Gallup vs. Rasmussen: why the big difference?

Gallup and Rasmussen have a good track of election predicition accuracy recently.
But why the big discrepancy this year?

Gallup tells us that Hillary Clinton has a huge 19 pt. lead over Obama, while Rasmussen finds that the difference is only 5 points.
These latest primary polls (Gallup and Rasmussen) were both taken at the exact same time: April 2-5, in the case of the GOP primary, and a very similar timeframe on the Democratic side. Here is the summary:

Gallup (April 2-5): Clinton 38, Obama 19
Rasmussen (April 4-5): Clinton 34, Obama 29

Is one of these pollsters using a sample that is not representative of the voting population?

The GOP race is a similar story, with a remarkable difference between the two, but not as steep as in the Dem. race:

Gallup: (April 2-5) Giuliani leads McCain 38-16
Rasmussen (April 2-5): Giuliani leads McCain 27-16

To what do you attribute this difference?

accordingly

Did I miss something?

It was one of those "warning" threads. An, "uh oh guys, watch out for this in the future" type thing. I'm too poor to donate, so i can't search... :(

not literally owned by Repugs, but maybe a major contributor?

If it's true, I really want to know.

being bought right before the last election, but now I can't find it in a search, so I may be mistaken.

CEO Biography

Jim Clifton is best known in the polling and survey research field for leading the acquisition of The Gallup Organization in 1988, at which time he became CEO of the organization founded by the renowned polling pioneer, Dr. George H. Gallup.

Under Clifton's leadership, Gallup has enjoyed a tenfold increase in its billing volume and has expanded from a predominantly U.S.-based company to a global organization with 40 offices in 20 of the world's largest nations. The Gallup Organization is one of the world's largest think tanks and providers of public opinion polling and management consulting.

Clifton is best known in the business world as the creator of The Gallup Path. This metric-based economic model establishes the linkages between human nature in the workplace, customer engagement, and business outcomes. The Gallup Path is integral to the performance management systems in more than 500 companies worldwide and forms the basis of most of Gallup's total revenues.

Few people care as much as Jim Clifton does about what the world is thinking. His most recent innovation, the Gallup World Poll, is designed to tell the 10 million people who lead, govern, and manage the world what the world's 6 billion citizens are thinking. Clifton has pledged to continually collect people's opinions for 100 years in more than 100 countries to determine the general well-being or "soul" of a country, city, or culture. Questions in this ground-breaking project delve into individual and social needs, including food and shelter, safety and security, mental and physical health, education, jobs, economics and finances, transportation, water and air quality, hope and futurism, leadership approval, religion, and war and peace.

Clifton serves as Chairman of the Thurgood Marshall Scholarship Fund. He has received honorary degrees from a number of institutions, including a Doctor of Commerce degree from Bellevue University in Nebraska and Doctor of Humane Letters degrees from Medgar Evers College in New York and Jackson State University in Mississippi.

Clifton and his wife, Susan, live in Washington, D.C. They have three children, Nicole, Jonathan, and Jackie.

http://www.gallup.com/content/?ci=118

Is there some secret GOP code in here I'm not finding?

When I read this :


I get the distinct impression this is a Black man....Medgar Evers, Jackson State, Thurgood Marshall. Three of the four educational institutions listed are African American colleges or foundations, but he's a white guy.
http://www.mediabistro.com/articles/cache/a740.asp

Go figure....

named Herman Cain, whose right-wing credentials are:

-Syndicated Talk Radio Show Host, "The Herman Cain Show", FOX New Business Commentator and North Star Writers Syndicated Columnist

-Former Chairman and President of the (right-wing) Tax Leadership Council, the public educational component of Americans for Fair Taxation.

-At a nationally televised Presidential Town Hall Meeting on Health Care Reform (1994), challenged President Bill Clinton's health care proposal when he said, "Mr. President, with all due respect, your calculations are incorrect…"

http://www.hermancain.com/biography.asp

If a polling company decides to call at 3:00 p.m. and call only certain area codes (they understand the democraphics on something as detailed as the first 3 digits (after the area code) of a phone number and where those calls are being made), they will get an expected result.

Also, I have answered my phone before when a polling co. was calling, and they asked for the "Man of the House". When I told them that he wasn't there but I wanted to participate in the poll, they told me that they could only speak to a man.

This stuff is as done via actuaries.....just like insurance premiums.

It's all "managed" very well, thank you.

Gallup claims to be "random" in their polling yet I have friends who were asked by Gallup if they could be put on a list to be polled again. If Gallup is keeping a list, they could easily manipulate the outcome of any poll they're asked to do.

I've never worked for any of them, nor do I know anything about any of them. I would venture to guess, however, their credibility is their most valuable asset. I doubt they would spend it frivolously.

All of us know how questions can be framed to get a certain answer, or how one could expect a certain outcome by simply calling a certain geographic location. If someone is really interested in how pollsters collect their data,and thereby come to their conclusions, I'm sure the information is to be had. Look it up, request it, whatever needs to be done to get it and analyze it. All the answers as to why this poll came out this way and that one that way should be there. I bet there are even analyses done as to which pollster is more accurate at predicting such things as election outcomes more of the time. I'd look it up myself, but I can't think of a search term to plug into "the Google."

These two polls are not looking at the same population. The Rasmussen Republican primary poll is of likely Republican primary voters. The Gallup poll is of Republicans and Republican leaning independents. The Rasmussen Democratic primary poll is of likely Democratic primary voters. The Gallup poll is of Democrats and Democratic leaning independents. Since a fairly small fraction of the population votes in primaries, it shouldn't be too surprising that the results of the two polls differ considerably. I would guess that Clinton's bigger edge in the Gallup poll is largely a result of her higher name recognition as compared to Obama among the less politically conscious. Giuliani's smaller margin in the Rasmussen poll is probably attributable to the high representation of the religious right among Republican primary voters.

of elections, do you really believe rove would fail to gain control of polling?

Gallup used about 1,000 adults and Rasmussen used about 500 adults. That would lower the margin of error on the Gallup poll.

There is also likely to be some discrepancy in how the questions were asked. Gallup looks like they read off a list of candidates and asked for who you would "most likely" support. Rasmussen might have phrased the question differently, waited for people to volunteer an answer, polled on each major candidate, etc.

I don't pay for either polling service so I can't say for certain, but that would be my guess.