Think Polls Are Biased Towards Democrats? Then Check Out This Chart

On Monday, we wrote about how the new site UnskewedPolls manipulates data in order to produce the message they want. 

Here, we have the chart that shows why they’re doing this all wrong. 

Basically, what UnskewedPolls does is take a poll and look at the partisan percentage split that the poll reports from the random sample. This could be, for instance, a 33 per cent Democrat, 28 per cent Republican, and 39 per cent independent breakdown.

Then, they somehow weight the data so that what comes out is what the sample would look like if the Democrat/Republican/Independent percentages were equal to the results found by Rasmussen Reports in the single month of August— 35.4 per cent Republican, 34 per cent Democrat, and 30.5 per cent Independent. 

The resulting number comes out overwhelmingly favourable for Mitt Romney. 

Using figures from Talking Points Memo’s excellent polling database, we looked at 60 polls from the past two years that surveyed what the partisan split of the United States was. 

These polls found an average of 32.2 per cent Democrats and 24.4 per cent Republicans taken as a whole. 

We plotted the partisan split of each poll here. You’ll observe that there are two polls which seem to disagree with the data — one is a Bloomberg Poll from this past week, the other is an New York Times/CBS poll from October 2011.

The red plot point is the Rasmussen Reports poll that has formed the basis for the analysis. You’ll observe that it disagrees substantially from a two-year record of a statistically significant  number of polls. 

poll party identification split

Photo: Walter Hickey/BI, Data from TPM PollTracker

Essentially, the source of the partisan split for the shift is substantially different from the consensus area.

Were to use an aggregation of Rasmussen Party Identification polls they could make a compelling argument perhaps, but cherry picking a single favourable dataset to coordinate your analysis is poor form. 

For now — or at least until the group can justify its analysis — UnskewedPolls is suspect at best. 

Now, learn everything you need to know about how to understand a poll >

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