Skip to main content

Subjects

Introduction​

When calling Eppo's SDK to get assignments, you'll need to provide a subjectKey. This key represents a unique identifier for the entity being targeted and/or experimented on (e.g., a user). When Eppo evaluates randomized targeting logic (experiment assignment, limited traffic exposure, etc.), this ID will be hashed and used to bucket subjects. That is, subsequent calls to get<Type>Assignment will always return the same variant for the same subjectKey, as long as targeting eligibility does not change.

For experiment analysis, subjectKey is also used to join assignment events to outcome events.

This page walks through several common choices for subjectKey and considerations for each.

Examples​

Authenticated users​

A simple example of an experiment subject is an authenticated user, typically identified with a userId. In this case, simply pass that value in as the subjectKey. Downstream analysis should be simple: just add other tables from your data warehouse that also track userId. There's no need to instrument new events specifically for Eppo.

Unauthenticated users​

It's common to run experiments before a persistent userId has been created. For instance, any pre-authentication traffic on your site that does not yet have an associated userId. Fortunately there are several options for what to use as a subjectKey in this case.

Common solutions include storing an identifier in localStorage, accessing device-level identifiers, or leveraging a consistent identifier from a managed analytics platform like Segment, Amplitude, or Rudderstack.

For more details on each of these options, see our guide on choosing a subject key for pre-auth experiments.

Company (for B2B businesses)​

B2B companies may want to guarantee that users from the same company see a consistent experience. This is easily achieved by simplying passing companyId in as the subjectKey. Subsequent analysis can either use company-level data or user-level data via clustered experiment analysis.

No subject​

In cases where you want all traffic to see the same variant you can simply pass in a hardcoded value as the subjectKey. This may make sense for situations where you want to simply toggle a feature on or off for 100% of traffic.