Re: Plan for LCP data

Thanks for taking the feedback into account, I'm excited to see the
results! The plan sounds great.

I encourage you to release the full dataset whenever possible. For
synthetic data in particular (eg. SpeedIndex comparison) there should be no
privacy concerns, as those would be lab tests I presume. And whenever data
cannot be released due to user privacy, or has to be aggregated, a detailed
methodology would be very welcome.

On Wed, Oct 16, 2019 at 12:05 AM Nicolás Peña <> wrote:

> 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 Thursday, 17 October 2019 07:52:24 UTC