lways 0. An alternative is of course to then calculate the average of the <em>absolute</em> deviations. While this is a sensible measure of the spread of values, there are technical reasons to prefer the average squared deviation (i.e. the variance), which we won’t go into now. Let’s just plough on with how to calculate the variance. The variance of a collection of observed values, which is also referred to as the sample variance, is usually denoted as <span class="math inline">\(S^2_Y\)</span>, and de