(CNN) - So what are Tuesday's Iowa caucus-goers like – and how do they compare to the rest of the U.S. population?
Here's a thumbnail profile, by the numbers.
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For starters, they are not a big group. In 2008, about 119,000 people voted in Iowa's Republican caucuses - which is about the same as the population of Allentown, PA.
The biggest difference between caucus-goers and the rest of the country might be in ethnicity. In the 2008 caucuses, CNN exit polls showed that 99% of GOP caucus-goers were white, with less than one percent of any other ethnicity. In the nation as a whole, by contrast, 64% of the population is white, 16% is Hispanic, and 13% is black.
When it comes to religion, GOP caucus voters are more likely to be evangelical or born again. In the most recent CNN/TIME/ORC polling, 51% of likely Republican caucus-goers said they would call themselves evangelical or born again. For the general population nationwide, that figure was 38%.
"Maybe it's not reflective of the country as a whole," says Carol Hunter, political editor at the Des Moines Register. "But reflective of conservative Republican activists? I think they are."
Another difference between Iowans and the rest of the country: their state is in better shape economically. The unemployment rate nationally is 8.6%, but in Iowa it is only 5.7%.
And lastly, caucus participants are more rural: in 2008, only 12% said they live in a city of over 50,000, 19% said they live in the suburbs, and 69% answered "small city/rural."
–CNN's Keating Holland contributed to this report.