Margin of Error

What is margin of error?

A simplified definition of margin of error is the amount the results of a random sampling may differ from the results of surveying the whole.

In many cases, it doesn’t make sense (or it’s not possible) to survey an entire group, so a random sample is chosen instead. The margin of error states to what degree the sample results accurately represent the whole.

The smaller the margin of error, the more accurate the sample results are. The larger the margin of error, the less accurate the sample results may be.

What is a good margin of error?

A ‘good’ margin of error depends on the level of accuracy you need. While a 5% margin of error is fairly common, it can fall anywhere from 1% to 10%. Anything over 10% is not recommended.

The margin of error can typically be increased or decreased by adjusting the sample size of your survey.

Margin of error, confidence level, and confidence interval

Other closely related terms that might be mentioned in the context of margin of error is the ‘confidence level’ and ‘confidence interval’ of the survey. These terms are easy to get confused, so let’s break it down.

The confidence level is usually articulated as a percent - such as 95% - and states the degree of reliability for a randomized sample survey. It answers the question “how likely is it that I can repeat this survey and get the same results?”

The confidence level can range from 0% (zero confidence in the repeatability of the survey results) up to 100% (although it’s statistically impossible to ever be 100% confident). The higher the confidence level, the more reliable the survey results are.

The margin of error focuses on the range of possible error above or below the result of the survey.

The confidence interval is simply the maximum range of the margin of error. Since the margin of error can be above or below the survey results, the confidence interval is double the margin of error.

For example, if the result of a random sample shows 60% of customers are very satisfied with your service and you have a margin of error of 3%, you can expect that between 57% and 63% (confidence interval) of all your customers are very satisfied. The confidence level - for this example let’s say it’s 95% - tells you that 95% of the time you’ll get results that fall within 57-63% (confidence interval).

Additional resources for learning more about margin of error