PageSpeed Insights and Google Search Console data have different use cases — understand the differences between field data and lab data
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.
CWV fluctuations are common, even if you’ve not made changes to the page
One user notes seeing a lot of fluctuation in their Core Web Vitals (CWV) metrics, despite not making any changes to the pages themselves. Core Web Vitals metrics depend a lot on field data, which is collected from real users accessing your site. Users browsing from different locations and with different device/connection types can be the cause of these fluctuations, as each experience is unique.
Core Web Vitals metrics are weighted toward the pages with the most traffic on your site
Google’s Core Web Vitals (CWV) metrics are typically looked at through a sample of traffic to the overall website. Therefore, it’s the pages on your site that get the most visits that will contribute the most to the overall CWV score. Having pages on your site that perform poorly for Core Web Vitals, but don’t bring in a lot of traffic, is going to be less of a concern. In the same vein, pages with little traffic and great CWV metrics aren’t likely to pull up the site-wide score. The exception is if Google has enough data to segment a certain part of the site and treat it separately. For example, a super fast blog with lots of visits may end up being looked at on its own, away from the rest of the content on the site.
The desktop Page Experience roll-out is unlikely to cause immediate or significant ranking changes
As page experience rolls out as a ranking factor on desktop, John is keen to clarify that the weight it holds will largely mirror what’s seen on mobile. If it’s clear that a page is the best result for that query, page experience signals could be downplayed. If there are multiple pages in SERPs that could answer the user’s query and intent equally well, page experience is one of the factors that could be used to distinguish between them and rank one site above another.
Even significant speed improvements may only have a subtle impact on visibility
John warns users not to expect significant rises in visibility from speed improvements alone. This is true even if the speed goes from very slow to very fast in a short space of time. Given the complexity of Google’s algorithms, changes that affect page speed in isolation are likely to have a much more subtle impact on visibility.
SEO improvements based on CWV metrics take about a month to show results
Google’s Core Web Vitals look at data that is delayed by around 28 days. This means that any significant page speed improvements you make on your website will typically take about a month to show up in the search results.
Core Web Vitals are weighted equally across all industries and website types
Neither the type of website nor industry vertical will alter how much weight is given to Google’s Core Web Vitals metrics.