. Hutchison has a 3.5% probability of winning. Here is the distribution of outcomes from the simulated elections (see chart above).

The red bars are wins for Hutchison, and the blue bars are Constantine wins.

This is the first big test since last November’s initiative made the Executive a non-partisan position. And it sure looks like the electorate won’t be fooled by this non-partisan stuff.

Howie P.S.: As if things aren't complicated enough, here's "King County's Ballot Scanners can't handle close Mayor's race?"(Washblog).