When the Federal Do Not Call Registry was established in 2003 there was considerable speculation in the research industry around its likely impact on survey participation. Some people hoped that an overall reduction in calls going to registered households might increase the likelihood that people would start answering the phone again and agreeing to do surveys. There was a little bit of research on this but it was largely inconclusive. Western Wats did a phone study and concluded that survey cooperation would improve. I administered the same questionnaire to a Web study and was less sanguine about the future participation. But both studies seemed to say that people (1) didn't always understand what kind of calls were covered and (2) didn't make much of a distinction between telemarketing and research.
Now we have a good quality study of the real impact three years hence (Michael Link, Ali Mokdad, Dale Kulp, and Ashley Hyon, "Has the National Do Not Call Registry Helped or Hurt State-Level Response Rates?" Public Opinion Quarterly, 70, 794-809). The survey is the Behavioral Risk Factor Surveillance System (BRFSS), an ongoing federal study somewhat like our own PULSE study that interviews every month in all 50 states. The study looked at response rates by state for the period from January, 2002 through June, 2005. Their key measure was the correlation between the percentage of households in a state registered with the DNC and the monthly BRFSS response rate for that state.
Their conclusion is that the DNC has had no measurable affect. It has neither helped nor hurt survey participation. Response rates have continued to fall over the period they studied. They call for continued monitoring and express some hope that a reduction in unwanted telemarketing calls eventually will have an impact. But it's just that: a hope.