Variance
A measure of spread equal to the average squared deviation of values from the mean; its square root is the standard deviation.
Variance quantifies how much values in a dataset differ from their mean. It is calculated by averaging the squared deviations from the mean, dividing by n minus 1 for a sample. Squaring keeps positive and negative deviations from canceling out, but it also means variance is expressed in squared units, which is why the standard deviation is usually reported instead.
Variance is central to many analyses even when it is not reported directly. ANOVA partitions variance between and within groups, regression reports the proportion of variance explained, and homogeneity of variance is an assumption behind several common tests.
For thesis writers, understanding variance clarifies what your statistical tests are actually doing and why assumption checks belong in the methodology chapter. When an examiner asks how much of the outcome your model explains, the answer is a statement about variance.
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