Today was ACS day. As in the first release of 2011 data from the American Community Survey. There is a veritable unlimited number of topics that could be updated with the new data available and all the media folks chose to look at different topics. Locally it was the PG on poverty: Census data show poverty on rise in Allegheny County , and for the Trib it was commuting: Many more coming into city of Pittsburgh to work. Nationally and elsewhere it was a bunch of other topics with no one subject that was much more modal than the others.
I thought I would take a look at a factoid from the ACS that has been in the news locally in recent years: Biking in the City of Pittsburgh is up. You know, I agree, but the question is by how much has it increased and how fast is it increasing recentlySo before I start let me be clear that Pittsburgh has a long long history in biking and that I think the BikePittsburgh folks are great folks, do great things and the state of biking in Pittsburgh is far improved because of them. In fact Pittsburgh is gaining quite a Bike profile nationally likely as a result of their efforts.
So every year the larger League of American Bicyclists put out some decent benchmarking of biking in major cities. Last year there was a big factoid that came out of that showing a big increase in biking in the city of Pittsburgh. So what is the latest info on 2011? I won't steal their thunder with the national benchmarking, but for the City of Pittsburgh which is usually the focus here anyway.
Total using bicycle as a means of commuting to work for city of Pittsburgh from the ACS looks like this:
2009 - 1,9952010 - 2,2672011 - 1,894
So after a big jump between 2009 and 2010 there was a biggerdrop between 2010 and 2011?? Did biking all of a sudden become passé in the city of Pittsburgh?
Of course not! The data is not really even suggesting there was a drop in the last year, but at the same time there was likely not the jump the year before. So this is a near perfect foil to explain the dangers of overinterpreting American Community Survey data. Overinterpreting that much of the world is doing. My main message is that the ACS is best used to look at trends over time, but if you are really going to focus in on year over year changes you need to pay close attention. So on biking I went through this all last year: Grease inthe numbers, but I will update it all with the 2011 data. Below is a graphic of every comparable estimate of bicycle commuters in the city of Pittsburgh going back to 2007. I have not plotted the point estimates themselves, but the ranges including the margin of error the census reports for each data point. There are estimates for single years, estimates that are combined over 3 years and estimates that are an average over 5 years. When you look at the ranges you get a clearer picture of what ground truth is:
So what is the trend there? Up? I think it is up, but likely a more steady climb than what you might have thought by looking year over year. One last important note. The data here, like most bicycle usage data you see collected by the census is for 'commuting'. Commuting is by definition a mode of transportation to employment. If you use a bicycle for your primary transportation to school, shopping, recreation, or any other purposes it is not supposed to be reflected in this data. So in no way do these numbers reflect the full number of people who use bicycles each and every day. In fact I think the Bike Pittsburgh folks have collected their own data on the full spectrum of biking in town here and quite honestly I would trust those numbers more than the ACS estimates above.
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