Gallup is now mixing sampling methods to skew the results. Via Red State:

But now on July 19 that Democrats are showing a big lead, despite the fact that Gallup’s pretty graph now is titled Candidate Preferences in 2010 Congressional Elections, Among Registered Voters, the sampling is different:

Results are based on telephone interviews conducted as part of Gallup Daily tracking July 12-18, 2010, with a random sample of 1,535 adults, aged 18 and older, living in all 50 U.S. states and the District of Columbia, selected using random-digit-dial sampling.

Catch the difference? The Republicans lead with a sample of Registered Voters, but the Democrats lead with a sample of Adults. Someone who trusted Gallup’s pretty, but lying, picture would never have noticed. Real Clear Politics noticed, and actually recorded the polls differently. Friends noticed this and alerted me.

It is terribly dishonest for Gallup to string together two different polls as one series, as Gallup does not only in their graphs, but in their write-ups as well. Here’s an example from the July 19 release:

The Democrats’ six-point advantage in Gallup Daily interviewing from July 12-18 represents the first statistically significant lead for that party’s candidates since Gallup began weekly tracking of this measure in March.

Notice, they call the series one measure, even though it’s at least two different kinds of polls with two different kinds of sampling pools. You cannot pretend that a poll of all adults and a poll filtered by registered voters are part of the same series, even if the same questions are asked. That’s Polling 101, and whoever’s responsible for the Gallup release should have known this, and certainly whoever’s responsible for oversight of the Gallup releases would know this.

Reading this lends more weight to the entire JurnoList scandal.