What does "Randomizer" mean?

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

What is a Randomizer?

A randomizer is any piece of software or hardware that can produce random numbers. Different requirements call for different types of randomizers: in some cases a pseudo-random number is enough, in others a true random number is a must. Generating a true random number is actually much harder than most people realize and over the years varying sources of randomness (entropy) have been sought with some including radioactive decay.

In online controlled experiments generating a pseudo-random number is usually enough since there are no security concerns and no one has an interest in predicting the next number in a sequence. Most software languages offer some kind of random number generating function and similarly most software providers that produce software which handles the assignment of users into treatment and control groups in an A/B test do so by using a randomizer. If you have an in-house system and randomize users yourself it is a good idea to generate at least 100,000 numbers from your randomizer and then it is advised to perform mis-specification tests for independence and normality to check for any departures.

Related A/B Testing terms

Randomization

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