Maybe We’re Not So “Courteous”: WSJ’s “Numbers Guy” Debunks That Driver Survey

Yesterday, I, and fellow Portland Metblogger jonashpdx, each blogged about that study that purports to show that we Portlanders are the most courteous drivers in the nation.

Today, though, The Wall Street Journal’s statistical methodology expert debunks the way in which the study was assembled, and findings crunched out.

Entitled “A Questionable Survey of “Road Rage,” this commentary was written by the WSJ’s widely respected “Numbers Guy,” whose own driver’s license reads Carl Bialik.

Read on for the most relevant excerpt:

“I asked Jennifer Ervin, an operations manager at Prince Market Research who worked on the survey, how respondents might know about driver behavior in other cities. She replied, “One might assume that they are basing their perceptions on reputations, general perceptions, news stories, and experiences and stories from friends and families.” AutoVantage spokesman Todd Smith said that many people experience other cities’ traffic because of work or personal travel: “We are an increasingly travel-oriented society.” He added that the survey was “national, comprehensive and scientific.”

“Regardless of whether the courtesy scores are a valid metric, they’re not exactly measurements of “road rage.” The survey did ask separate questions on whether people had engaged in aggressive behavior, such as responding to bad drivers with curses, obscene gestures or even by slamming into the back of another car (just 1% said they had done the last, though I’m not sure survey respondents can always be trusted to self-report bad behavior). But these results weren’t incorporated into the numbers used to rank cities. Interestingly, while Miami drivers were the most disapproving of their fellow motorists, they weren’t the quickest to react. They ranked in the bottom half of cities when it came to honking their horns at bad drivers. “As to ‘road rage’ vs. ‘driver courtesy,’ it may well be a matter of semantics,” Ms. Ervin told me.

“Inter-city comparisons of courtesy scores or horn-honking are problematic with this study, by the way, because the statistical margin of error for each city was plus or minus 10 percentage points. That means there’s not much difference, statistically speaking, between No. 9 San Diego (+7) and No. 19 Chicago (-13).

OK, PDX, are we still the most courteous?

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