Registered democrats who are considered to be "likely caucus goers" in Iowa have been harassed by numerous canvassers, campaign calls, robocalls, polling calls, for months and months. It got so bad one guy emailed pollster.com to beg them to stop calling. He was getting 20 calls a day. It's not hard to imagine many of these people saying enough is enough and refusing to answer any of their phone calls, while the pollsters end up having more success with independents who have received less attention and are more likely to talk to the pollsters.
http://www.pollster.com/blogs/please_stop_calling_this_custo.php"Please Stop Calling This Customer"
Washington Post polling director Jon Cohen reported an easily overlooked but important statistic yesterday, especially to anyone thinking about the reliability of the last round of Iowa polls. Using the Iowa tables here at pollster.com, he determined that public polls in Iowa this year have interviewed nearly 80,000 "likely caucus goer" respondents:
As a ratio of voters polled to expected turnout, this must be something of a record. (In 2004 about 120,000 people participated in the Democratic caucuses, and in 2000 about 90,000 in the GOP contest.)
And it's not just the public pollsters calling. Campaigns have been known to set up a phone bank or two to gauge opinion, solicit support and cajole voters to actually show up and spend hours caucusing in the middle of winter.
A month-and-a-half ago, already deep into the "silly season" but well before the final stretch, eight in 10 likely Democratic caucus goers and nearly six in 10 on the GOP side said they'd been called on the telephone by at least one of the campaigns. And Pew reported the pervasive use of robo-calls (though most Iowans who get such automated calls about the campaign said they usually hang up).