An Example of Margin of Error and Confidence Levels The key to the validity of any survey is randomness.

A confidence interval is a mathematical concept that expresses how likely a range will contain the mean of a data set.

In the most rigorous reporting of polls, you might see a sentence near the end that says something like “The margin of error is plus or minus 3 percentage points, at a 95% confidence interval.” ...

One quick note: Most polls report margins of error alongside another technical term, “ confidence interval.” In the most rigorous reporting of polls, you might see a sentence near the end that says ...

In the current election cycle, many media reports about polls are not including information about the margin of error.

Some of the better-known statistical rules of thumb that a smart consumer might think apply in polls are more nuanced than they seem. In other words, as is so often the case in life, it’s complicated.

An election poll's point estimate is stabbing for the right answer, but the margin of error usually includes the true figure. Sometimes even that can be wrong.

And since pollsters generally use a confidence interval of 95 percent, one out of 20 polls will be a statistical outlier – that is, outside the margin of error – just by chance.

Hold your breath and make sure you vote, because the result is likely to be a squeaker.