The margin of error is an estimate of a confidence interval for a given measurement, result, etc. and is frequently cited in statistics.
While phrases such as, "The poll has a margin of error of plus or minus 3.1 percentage points" are commonly heard, an additional qualification such as "at a 95 percent confidence level" is also needed in order to precisely indicate what the error refers to.
For a given confidence interval , standard deviation , and sample size , the margin of error (for a normal distribution) is
where is the inverse erf function.