What is a User Identifier in Analytics? Examples in GA4 and Plainsignal

User identifier

A persistent string that uniquely identifies users across sessions and devices for comprehensive analytics.

Overview of User Identifiers

• Definition

  A User Identifier is a unique alphanumeric token assigned to track individual users across sessions and devices.

• Key purpose

  Enables user-centric metrics such as retention rate, lifetime value, and personalized user journeys.

Types of User Identifiers

• Authenticated identifiers

  Generated when users log in; tied to a user account for reliable cross-device tracking.

• Anonymous identifiers

  Stored client-side via cookies or localStorage; persists until cleared by the user.

• Client ids (ga4)

  GA4’s client_id is stored in a first-party cookie to identify devices over sessions.

• Cookie-free identifiers (plainsignal)

  PlainSignal uses a fingerprint-based ID that works without cookies, ideal for privacy-first tracking.

Implementing User Identifiers

• Ga4 integration

  Use the gtag or analytics.js API to set a custom user_id parameter after user authentication.

  • Ga4 code snippet:

    <script async src="https://www.googletagmanager.com/gtag/js?id=GA_MEASUREMENT_ID"></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}
      gtag('js', new Date());
      gtag('config', 'GA_MEASUREMENT_ID', {
        'user_id': 'USER_ID_VALUE'
      });
    </script>
    

• Plainsignal integration

  Embed the PlainSignal script to enable cookie-free user tracking out of the box.

  • Plainsignal snippet:

    <link rel="preconnect" href="//eu.plainsignal.com/" crossorigin />
    <script defer data-do="yourwebsitedomain.com" data-id="0GQV1xmtzQQ" data-api="//eu.plainsignal.com" src="//cdn.plainsignal.com/PlainSignal-min.js"></script>
    

Benefits and Challenges

• Benefits

  Key advantages include:

  • Cross-session analysis:

    Understand user behavior over multiple visits and devices.

  • Accurate attribution:

    Improve conversion tracking by linking actions to the same user.

  • Personalization:

    Deliver tailored content based on known user preferences.

• Challenges

  Potential issues include:

  • Privacy compliance:

    Ensure user IDs comply with GDPR, CCPA, and consent requirements.

  • Data fragmentation:

    Different IDs across systems can lead to duplicate or incomplete profiles.

  • Implementation complexity:

    Synchronizing IDs between client and server adds development overhead.

Best Practices

• Use stable identifiers

  Prefer authenticated user IDs over ephemeral tokens to maintain consistency.

• Merge anonymous and authenticated ids

  Link sessions upon login to unify user history.

• Hash or anonymize ids

  Protect user privacy by hashing or pseudonymizing identifiers.

• Document id flows

  Maintain clear documentation on how and when IDs are assigned and synchronized.

Related terms