Should you state a survey’s margin of error in your press release when pitching a story to the media? In our view, the answer is no. Why not? Because margins of error refer to sampling error only, not about the overall accuracy or error of the survey itself.
But how many readers of your news story understand what sampling error is? For that matter, how many researchers understand what sampling error is? It was only after four college semesters of advanced mathematical statistics that I finally “got it.” More importantly, how many readers understand that there are many other potential sources of survey error? Most undoubtedly assume that all error is somehow accounted for when you confidently proclaim the margin of error being ±4%. (Or, more absurdly, ±3.6% or even ±3.57% — examples of phony accuracy like this are all too easy to find.)
In short, margins of error are misleading because they deal with only one source of error. They convey a false sense of accuracy. And they should not be used. This idea is not always popular among colleagues and clients. But take comfort: One of the giants of public polling, Harris Interactive, refuses to report margins of error in its work, for precisely the reasons outlined above. Here we quote their methodological statement that accompanies every press release and report they issue:
All sample surveys and polls, whether or not they use probability sampling, are subject to multiple sources of error which are most often not possible to quantify or estimate, including sampling error, coverage error, error associated with nonresponse, error associated with question wording and response options, and post-survey weighting and adjustments. Therefore, Harris Interactive avoids the words “margin of error” as they are misleading. All that can be calculated are different possible sampling errors with different probabilities for pure, unweighted, random samples with 100% response rates. These are only theoretical because no published polls come close to this ideal.
We agree 100% with this statement, and advise our clients accordingly. In our view, the polling industry has an obligation to re-educate the media about this issue as well. Transparency requires that you (and we) report samples size, composition, and source. But transparency also requires a willingness to do away with misleading statements, no matter how much a reporter wants them.
—Joe Hopper, Ph.D.