Tuesday, February 16, 2010
A Call for Standards on Wikipedia
An example of why this firsthand information should be used was demonstrated in a post about Evan Bayh's retirement on Monday by one of the coolest kids on the block Mr. Nate Silver. The post compares something known as the Cook Partisan Voting Index (used for measuring how Democratic or Republican a state or Congressional District is compared to the country as a whole) to DW-Nominate scores (measuring how conservative or liberal a Congressman's or Senator's voting record is). Silver was basically trying to show that Bayh is more liberal than one would expect Indianan (or Hoosier) Senator would be.
In the post, Silver shows his tendency, like many others, to cite Wikipedia almost obsessively. In the article I linked to, four out of the five cites are from Wikipedia. I am sure most of the information in these articles is accurate, but one of the articles on the Cook Partisan Voter Index (CPVI or PVI) had one of the aforementioned warning flags at the top. In fact (see the video posted below), I could only find one link in the article on PVI. The page links to the House PVI rankings after the 2008 elections. Not surprisingly, the rankings for the House that appear on Wikipedia seem accurate.
But no link exists for the State PVI rankings, which is what Silver is utilizing. I was going to work on my own piece using the PVI index, so I decided to check the numbers that appeared on Wikipedia at the original source... And, it turns out, the Wikipedia page is inaccurate.
26 out of the 50 states have inaccurate PVI calculations. On average, the difference between the Wikipedia page's PVI and actual PVI is about .62 when you use Cook's website calculations to the tenths place and .64 when you only go out to the whole number. When going out to the whole number, 21 states differ by 1 point, 4 differ by 2 points, and 1 differs by 3 points. Note Silver's Indiana is at R+5, when in fact it should be at R+6 or 6.2.
Considering Silver's entire article is based upon PVI, these errors could definitely have an impact on his findings. I would re-run Silver's numbers, but I am a bit uncertain on how he came to them. His directions are a bit unclear. This post will be edited, if I or someone else (perhaps Silver himself) can figure out exactly what he did. I have, however, reproduced at the bottom of this page part of his graph showing the relationship between PVI and and DW-Nominate Scores.
Of course, the need to correct the post would not be necessary, if Silver had checked the firsthand source. Silver is certainly not the only one who links to Wikipedia (heck I have cited it once on this blog before). I am just using his post (because his blog is read by so many people) as an example of what can go awry when you do not check your sources.
I really hope we all would simply verify anything we find on Wikipedia. It is the right and academic thing to do. See for yourself how easy it is to make a citing Wikipedia error, and how easy it is to avoid.
The District of Columbia, not used in Silver's analysis, is not included in the tables, but its correct PVI of 40.7 in the Democratic direction is different from the 39 in the Democratic direction seen on Wikipedia.
To interpret the table and graph:
Negative PVI scores indicate a state that was more Democratic on average over the last two election cycles (2004 and 2008) than the country as a whole, while negative DW-Nominate Scores indicate a Senator with a more liberal voting record. One would expect Senators from Republican states to have higher DW-Nominate scores, while Senators from Democratic states to have lower DW-Nominate scores. Feel free to play around with the correct PVI data.
I have no problem going to wikipedia as a first resort (I do it). I just ask that the lists are verified.... That's all. As I said in the post below, I used it to get some Strategic Vision information...
Subscribe to Post Comments [Atom]
Subscribe to Posts [Atom]