According to the Core Web Vitals section of the PageSpeed Insights documentation:
For aggregations with sufficient data in all three metrics, the aggregation passes the Core Web Vitals assessment if the 75th percentiles of all three metrics are Good. Otherwise, the aggregation does not pass the assessment. If the aggregation has insufficient data for FID, then it will pass the assessment if both the 75th percentiles of LCP and CLS are Good. If either LCP or CLS have insufficient data, the page or origin-level aggregation cannot be assessed.
Note that the documented behavior in Search Console's Core Web Vitals report is different:
A URL's status is the slowest status assigned to it for that device type. So:
- A URL on mobile with Poor FID but Needs improvement LCP is labeled Poor on mobile.
- A URL on mobile with Needs improvement LCP but Good FID is labeled Needs improvement on mobile.
- A URL on mobile with Good FID and CLS but no LCP data is considered Good on mobile.
- A URL with Good FID, LCP, and CLS on mobile and Needs improvement FID, LCP, and CLS on desktop is Good on mobile and Needs improvement on desktop.
If a URL has less than a threshold of data for a given metric, that metric is omitted from the report for that URL. A URL with data in only one metric is assigned the status of that metric. A URL without threshold data for either metric will not be on the report.
To summarize, PSI requires LCP and CLS data to make an assessment for a page or origin. Search Console will still assess a page group if any one metric has sufficient data. When there is sufficient data for a metric, the 75th percentile is always used for the assessment.