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.
