From the beginning of the presidential campaign through last week, there had been 163 references in Nexis to Sen. Barack Obama (D-Ill.) being the most liberal Member of the Senate, with all of the news outlets relying on National Journal’s 2007 vote ratings (which, incidentally, placed New York Democratic Sen. Hillary Rodham Clinton at No. 16).

[IMGCAP(1)]To anyone who has spent more than a nanosecond around the Senate and has seen, met or watched Bernie Sanders (I-Vt.), Barbara Boxer (D-Calif.) or Russ Feingold (D-Wis.), among others, this rating is pretty ridiculous — as was the equally ballyhooed National Journal ranking of John Kerry (D-Mass.) as the most liberal Senator in 2004. All of this raises interesting questions about what it means to be liberal or conservative, and what these vote ratings, done by top-flight publications like National Journal and Congressional Quarterly, and by many interest groups, actually mean.

There has been some interesting and insightful writing by top political scientists about the National Journal claims regarding Kerry and Obama, most recently by the outstanding Congressional scholar Sarah Binder. (There was also a definitive analysis in 2004 by three political scientists from Princeton and Stanford universities.) There have also been good blog entries on the Obama rating by Michael Sherer and Steve Benen.

The first point to make is that National Journal’s ratings are an improvement over the previous static and unidimensional ones done by others, because they encompass three major policy areas: economics, foreign policy and social issues. But they have a huge basic flaw or gap — they are shaped dramatically by attendance and absences. There is only one reason that Kerry and Obama made the dubious distinction of most liberal (dubious because whether they are liberal or not, “most liberal” sounds extreme). It is because they missed a lot of votes while campaigning for president.

In his blog, Benen observed, “National Journal’s press release on the rankings noted the criteria were based on 99 key roll call votes last year: ‘Obama voted the liberal position on 65 of the 66 votes in which he participated, while Clinton voted the liberal position on 77 of 82 votes.’ So, Clinton voted for the liberal position 77 times, Obama voted for it 65 times, which makes Obama the chamber’s single most liberal member. Got it.”

To be sure, both Obama and Kerry would fit within the liberal camp; both would be in the top 20 in the Senate. But these rankings can’t really get any more precise than that. That is the second problem with vote ratings of this sort. As the political scientists Joshua Clinton, Simon Jackman and Doug Rivers pointed out in a political science journal, the ratings ignore ranges that reflect the gross imperfections of roll-call votes on the floor — many relying on shaky judgment calls to define “liberal” or “conservative” — that statisticians call “confidence intervals.” National Journal, like every other ratings operation, opts for false precision to have greater effect.

Sherer, in his blog for Time magazine, notes: “I actually browsed through the scorecard National Journal used to determine the rankings. There are precisely two scored votes where Obama took the more liberal position and Clinton took the conservative.”

Sherer goes on to say that the first was an amendment offered by Sen. Joe Lieberman (ID-Conn.) to establish a Senate Office of Public Integrity; Obama voted yes (along with Arizona Republican Sen. John McCain), while Clinton voted no. The second was an amendment Sen. Jeff Bingaman (D-N.M.) offered to the immigration bill on the renewal of non-immigrant visas; Obama voted yes, along with GOP Sens. Richard Shelby (Ala.) and Tom Coburn (Okla.), while Clinton voted no. Sherer says, “So there you have it. Obama is more liberal than Clinton because he voted with John McCain … and Tom Coburn.”

As Binder notes, the best ideological rankings are actually done by scholars Keith Poole and Howard Rosenthal, relying on all votes and a very complex method widely adopted by scholars. The Poole-Rosenthal scores make Obama the 10th most liberal Senator in 2007 — and, by the way, make McCain the seventh most conservative.

One larger point to make here. The flaws and limitations in the rankings have been systematically ignored by journalists writing or broadcasting on this issue — either because it gets too complicated or because the reality would spoil a good story, or in many cases, because reporters pick up the reference from one story and just repeat it in the next, and on and on. As a consequence, the assertions are exploited by political forces for their own purposes.

I don’t expect journalists to be statistical whizzes. But because these rankings have been flagged and analyzed repeatedly by reputable scholars and observers, I do expect some restraint in repeating the exaggerations. The problem is not simply National Journal’s — it is indeed, as most press accounts say, one of the best and most respected publications around. It is more the larger headache of journalistic sloth.

Norman Ornstein is a resident scholar at the American Enterprise Institute.