Why Do CWV and PageSpeed Scores Differ? Google Answers.

3 min read

In an Office-hours Hangout recorded on 1 July, 2022 Google’s John Mueller discussed why scores of Search Console Core Web Vitals and PageSpeed insights tend to vary after a viewer asked him which of the two scores should one consider while assessing. John said that there is always a disparity between two measurements and why it is meant to be this way. The reason this is so because each of the two tools is designed to serve different purposes, but is often confused to serve a common purpose by the users. Where the Core Web Vitals report shows “real world usage data”, PageSpeed Insights shows you ways to improve your website’s speed across all devices.  So, should you consider only one of the two scores or both at merit? Let’s a deep dive into the whole discussion with John.

Core Web Vitals Report vs. PageSpeed Insights Scores

Here is what the viewer asked.

“When I check my PageSpeed Insight score on my website, I see a simple number. Why doesn’t this match what I see in Search Console in the Core Web Vitals report? Which one of these numbers is correct?”

Here’s what John said.

“I think maybe first of all, to get the obvious answer out the door, where is no correct number when it comes to speed, when it comes to understanding how your website is performing for your users.

In PageSpeed Insights, by default, I believe we show a single number that kind of is a score from 0 to 100, something like that, which is based on a number of assumptions, where we assume that different things are a little bit faster or slower for users. And based on that we calculate a score.

In Search Console we have the Core Web Vitals information which is based on three numbers for speed, responsiveness and interactivity. And these numbers are slightly different, of course, because it’s three numbers not just one number.”

The scores are derived differently and that is why they are different.

With CWV, it is kind of the like the scores are a reflection of how actual site visitors see while visiting a site. And Google determines this score on the basis of all the core web vitals data that the users have opted to share with Google via Chrome. On the other hand, PageSpeed Insights provides information that is either diagnostic in nature (as to how to improve page speed) or offers insights as to because of what metrics the site is performing well.

John continued.

“But also there’s a big difference in the way that these numbers are determined. Namely there’s a difference between so-called field data and the lab data. Field data is what users have actually seen when they go to your website. And this is what we use in Search Console.

That’s what we use for search as well. Whereas lab data is kind of a theoretical view of your website, like where our systems have certain assumptions where they think, well the average user is probably like this, using this kind of device and with this kind of a connection perhaps.

And based on those assumptions, we will estimate what those numbers might be for an average user. And obviously you can imagine those estimations will never be a hundred percent correct.”

Mueller on why CWV Data might not always be consistent.

“And similarly, the data that users have seen, that will change over time as well, where some users might have a really fast connection or a fast device and everything goes really fast on their website, or when they visit your website. And others might not have that. And because of that, this variation can always result in different numbers.

Our recommendation is generally to use the field data, the data you would see in Search Console, as a way of understanding what is kind of the current situation for a website. And then to use the lab data, namely the individual tests that you can run directly yourself, to optimize your website and try to improve things.

And when you are pretty happy with the lab data that you’re getting with your new version of your website, then over time you can collect the field data, which happens automatically and double-check that users actually see it as being faster or more responsive as well.

So in short, again, there is no absolutely correct number when it comes to any of these metrics. There is no kind of like absolutely correct answer where you’d say, this is what it should actually be. But rather, there are different assumptions and different ways of collecting data and each of these are subtly different.” concluded John.

Based on all the insights provided by John and the details mentioned on Google Support, it is evident that both the tools serve a different purpose and should be used accordingly. Watch John Mueller’s full response to question at the 31-second mark and may be also stick around for the rest of the discussion for some other valuable insights.

Source: Search Engine Journal