Plan for LCP data

Hi all,

At TPAC, some concerns were raised about the usefulness and the heuristics
of the LargestContentfulPaint (LCP) metric and publically available data
was requested to better evaluate the metric. Here is a summary of the main
points and what we intend to work on. Let us know what you think!

   1. LCP excludes background images of the <body>. There were concerns
   about this heuristic being arbitrary. To address this, we will present
   sample filmstrips where LCP is different due to removal of background
   images of the <body>.
   2. There was a request to look at how LCP correlates with ‘user
   happiness’ and business metrics. Chrome does not have a plan to obtain
   'user happiness' and none of our metrics intend to measure this. We could
   try to correlate LCP with engagement metrics, but the correlation might not
   be there: if all you want is to get some information quickly, a fast LCP
   might make your interaction with the page faster, but that's not
   necessarily bad. We'll be looking into correlation with business metrics.
   3. Chrome has not shown that LCP is a reasonable metric by correlating
   with known ‘good’ metrics, such as SpeedIndex. We will do a correlation
   study of LCP with SpeedIndex, FCP, onload, and maybe others. We should
   expect correlation primarily with SpeedIndex, but it would be interesting
   to look at correlation with the other metrics. Perhaps LCP can be viewed as
   a RUM alternative for SpeedIndex.
   4. Chrome has not shown that LCP is a necessary metric (i.e. not
   redundant, given the metrics developers could compute nowadays). The
   correlation study can help shine some light into this. If there is not a
   good correlation between LCP and other metrics that can be measured in the
   wild, then that’s a good signal of independence. In addition, we can show
   examples where LCP differs from the page load metrics that are easy to
   compute in the wild today (FCP, onload, any others we should include?).
   These examples would highlight LCP as an ‘independent’ metric: one that
   cannot be easily estimated by using the other load metrics available today.

Received on Tuesday, 15 October 2019 22:05:03 UTC