- Using one or two data points to determine a "trend," and
- Using an arbitrary "starting year" as a point of comparison.
The chart in the article shows that ridership has been falling for one year, based on just one data point (Later in a Tweet, Nelson told me she had two data points, with ridership down in both calendar 2014 and ’15, but that’s not in the article or the chart.)
|Los Angeles Times|
Based on these one or two points, the authors propose a vast and ominous trend:
The Los Angeles County Metropolitan Transportation Authority, the region’s largest carrier, lost more than 10% of its boardings from 2006 to 2015, a decline that appears to be accelerating. Despite a $9-billion investment in new light rail and subway lines, Metro now has fewer boardings than it did three decades ago, when buses were the county’s only transit option.Accelerating? You need many data points to support this claim, because you are saying not just which way the line is going but also how it’s curving. What the published chart shows is that:
There’s a larger interesting story about the broad fall in ridership across the 90s and dramatic recovery across the 00s.
Ridership has been generally flat since 2006, going up and down in about a 10% band, with no sign of strong movement in any direction.
When a journalist says some grand thing has been happening since year y, you should immediately ask: “why year y in particular?” Again, here’s how the article opens:Indeed, you can create any story about ridership you want simply by choosing a "starting year" on the graph above: "This “arbitrary starting year” trick is a very common in misleading journalism. Be suspicious whenever you see a single past year is cited as a point of comparison."
For almost a decade, transit ridership has declined across Southern California despite enormous and costly efforts by top transportation officials to entice people out of their cars and onto buses and trains.Why “almost a decade”? Why not just a decade? Because if you compared 2015 to 2005 instead of 2006, ridership wouldn’t be down, and the authors wouldn’t have a story.
Sure, ridership is down 10% since 2006. But it’s up since 2011 and way up since 2004. Want to talk about the grand sweep of history? Nelson says that ridership is lower than it was 30 years ago, which sounds terrible, but it’s higher than it was 25 years ago!
I completely understand the pressure for journalists to create a neat "story" that will generate all-important page views; as a commenter on Walker's blog says, "part of the problem with journalism is that you want to have a snappy headline. 'Transit Ridership Goes up and Down' won’t do it." However, journalists do a disservice when they use tricks such as the ones Walker identifies to exaggerate, or even fabricate, stories such as these. This is especially true of something as politically polarizing and as poorly understood as public transportation. Maybe it's another reason why journalism should come with warning labels.
In a second post, Walker takes issue with the same LA Times article for its apparent assumption that short-term ridership is the only worthwhile measurement of a transit system's success. In a third post, Walker picks apart a post by anti-transit extremist Randal O'Toole regarding LA's ridership decline; anybody who wants to understand why I, as a transportation planning professional, have very little respect or use for O'Toole and his screeds should read it.