The importance of getting statistics right

The Atlantic picked up on an interesting piece of research from a demographer called Conor Sen from Atlanta:

The whole article is well worth a read. Something that sticks out however, is this claim:

But you may also be struck by the shape of that trend line (Sen is quick to note, by the way, that he’s not a statistician). It roughly suggests a political tipping point somewhere around a population density of about 800-1,000 people per square mile.

Justin Esarey, Assistant Professor of Political Science at Rice University, has picked up on it and noticed something  quite interesting.

As he notes:

Huh. Well, that did not look like a very good fit to me. So, I reconstructed the data set using the Wikipedia-sourced PVI data and the Census-sourced population density data that Conor talked about. I then ran an analysis of this data replicating Conor’s log-fitted model, plus a loess nonparametric fit line and a simple linear model. Here’s what these three models look like when plotted against one another:


What Justin is showing, is that by simply employing a different type of trend line you can paint a very different picture.

The interesting part (for me!) is how this would actually apply to political campaigns. For example, Dave Troy came to this conclusion using the original log fit line:

at about 800 people per square mile, people switch from voting primarily Republican to voting primarily Democratic

If you were to base a campaign on that principal, then depending on your voting system, it could be a fair assumption for a Democratic campaign to ignore districts with a population density of less than 800 people per square mile, and likewise, that very dense districts are only marginally more Democrat-leaning than moderately dense districts.

The two other trend lines tell a story. With them you get a far simpler, and in my view, far more logical story. Whereby there is no “tipping point” where a low population density district area becomes “worthless” to Democrats, and where a district continues to be stronger Democratic the higher the density.

All goes to show how important it is to get statistics right.

Please note: I am in now way claiming to be a professional statistician at all, so please excuse any errors on my part too!

Australian Labor leadership election

The ballot papers that rank-and-file members of the Australian Labor Party will receive this week are for the most important vote they will ever have as a member. For the first time, rank-and-file members will vote for the Federal Parliamentary Labor Party leader.

For a party that was often a pioneer amongst social democratic and labour parties, it seems odd that Australian Labor was the last major centre-left party in an English-speaking Westminster democracy to embrace the direct election of the leader.

A lot of that is due to the experience of the Australian Democrats, a socially liberal third party. The Democrats were a successful minor party for three decades, holding the balance of power in the Australian Senate and having representation in state parliaments. The party imploded after the membership of the party elected a federal leader that were not supported by the caucus room. The party now has no parliamentary representation and has been overtaken by the Greens. The Democrats have been cited by many opponents of the direct election of leader.

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NZ Election Ads

Two Dunedinites, James Meager and Ashley Murchison have recently launched a new website, NZ Election Ads, which “aims to create a repository of NZ election advertising for the benefit of researchers and voters alike.”

If you ask me this is well over due. They’re currently uploading lots of material from the 2013 local government campaign (I’m thinking about doing a best and worst post – there are some real shockers!) and will hopefully cover next year’s general election.

I’d highly recommend you check it out, and please upload anything you find.