1) = The correlation between observed scores on parallel tests.

2) = The proportion of variance in X explained by a linear relation with X'.

3) = , the proportion of observed variance due to true score variance.

4) = , the squared correlation between observed scores and true scores, the shared variance between true and observed scores.

5) = , one minus the proportion of variance due to error.

6) = , one minus the squared correlation between observed and error scores.

An illustration of the amount of error in a test on the sampling distribution of one examinee's observed scores.

What is the standard deviation of this sampling distribution called in classical test theory?