Comments on: Interpreting the polls: Likely versus registered voter surveys

By: Matthew Dickinson

Matthew Dickinson — Sat, 20 Sep 2008 13:13:38 +0000

George – Whenever pollsters conduct a telephone survey, they have a protocol they use to compensate for potential nonresponse bias, including any produced by people who screen their phone calls using caller i.d. In general, the non-response rate for telephone surveys – whether due to the use of cell phones, screening calls with caller i.d., the use of answering machines, has gone up in the last two decades, so that today up to 40% of calls get a “non-response”. This makes finding a truly random sample more difficult especially if that non-response is not randomly distributed, but instead falls within a particular demographic. Pollsters are aware of this, and do have a protocol for dealing with it. In the best case scenario, then, nonresponse bias shouldn’t affect survey outcomes, although it surely has made surveying more difficult.

By: Conor Shaw

Conor Shaw — Wed, 17 Sep 2008 22:29:17 +0000

For anyone who wants more evidence of the difference between polls of registered voters and polls of likely voters, look no further than the most recent news from Virginia at

http://www.realclearpolitics.com/epolls/2008/president/va/virginia_mccain_vs_obama-551.html

Wednesday’s CNN poll of registered voters has McCain up by 9%. PPP (a Democratic pollster) has a different poll showing Obama leading McCain by 2% in a poll of likely voters. Similar differences appear in the last set of polls in the state.

Interestingly, the VA polls actually indicate the opposite trend to the one Professor Dickinson mentioned in his blog about national polls. In Virginia, Obama actually seems to be polling better among likely voters than among the larger category of registered voters. I don’t have time to check the relationship of polls in every state but a quick glance at New Mexico’s polls shows that Dickinson’s theory holds in that state (I think it holds in most, actually)
http://www.realclearpolitics.com/epolls/2008/president/nm/new_mexico_mccain_vs_obama-448.html

Nonetheless, the example of Virginia may be an interesting one to consider. I’ll try to think of something that might explain what’s going on there, but I’d definitely be interested in your thoughts!

By: Gordon

Gordon — Wed, 17 Sep 2008 16:41:41 +0000

What about ‘caller id’ based differences…

I for one have it and do not answer calls that I do not recognize as being from someone I know – As such wondeirng what are the demographics for caller id subscribers…