Creating an experiment

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To create a new experiment, go to the A/B testing tab in the PostHog app, and click on the "New experiment" button in the top right.

This presents you with a form where you can complete the details of your new experiment:

How to create an experiment in PostHog

Here's a breakdown of each field in the form:

Feature flag key

Each experiment is backed by a feature flag. In your code, you use this feature flag key to check which experiment variant the user has been assigned to.

The feature flag will be created for you automatically. Therefore, you must add a feature flag key which does not exist yet.

Advanced: It's possible to create experiments without using PostHog's feature flags (for example, if you you're a different library for feature flags). For more info, read our docs on implementing experiments without feature flags

Experiment variants

By default, all experiments have a 'control' and 'test' variant. If you have more variants that you'd like to test, you can use this field to add more variants and run multivariant tests.

Participants are automatically split equally between variants. If you want assign specific users to a specific variant, you can set up manual overrides.

Participant type

The default is users, but if you've created groups, you can run group-targeted experiments. This will test how a change affects your product at a group-level by providing the same variant to every member of a group.

Participant targeting

By default, your experiment will target 100% of participants. If you want to target a more specific set of participants, or change the rollout percentage, you need to do this by changing the release conditions for the feature flag used by your experiment.

Below is a video showing how to navigate there:

Experiment goal

Setting your goal metric enables PostHog to calculate the impact of your experiment and if your results are statistically significant. You can select between a "trend" or "conversion funnel" goal.

You set the minimum acceptable improvement below. This combines historical data from your goal metric with your desired improvement rate to show a prediction for how long you need to run your experiment to see statistical significant results.

Note: If you select a server-side event, you may see a warning that no feature flag information can be detected with the event. To resolve this issue, see step 2 of adding your experiment code and how to submit feature flag information with your events.

Experiment goal warning


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Adding experiment code

Once you've created your experiment in PostHog, the next step is to add your code: Step 1: Fetch the feature flag In your experiment, each user is randomly assigned to a variant (usually either 'control' or 'test'). To check which variant a user has been assigned to, fetch the experiment feature flag. You can then customize their experience based on the value in the feature flag: Since feature flags are not supported yet in our Java, Rust, and Elixir SDKs, to run an experiment using these SDKs…

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