# Holdout groups: Advanced use cases

This article helps you:

• Best manage experiments with multiple holdout groups

• Rollout experiments with holdout groups and mutual exclusion

This article reviews advanced use cases you may run into while using holdout groups in Amplitude Experiment.

## Case 1: Streamline multiple experiments and holdout groups

Adding an experiment to multiple holdout groups may limit an experiment's traffic. This is because each user must be evaluated for each holdout group they belong to.

For example, imagine two holdout groups:

• Holdout group 1: This group contains experiment A and experiment B, with a holdout percentage of 5%.
• Holdout group 2: The second group contains experiment A and experiment C, also with a holdout percentage of 5%.

Since experiment A is part of both holdout groups (1 and 2), it will receive the majority of the total traffic:

0.95 * 0.95 = 0.9025 (90.25%)

Instead of adding an experiment to multiple holdout groups, create a single group with all the relevant experiments instead. This will allow for a more even distribution of traffic across experiments.

In the example above, you would create just one holdout group containing all three experiments (A, B, and C).

## Case 2: Handle experiments with holdout groups and mutual exclusion

Adding an experiment to a holdout group and a mutual exclusion group can also further limit the amount of traffic to the experiment. Each user will be evaluated for both the holdout group and the mutual exclusion group.

For example, imagine the following holdout group and mutual exclusion group:

• The holdout group has a holdout percentage of 5% and contains experiment A.
• The mutual exclusion group has half the traffic directed to experiment A in slot 1, with the other half going to experiment B in slot 2.

In this scenario, experiment A receives about half of the total traffic:

0.95 * 0.5 = 0.475 (47.5%)

Using holdout groups with mutual exclusion isn't forbidden, but be cautious of the potential traffic limits as you plan and roll out your experiments.

Learn more in this article about mutual exclusion groups.

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April 25th, 2024

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