Analytics platforms face a challenge: accurately tracking users across multiple devices and sessions. Without a user ID system, the same person visiting from a phone, laptop, and tablet gets counted as three separate users, skewing your data and obscuring the actual customer journey.
A user identifier or user ID is information that identifies a user and distinguishes them from others across multiple devices and sessions. When properly implemented, a unique user ID eliminates duplicate counting and attributes all activity to one person in your analytics reports, providing accurate visitor counts and complete customer journey data.
When user IDs become personal data under GDPR
User IDs create compliance obligations that organizations often underestimate. According to GDPR, any information that can lead to direct or indirect identification of an individual is considered personal data. This includes names, identification numbers, location data, and online identifiers like IP addresses or cookies.
If you’re collecting user IDs that can be linked back to individuals – which is often the purpose – you’re handling personal data and subject to full GDPR requirements. When you can connect a user ID to an email address, account number, or any other identifying information, you need proper consent, data processing agreements, and compliance infrastructure.
When to implement user IDs
Consider user IDs if: You need to understand cross-device behavior, have authenticated users (logged-in experiences), or need to connect analytics data to your CRM or customer database. These scenarios typically justify the complexity and compliance requirements.
Skip user IDs if: You’re tracking anonymous browsing behavior, don’t have user authentication, or your business model doesn’t require connecting sessions to specific individuals. Simple cookie-based analytics may suffice.
Exercise caution if: You operate in healthcare, finance, or other regulated industries where tying identifiers to individuals requires additional safeguards like encryption, access controls, and audit trails. The compliance burden increases significantly in these contexts.
More details about the user ID on the Piwik PRO help center and blog:
