Margin of error describes the correctness of a survey. It tells, to what extent a particular survey is reliable. It is the measure of confidence level of the survey. Statisticians use a margin of error to define the uncertainty and accuracy associated with a particular survey or an experiment. More specifically, margin of error is an estimate that illustrates the accuracy of the sample.
It is defined as the measure of total amount by
which the results of a research are expected to vary from the actual
population. Margin of error is generally calculated as percentages, because most of the survey questions are answered in percentages.
Margin of error is expressed as:
Sample results (%) $\pm$ Margin of error (%) = Actual results (%) For example:
Let us consider that a survey was performed questioning people for their favorite leader for which they would like to vote in upcoming elections. Suppose that as the 32%
of the people that were sampled, say that they would like to vote mr. X
in upcoming elections. In order to project these results to the total population, researcher want to add a margin of error of 5%
to it. That means, 5% is added and
subtracted to the sample result in order to get margin of error that gives a possible range of results. i.e. it is to be said that-
Population varying from 32% - 5% = 27%
and 32% + 5% = 37%
would like to vote for Mr X. The actual results are supposed to lie between 27% and 37%.
In this way, the margin of error gives a range in which the actual results would lie and the researcher is confident enough that he is making a gap between the actual population and his sample taken.The margin of error is the measure of accuracy, It does not measure the amount of
bias that may be present in the data while sampling or surveying.