My Largest Contentful Paint (LCP) data on Shopify Analytics looks great: 100% of visits with an LCP below 2500 milliseconds.
However when I run a test at PageSpeed Insights, the results for LCP are always between 5 and 12 seconds !!! and the performance score is between 53 and 65.
I wonder if this PageSpeed Insights score is the reason behind my low LP exp. score on Google Ads even though the actual real world data shows that my LP loading speed is great.
Can anyone explain the discrepancy?
What data would Google Ads rely on (specially in my case where my website is brand new and there isn’t enough data to have a CoreWeb Vitalis score assigned)?
This discrepancy is because you are comparing two different types of data: real user data versus a lab test. Your Shopify Analytics shows data from your actual visitors, who likely have fast connections.
PageSpeed Insights runs a simulated test on a slow network and mid-tier phone to find problems. Your site is fast for your current users, but the lab test shows it’s not well-optimized for visitors under average or poor conditions.
To answer your main question: for a new website, Google Ads uses its own lab test data similar to PageSpeed Insights, to determine your Landing Page Experience score.
It cannot see your Shopify Analytics data. The poor lab score from PageSpeed Insights is almost certainly the reason for your low score in Google Ads.
Do you think that, once my website traffic has some historical data Google will stop using lab test data in order to define my LP score? Or the lab test data will always affect my score on Google Ads?
Well, to be frank, not really. Once your site has historical data, Google Ads will start using that good real-world data, which will help your Landing Page Experience score. However, it will never completely stop using lab test data, so the lab score will always remain a factor.
The Google Ads system continuously uses its own automated crawl (a lab test) to get a real-time health check of your page. While a strong history of good real-user data will become a significant positive signal, a very poor lab score will always be a red flag to Google that your site is not well-optimized for users on slower connections.