What does "Delta" mean?

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

What is Delta?

The Greek letter delta is used to denote the difference between two parameters. The capital letter Δ is used when we speak of the difference in principle while the small letter δ is used when we refer to a particular realization after a test is completed.

The letter can be followed by some explanatory text, usually as subtext, denoting the type of difference (e.g. relative difference or absolute difference as well as, optionally, the variables for which it is computed.

Most of the time in A/B testing we are interested in reporting the differences between treatment and control, either as percent change or as absolute difference.

Related A/B Testing terms

Percent Change

Absolute Difference

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.

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