PageSpeed Insights Lab Tests & Aggregate CrUX Report Data Are Used for Assessing Site Speed
Some of the sources that Google uses to assess site speed are PageSpeed Insights lab tests and aggregrate data from the Chrome User Experience Report.
Speed Metrics Important for UX Are Different to Metrics Important for Crawling & Indexing
While there is some overlap, speed metrics that are important for UX are completely different to those used for crawling and indexing. For the latter, Google needs to be able to request the HTML pages as quickly as possible and server response time is also important.
Use Lighthouse Metrics to Understand How Users Experience Site Rather Than Search Engine Algorithms
Google uses a variety of metrics to determine site speed, but a lot of the metrics in Lighthouse are more likely to impact how users judge speed rather than Google’s search algorithms. John recommends testing site speed with users rather than trying to determine if Google sees it as too slow.
Speed is a Minor Ranking Factor Compared to Content Quality or Relevance
Improving site speed alone probably won’t change rankings or visibility for a website because it is a very small factor compared to the relevance and quality of a page’s content with regards to rankings.
Lighthouse Analysis Uses Medium-end Smartphone on 3G Connection
Lighthouse analysis uses an average smartphone on a 3G connection to measure speed. This might account for discrepancies between Lighthouse and independent tests which might be carried out over a much faster Wi-Fi connection.
Server Location Shouldn’t Impact Google’s Page Speed Measurement
The geographic location of a web server shouldn’t impact Google’s measurement of page speed. They have labs data to artificially measure the speed a page would take, and field data to measure the speed of pages for real users.
Google Speed Tool Scores Don’t Map One-to-one with How Speed is Used for Rankings
The scores shown in Google’s page speed tools such as PageSpeed Insights don’t map one-to-one with how sites will be ranked in search in relation to their speed.
Lab Data & Field Data Differ in New PSI Tool as User Devices Differ From Google Default
The lab data can differ from the field data in the new PageSpeed Insights tool because users sometimes have different devices than the default device that Google would use for testing.
Web.dev is Built on the Lighthouse Infrastructure in the Back-end
Google’s web.dev tool is built on Lighthouse in the back-end to maintain consistency with other tools.