Margin of error: what it means
A margin of error tells you how much a sample estimate may differ from the true population value. It is usually written as estimate ± margin of error. The important idea is that the margin gives a range of likely values around the estimate.
How to interpret it
- Identify the estimate and the margin of error.
- Form the interval by subtracting and adding the margin of error to the estimate.
- State the meaning in context: the true value is expected to be between the lower and upper bounds.
- If the question asks for a final simplified answer, write the interval in simplest form.
Example method
If an estimate is 50 with a margin of error of 3, the interval is:
- Lower bound: 50 - 3 = 47
- Upper bound: 50 + 3 = 53
So the interpretation is that the true value is likely between 47 and 53.
Check your answer
Make sure:
- you used both subtraction and addition,
- the interval is centered at the estimate,
- your wording matches the context of the problem.