Learn in the textbookDescriptive Statistics (Measures of Central Tendency and Dispersion)
DefinitionVariance (分散) is the average of the squared differences between each value and the mean, and it shows how widely the data are spread.
ExplanationA measure of dispersion is a number that shows how far the data scatter around their center. The difference between each value and the mean is its deviation, and because deviations simply added together cancel out to 0, they are squared before being averaged. If every value is the same, all deviations are 0, so the variance is 0 too.
AnalogyIt resembles scoring a round of darts by how far each dart lands from the center of the whole cluster of darts, with darts far from that center counting much more heavily.