By Bob Benenson, CQ Staff

House race scorecard advisory: As is the case every two years, all 435 House seats are up for election in 2008. The Democrats currently hold 236 seats to 199 for the Republicans.

The handicapping of all of the nation's Senate, House and gubernatorial contests has been a staple of Congressional Quarterly's election coverage for more than a half century, and it naturally has reached many thousands more readers since 2006, when the launch of the free CQ Politics site expanded our reach nationwide and well beyond our traditional audience within the Washington political community.

CQ invented the ratings system — which many other analysts and news organizations came to adopt and adapt to their own styles— in the early 1950s. Originally a product of the Congressional Quarterly Weekly Report, now CQ Weekly, the ratings evolved into seven categories:

Safe Democratic: The Democratic nominee is/will be a strong favorite, and an upset is virtually impossible.

Democratic Favored: The Democratic nominee has/will have a strong lead and appears likely to win, but an upset cannot be completely ruled out.

Leans Democratic: The Democratic nominee has/will have an edge, but the contest appears competitive and an upset is a live possibility.

No Clear Favorite: Neither party has established a definite lead in the contest (the rating is equivalent to “tossup”).

Leans Republican: The Republican nominee has/will have an edge, but the contest appears competitive and an upset is a live possibility.

Republican Favored: The Republican nominee has/will have a strong lead and appears likely to win, but an upset cannot be completely ruled out.

Safe Republican: The Republican nominee is/will be a strong favorite, and an upset is virtually impossible.

One point that needs to be clearly understood is that the contests rated "Leans," as well as those rated "No Clear Favorite," are very competitive and could go either way — and so it behooves those with partisan rooting interests to pay close attention and make no presumptions about those contests' outcomes.

The slightly favored candidate in a Leans race has something going for him or her that we believe justifies the rating: years of popular incumbency, their party's strong track record in the state's or district's election, a big edge in campaign fundraising or other advantages. But the challenger also has qualities that makes her or him a highly viable contender. If that weren't the case, the race would be rated in the "Favored" category for less competitive races, or the "Safe" category for non-competitive races.

We have for years tried to apply a mental framework in designating these ratings. No Clear Favorite races are those we believe will end up the closest, with the winner prevailing by a razor-thin margin. Leans races are those we think, in greatest likelihood, will end up with a winner taking between 51 percent and 54 percent. Favored races are those we think could end up with a winner taking roughly 55 percent to 59 percent. And most Safe races should end up with the victor taking 60 percent of the vote or more, a landslide in our books.

But even these are just guidelines. There are cases in which we might think a race might be fairly close if the election were held today, but have strong reasons to believe that the contest will end up as much more or much less competitive by November, and our rating will reflect that sense.

How we come to these conclusions involves a combination of factors. We look at the candidates' political experiences, electoral track records (if they've run for office before), personal biographies and campaign skills.

While the candidate with the most funds does not always win, money matters in campaigns, so we mine information from the contenders' finance reports.

We apply our knowledge of the states' and districts' partisan voting habits and the demographics of their political constituencies. And we listen closely to the party and state organizations about which contests they are most heavily targeting, which also is reflected in their own spending strategies.

Oh, did I forget to mention polls? I'd best not, because much of the criticism we get from folks who disagree with a rating is often prefaced with the statement, "I just saw a poll..." Yes, of course, we read the polls on the races, but they are not the sole or even predominant factor in our ratings. Without getting into the many vagaries of political polling there are many circumstances in which competing polling firms produce drastically different results on the same contest, and in which an individual company's surveys will change significantly from one survey to the next, and then sometimes swing back in the other direction. Our goal here is to give you our best estimate of how a race is going to turn out, and not to make you dizzy by changing our rating every time the latest poll comes in.

Don't even get me started on "own" polls, those conducted for candidates' campaign and political parties. Many of the firms conducting these surveys are highly reputable, but that doesn't mean that the polls done for Democrats and the polls done for Republicans in the same race don't often differ drastically. If the Democrats say their poll shows their candidate winning by 10 percentage points and the Republicans say their poll shows their own candidate winning by 10 percentage points, there are only two possibilities: either one of them is way off base, or they both are, with the real number magically somewhere near the mid-point of the two partisan polls.

We are very cognizant of the heightened sense of urgency that the 24/7 news world created by online communications. But it does make me chuckle a bit, as someone who started at this political prognostication business back in the more laid-back days of print-only journalism. Right into the mid-1990s, CQ would publish and make changes in its ratings only three or four times during an election year, in election supplements published by the Weekly magazine. Our ability today, on CQ Politics, to make ratings chances on virtually any day and at any hour is lightning fast by comparison.