Filtering assignments by entry point
For some experiments, subjects are assigned to a variant in one place, but are not exposed to it until they perform a certain action. For example, users may be assigned to all experiments upon visiting the homepage of a website, but only a subset of those users navigate to a page where an experiment is being conducted. More examples of when to consider using an entry point are available in this guide.
Entry point for an experiment
Eppo provides the ability to filter an assignment source by an Entry Point (also known as a qualifying event) when configuring an experiment. This ensures that only the subjects assigned to that entry point are analyzed in the experiment, based on the logged events for that entry point. All decisions (inclusion into the experiment, time-framed metrics) are based on the timestamp of the entry point.
When you add an entry point filter, the entry point timestamp replaces the assignment timestamp as the start of each subject's analysis window. This means metric events are measured relative to when the subject triggered the entry point, not when they were originally assigned.
If you only want to filter which subjects are included (without shifting the analysis window), use an Assignment SQL filter or a targeting rule instead, or make sure the entry point and the assignment timestamps match.
The entry point entity must match the assignment entity for the join to work correctly.
First you’ll need both an assignment source and an entry point source configured. Then, when setting up an experiment, check the box marked “Filter assignments by entry points” in the Logging & Experiment Key section:
…and select the desired entry point:
The filtering will take place during the next experiment calculation (either during the scheduled time or a manual update).
Entry point for a sample size calculation
Before you run a test, we recommend that you check how sensitive that experiment can be using our Sample size calculator. Knowing how large an effect you can detect let you prioritize testing impactful, detectable changes. When the change will only be visible after the assignment, you can define an Entry Point to measure the sensitivity of the test more accurately.