The sample variance is equal to 0 when all values in a data set are the same.
Variance measures how much the values in a dataset differ from the mean. When every value is identical, the mean will also be equal to that value. Therefore, there is no deviation of any values from the mean, which results in a variance of zero. In simple terms, no matter how many times you repeat the same value, there is no spread or variation among the values, leading to a calculation of variance that ultimately equals zero.