What does "Theta" mean?

Definition of Theta in the context of A/B testing (online controlled experiments).

What is Theta?

The Greek small letter "theta" θ is usually used in statistics to denote an unknown parameter of interest. In A/B testing it is usually modeled as a random variable. The true value of θ is denoted θ*, while an estimator of theta, usually the maximum likelihood estimate is denoted with a hat above the letter.

The capital letter Θ is used to denote the parameter space: all possible values the variable can potentially take. It is also used with an index, e.g. Θ0 to denote the space under the null hypothesis and Θ1 to denote the space under the alternative hypothesis.

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.

Related A/B Testing terms

Minimum Effect of InterestEffect Size
Purchase Statistical Methods in Online A/B Testing

Statistical Methods in Online A/B Testing

Take your A/B testing program to the next level with the most comprehensive book on user testing statistics in e-commerce.

Learn more

Glossary index by letter

Select a letter to see all A/B testing terms starting with that letter or visit the Glossary homepage to see all.