T scores are area-normalized scores standardized to have a mean of 50 and a standard deviation of 10. They are like normally distributed z scores except that they have been subjected to a linear transformation that changes the mean of the distribution from zero to 50 and changes the standard deviation from1.0 to 10. As a result, T scores are always positive, usually ranging from about 20 to 80, although more extreme values are possible. Ordinarily, T scores are reported without a decimal point; that is, they are rounded to whole numbers (48.4 becomes 48, 48.6 becomes 49).

T scores were first described by McCall and named in honor of three ...