A regular reader wrote recently to ask if we could compare the polls we have entered at this point in the current electorate cycle (2009 to 2010) to those we entered at this point two years ago. His concern is the possibility that Rasmussen Reports, the automated pollster whose results often show a house effect favoring Republicans, might be "flooding the zone" to a greater degree than in past elections. He pointed me to this post by Swing State Project diarist
blogger spiderdem, arguing that Rasmussen polls "have dominated the narratives in many of these  races as a result of their sheer frequency."
I've done a crude comparison that shows considerable apparent growth on the pace of polling so far this cycle -- though not just for Rasmussen -- but I need to caution readers about the limits of this data. Since races for Governor are far more numerous in a non-presidential years, I looked only at polls that tested U.S. Senate contests. In 2008, I counted up horserace results -- one per state -- for the general election match-ups that ultimately appeared on the November ballot. Unfortunately, we were only starting to enter polling data for non-presidential races at this point in 2008, so our internal database does not include many polls for potential match-ups that failed to materialize.
The problem, of course, is that we cannot predict which candidates will run and win primaries in 2010, so it is impossible to generate a strictly comparable list. Instead, I opted to count polls for this cycle for the candidate match-up in each state that has generated the most results to date. Also, I used wikipedia (sorry, Harry) to gather a few dozen polls in the less competitive contests that we are not yet charting here on Pollster.com.
The main point: my method is fuzzy. Others might come up with slightly different counts, and mine probably exaggerates the apparent increase in polling in the current cycle. Still, it should be close enough to give a sense for whether any one pollster is "flooding the zone."
On to the data. The following table shows my count of polls conducted at this point in each cycle. It shows a huge overall increase in polling on U.S. Senate races: 160 polls conducted as of last week as compared to just 74 at this point in 2008. Yes, Rasmussen has conducted more than three times as many polls fielding (45 vs. 13), but you can see similar rates of growth for PPP (21 vs. 5), Quinnipiac University (14 vs. 0), DailyKos/Research2000 (13 vs. 5) and several others.
Equally interesting is the decline for SurveyUSA, whose surveys are usually sponsored by local television stations. They had fielded 16 surveys on general election contests for U.S. Senate at this point in the 2008 cycle but none that I counted so far this time. Similarly, the number of polls conducted by less prolific media or non-partisan pollsters fell as a percentage of the total (from 26% to 16%), although the absolute number was slightly higher (26 vs. 19).
The message I get from these numbers is that the growth in polling in Senate contests so far this cycle has been driven by non-traditional media and academic sponsors and pollsters (like Rasmussen and PPP) that routinely conduct and release surveys without sponsors for their marketing value. These numbers also imply that traditional media sponsors -- local television stations and newspapers -- have cut back on their polling budgets over the last year.
But back to the question that prompted this exercise. Yes, Rasmussen Reports has fielded far more polls so far this cycle, both in absolute terms (45 vs. 13) and as a percentage of the total (28% vs 18%). One likely explanation is the "major growth capital investment" from a private equity firm they announced this past August:
"This investment will enable Rasmussen Reports to expand and enhance all aspects of our business," said Scott Rasmussen, founder and president of Rasmussen Reports. "That includes expanding our Premium Membership service and subscription base, developing new index products and sponsorship opportunities, and exploring new research techniques."
The more difficult questions, which my data do not answer, are those that critics have often asked about Rasmussen and that others will ask about PPP, Daily Kos and other pollsters or sponsors with a demonstrable point of view: Is bias or partisanship at work in decisions about where to poll, what to ask, and what population (adults, registered voters or likely voters) to interview?
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