[pmmucsd]

GCS regularly conducts validation surveys which measure the incidence rates of common health issues like asthma, smoking and disability along with consumption of various media to make sure it's sample is representative of the population. It's pretty accurate. You can read more about it here: http://www.google.com/insights/consumersurveys/static/consum...

[RobAley]

I've only skim read that as I'm at work, but it looks like it only compares their results with traditional internet surveys, is littered with caveats like it depending on the subject matter (type) of the survey, and doesn't fully show the methodology (full question wording and presentation, context, full details of respondents etc.).

It appears to only show the relative accuracy of certain types of questions in relation to other particular methods of internet surveys. Its not something that I would use to back significant spending decisions.