What is “margin of error”? We see this term used in surveys and political polls quite often. What does it mean and how is it obtained? Whose error?

From a book often used in the Herald-Leader newsroom titled Numbers in the Newsroom:

Most organizations cannot survey an entire population, so they “sample” part of the population. Margin of error, also called sampling error, is a method for telling the reader how likely the poll results are correct. An example: A 2.5% margin of error means the the poll results will report answers within a 5 % point range. So, “error ” refers to the possibility of error within the survey. A detailed explanation of this involves statistics, formulas, confidence intervals, more. It’s important to know that margin of error is made up of three elements:

1. The number of people in the survey (the more people surveyed, the smaller the margin of error)
2. The differences in the answers (there’s a smaller margin of error when 90% respond one way than when 55% respond that way)
3. How accurate the pollster wants the answers to be

A simple way of understanding the concept: the smaller the margin of error, the more likely the results are correct.

The Denver Post has an interesting article on the current state of political polling.

Filed under: Election