What is the square root of the variance called?

The square root of the variance is called the standard deviation. Variance is a measure of how much values in a dataset differ from the mean, essentially quantifying the spread or dispersion of the data points. Standard deviation simplifies this concept by providing a measure that is in the same units as the original data, making it more interpretable and easier to understand.

When you take the square root of the variance, you convert the units back to those of the original data. This allows researchers and practitioners to understand the variability of their data in a more intuitive way. For instance, in educational assessments, if the standard deviation is low, it indicates that the scores are closely clustered around the mean, while a high standard deviation indicates a wider spread of scores.

The other choices do not pertain to this statistical measure; raw scores refer to the original data values without transformation, T-scores are standardized scores that indicate how far a value is from the mean in terms of standard deviation units, and percentile ranks measure the relative standing of a score within a distribution but do not express variability directly.