We have already seen many of the reasons why surveys can be inaccurate, on top of the inevitable (and quantifiable) margin of error due to random variability. In this case the excess variability might be blamed on the sampling methods, in particular the use of telephone polls with a very low response rate, perhaps between 10% and 20%, and mainly using landlines. My personal, rather sceptical heuristic is that any quoted margin of error in a poll should be doubled to allow for systematic errors made in the polling.
Any quoted margin of error should be doubled as heuristic
