the point really is not its too close to call and just gave a representative sample.
Texas is giving the pollsters particular headaches not because they don't know what groups support who but because they cannot figure out who is going to vote. Texas and Ohio take whatever poll you want to follow - the pollsters are not confident and their own commentary is interesting
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The demographic mix is especially important in Texas given the large percentages of both African American and Latino voters there. Fortunately, in this case at least, we now have a fairly complete look at how these polls of "likely Democratic primary voters" differ demographically. When the data was not already in the public domain, I received quick cooperation (in Texas) from the pollsters at Washington Post/ABC News, Constituent Dynamics, Hamilton Campaigns and Public Policy Polling (PPP). Also, an encouraging number of pollsters have included demographic profile data their Texas releases, including several that are typically more reticent, including ARG, Rasmussen Reports. And thanks to the Houston Chronicle, even the Zogby/Reuters/C-SPAN poll helped make the world a "better place" by making cross-tabs featuring demographic composition available on Chron.com.
Even though the following table includes results for just four pollsters, the range of adults represented** is huge, from a low of 7-8% for the Texas Credit Union League(TCUL)/Hamilton Campaigns/Public Opinion Strategies poll to a high of 40% on the first poll from SurveyUSA. The TCUL poll obviously comes closest to past turnout, although turnouts have been much higher in other states so far this year than in 2004. The ABC News release concedes that an actual turnout of 24% of adults is "unlikely" but reports that "vote preference results are similar in likely voter models positing much lower turnout
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The real results from the pollsters - because of the unique aspects of this race they do not know who is going to vote.