A user asked about the difference between PageSpeed Insights (PSI) scores and the CrUX (Chrome User Experience Report) data found in Google Search Console (GSC). According to John, ultimately there’s no ‘correct’ number to use when it comes to speed and performance assessments — both PSI and GSC data can be used for different things.
The PageSpeed Insights score calculates a simplified overall score based on a number of assumptions about your website’s speed and the average user. Google Search Console, on the other hand, uses Core Web Vitals data and a sample of actual visitor experiences relating to speed, responsiveness, and interactivity.
John points out that there’s a difference between “field data” — numbers based on what real users have seen when they go to your website — and “lab data”, which is more of a theoretical view of your website, based on more generalized assumptions about the average user (with considerations for which devices most people will use, average internet speeds, etc.).
Both types of data are designed to give you insights into what users are experiencing or are likely to experience on your site.
John recommends using the field data in GSC to understand the current situation on your website and the lab data (namely individual tests you can run yourself) to optimize your site and try to improve things for the future. When you’re happy with the lab data you’re getting after making updates to your site, over time you will also automatically be collecting the field data in GSC. You can double-check the field data against the lab data to ensure that actual users are experiencing the improvements.
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