Does PLT correlate with Speed Index

Analysis
1

Others have argued that PLT is a poor metric for web latency.

I was curious: how well do SpeedIndex values correlate with PLT values? The strength of their correlation would give us a sense of exactly how bad PLT is as a metric (assuming that SpeedIndex is what we really care about).

To answer my question I looked at the proportion of PLT to SpeedIndex (for mobile sites):

SELECT
  url,
  onLoad / SpeedIndex on_load_to_si
FROM
  httparchive:runs.2014_05_15_pages_mobile
WHERE
  onLoad IS NOT NULL
  AND SpeedIndex IS NOT NULL
ORDER BY
  on_load_to_si

And the result:

It looks like the correlation is pretty close for most sites. About 15% of the httparchive sites have a better SpeedIndex than PLT relative to the norm, and only a few percent of sites have relatively better PLTs.

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