A simple rule of thumb is that, if you are estimating the percentage of people who prefer, say, coffee to tea for breakfast, and you ask a random sample from a population, then your margin of error (in %) is at most plus or minus 100 divided by the square root of the sample size.2 So for a survey of 1,000 people (the industry standard), the margin of error is generally quoted as ± 3%:
