## What is a t Score?

A t Score or a t-statistic is the result of applying a T-test and it represents a point from a Student's T-distribution with n-k degrees of freedom where n is the total sample size and k is the number of test groups in an A/B test. A t score is often not communicated directly but is first transformed into a p-value by calculating the cumulative distribution function of the relevant T-distribution.

A t score is rarely used in A/B testing since it is only needed when the population standard deviation is unknown and the sample size is smaller than 30. In all other cases the z score and the t score[/t] are identical for most practical purposes.

Like this glossary entry? For an in-depth and comprehensive reading on A/B testing stats, check out the book "Statistical Methods in Online A/B Testing" by the author of this glossary, Georgi Georgiev.