The 90th percentile and Speed Scorecard

[joe....@mavens.co.uk]

The site speed metric on the new mobile Speed Scorecard shows the 90th percentile of First Contentful Paint from the CrUX report. It's always good practice to monitor the lower end of the user experience, rather than focus on averages. But can you explain the logic behind using the 90th percentile as opposed to 75th, 80th or other?

[Ellen Li]

We wanted to use a number that would capture the majority of user experiences for a given site. In this case, we went with the 90% best cases, as we believe this is more complete than averages or medians.