At Corona Insights we never use opt-in panels for online survey research. (Opt-in panels are those where the members have sought out the panel and signed up to take surveys, usually in order to earn cash or rewards.) Many opt-in panels exist and they are widely used in some circles of market research (primarily because of their low cost), however, we have felt that the selection bias that can exist in opt-in panels poses too much risk to research quality. If the panel is made up of people who are in some ways systematically different than the population you need information about, the odds are good that you will get results from the panel that will mislead you about the population you are actually interested in.
So, we were very happy to see this article on ABCnews.com discussing the results of a recent study by Stanford University scientists (full report here), showing that, in fact, opt-in panels produce results that are significantly less accurate than results from randomly- (i.e., probabilistically-) selected panels. And perhaps even more important, weighting the results from the opt-in panel to match population demographics did not increase accuracy in the opt-in panel results.
In a sense, these results vindicate our commitment to using only proven, high-quality research methodologies, to ensure that our clients receive results they can trust – results they can rely on to make decisions.