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In statistics, variance is a measure of the spread of a set of data with respect to the average value, or mean. Mathematically speaking, variance is the sum of the squared difference between each data point and the mean -- all divided by the number of data points. More simply, variance means getting some results or data points that deviate from the average or expected result and representing that difference numerically. This can be an advantage, a disadvantage or both.

## Statistical Surveys

Finding variance in a survey data set is typically considered a good thing. It can be a sign that a survey was set up to correctly take a range of information from respondents. For example, a survey of yes-or-no questions may not provide much detail about the subject of the questionnaire. However, a survey on the same subject with respondents choosing from a range of answers offers more information -- and a greater chance of variance. Variance could be seen as a disadvantage only if the surveyor saw results that deviated from a desired outcome.