A variance value of zero, though, indicates that all values within a set of numbers are identical. Every variance that isn't zero is a positive number. A variance cannot be negative. That's because it's mathematically impossible since you can't have a negative value resulting from a square.

Is the variance always 0?

By definition, the variance of X is the average value of (X−μX)2. Since (X−μX)2≥0, the variance is always larger than or equal to zero.

How is variance of constant is zero?

The variance of a constant is zero. ... Adding a constant value, c, to a random variable does not change the variance, because the expectation (mean) increases by the same amount. Rule 3. Multiplying a random variable by a constant increases the variance by the square of the constant.