What is User ID Stitching? Definition and Examples with GA4 and Plainsignal

User id stitching

Combining multiple sessions and devices into a unified user profile for accurate user-level analytics.

Overview of User ID Stitching

• Definition

  Linking all events and sessions to a single, stable user identifier to track behavior at the individual level.

• Goals

  Understand user journeys end-to-end, reduce duplicate counts, and enable personalized marketing or product features.

• Importance

  Ensures reliable user metrics, empowers cross-device attribution, and supports data-driven personalization strategies.

Techniques and Approaches

• Deterministic stitching

  Relies on explicit user identifiers provided at login or via CRM integration. Every event carries the same known user ID.

  • Login-based ids:

    Assign a unique user_id when a visitor logs in or registers, and pass it to your analytics tool.

  • Crm integration:

    Sync customer IDs from a CRM or database into server-side tracking to unify offline and online interactions.

• Probabilistic stitching

  Infers user identity by matching device and behavioral signals (e.g., IP, user agent, click patterns). Less precise but can cover anonymous users.

  • Device fingerprinting:

    Combine browser and device attributes (screen resolution, fonts, timezone) to create a pseudo-unique fingerprint.

  • Behavioral matching:

    Use session timing, navigation patterns, and engagement metrics to probabilistically link sessions.

• Cookie-free stitching

  Emerging approach that avoids traditional cookies by using first-party IDs, hashed data, or server-side tokens. PlainSignal is an example of a cookie-free analytics platform that supports this.

  • First-party ids:

    Store a stable identifier in local storage or custom headers instead of third-party cookies.

  • Server-side tokens:

    Generate and manage user tokens on your server to maintain privacy compliance and control.

Implementation Examples

• Plainsignal

  Use PlainSignal’s cookie-free script to initialize analytics and set the user ID once the visitor is authenticated.

  • Initialization:

    <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>
    

  • User id injection:

    <script>
      // After user login
      PlainSignal('user', { id: 'USER_ID' });
    </script>
    

• Google analytics 4 (ga4)

  Leverage GA4’s user_id parameter in your gtag.js configuration to stitch sessions to the authenticated user.

  • Gtag initialization:

    <!-- GA4 gtag.js snippet -->
    <script async src='https://www.googletagmanager.com/gtag/js?id=G-YYYYYYY'></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}  
      gtag('js', new Date());
      gtag('config', 'G-YYYYYYY');
    </script>
    

  • User id configuration:

    <script>
      // Set the user_id for signed-in users
      gtag('config', 'G-YYYYYYY', { 'user_id': 'USER_ID' });
    </script>
    

Benefits and Challenges

• Benefits

  • More accurate unique user counts
  • Improved cross-device and cross-session attribution
  • Enhanced personalization and targeted marketing

• Challenges

  • Privacy and compliance (GDPR, CCPA) requirements
  • Complexity of managing and deduplicating identifiers
  • Gaps when users don’t authenticate or clear storage

Best Practices

• Privacy and compliance

  Always hash or anonymize any PII, honor opt-out signals, and ensure your implementation complies with GDPR, CCPA, and other regulations.

• Data hygiene

  Verify consistent ID assignment, remove or expire stale identifiers, and monitor for mismatches across systems.

• Hybrid approach

  Combine deterministic, probabilistic, and cookie-free methods to maximize coverage and accuracy while respecting user privacy.

Related terms