FACTBOX: Iowa caucuses - small turnout, big impact

(Reuters) - Iowa's caucuses, an odd political ritual involving small groups of politically active citizens gathering in school gyms and living rooms, are the first formal step in selecting party candidates for the U.S. presidential election.

They have a big impact because they kick off the months-long drive to decide the two major candidates for president in November 2008 and they attract intense media attention.

Some facts:

-- The Iowa caucuses started modestly in 1972 as a way to spread out the nominating calendar and encourage more grass-roots participation. This time they are earlier than ever, on January 3.

-- The caucuses choose delegates to county conventions, the next step in a drawn-out process that ends in the spring with selection of state delegates to the national nominating conventions next summer.

-- On the evening of January 3, Iowans will gather in homes, schools and other public places. Republicans conduct a nonbinding straw vote to gauge individual candidate support to pick delegates. Democrats use various procedures including ballots or gathering in preference groups.

-- Relatively few Iowans take part -- fewer than 6 percent of eligible voters in 2004. Many tend to be older white people who represent the political extremes of their parties. Critics say the process is unrepresentative of the general voting population and given undue political weight.

-- While the caucuses have often been a springboard for future victories, other winners have later faded. George H.W. Bush in 1980 and Sen. Bob Dole in 1988 had big victories in Iowa but saw others pass them by for the nomination by winning later contests elsewhere. Both became the Republican nominee in later years.

-- The caucuses have mushroomed into a major event with media outlets from around the world converging on Iowa's snowy farmlands.

(To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at http:/blogs.reuters.com/category/events/trail08/)