Which of the following statements are correct?

The sample mean, regarded as a statistic (before a sample has been selected or an experiment carried out), is denoted by X-bar while the calculated value of this statistic is x-bar.

S²represents the sample standard deviation and is regarded as a statistic, while the calculated value of this statistic is s².

A statistic is any quantity whose value can be calculated from population data.

All of the above statements are correct.