Saturday, September 20, 2014

PolitiMath at PolitiFact New Hampshire

PolitiFact New Hampshire provides us an example of PolitiMath with its Sept. 19, 2014 rating of Sen. Jeanne Shaheen's ad attacking Republican challenger Scott Brown.

The ad claims Brown ranked first in receiving donations from "Wall Street," to the tune of $5.3 million.

PolitiFact New Hampshire pegged the reasonably "Wall Street" figure lower than $5.3 million:
Brown’s total haul from these six categories was about $4.2 million, or about one-fifth lower than what the ad said.
Note that national PolitiFact's Louis Jacobson, writing for PolitiFact New Hampshire, figures the difference between the two figures with the errant figure as the baseline. That method sends the message that Shaheen's ad was off on the number by about one-fifth, or in error by about 20 percent. Calculated properly, the figure in Shaheen's ad represents an exaggeration (that is, error) of 26 percent.

Curiously, PolitiFact doesn't bother reaching a conclusion on whether it's true that Brown ranks number one in terms of Wall Street giving. Jacobson says Brown led in four of the six categories he classified as Wall Street, but kept mum about where Brown ranked with the figures added up.

That makes it difficult to judge whether the 26 percent error implied by PolitiFact New Hampshire's $4.2 million figure accounts for the "Mostly True" rating all by itself.


For comparison, we have a rating of President Obama where the PolitiFact team made a similar mistake, calculating the error as a percentage of the errant number. In that case, Obama gave a figure that was off by 27 percent and received a rating of "Mostly True."


After a little searching we found a "Mostly True" rating of a conservative where the speaker used the wrong figure. Conservative pundit Bill Kristol said around 40 percent of union members voted for the Republican presidential candidate in 2008. The actual number was 37 percent. Kristol was off by about 8 percent. So "Mostly True."

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