Like all polling firms, Rasmussen Reports weights its data to reflect the population at large. Among other targets, Rasmussen Reports weights data by political party affiliation using a dynamic weighting process (see methodology).

Generally, our baseline targets are established based upon survey interviews with a sample of adults nationwide completed during the preceding three months (a total of 45,000 interviews). Targets have been updated monthly.

However, from now through Election Day, we are making two adjustments to that process. First, due to potentially changes in the political environment, we will now base our targets upon survey interviews conducted over the preceding six weeks, rather than three months. Second, we will update the targets weekly, rather than monthly. Each weekly update will be reported here.

At the moment, this shift will have little impact on the daily Presidential Tracking Poll. However, it could provide a significantly more reliable measure of the race as Election Day draws near.

During Election 2006, there was a notable shift in partisan identification favoring Democrats as Election Day approached. During Election 2004, there was a notable shift in the opposite direction. It is impossible to know which direction this will flow during 2008 (see month-by-month results). These shifts correctly foretold the election outcome in both years.

For polling data released during the week of September 14-20, 2008, the new targets are 38.7% Democratic, 33.6% Republican, and 27.7% unaffiliated. For the first thirteen days of September, the targets were 39.7% Democrat, 32.1% Republican, and 28.2% unaffiliated. It should be noted that these figures indicate an improvement for Democrats since the beginning of the year.

The new targets are fairly similar to the ratio that existed when Democrats won control of Congress in 2006. They are also fairly close to the make-up of the electorate in the Presidential elections of 2000 and 1996.

The current targets also suggest a significantly better environment for Democrats than they faced in Election 2004. When President Bush was re-elected, there were far more Republicans and far fewer independent voters.

In terms of immediate impact on the tracking poll results, a one-percentage point increase in the number of Republicans would typically lead to a little less than half-a-percentage point increase in support for John McCain. That’s because McCain has a roughly 80 percentage point lead among Republicans but is essentially even among unaffiliated voters. A one-percentage point decrease in the number of Democrats would half the same impact.