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We were having an internal discussion regarding what specific signal Google is looking for regarding Site Speed. My understanding was that Google primarily used Time To First Byte (TTFB) as its signal of Site Speed. My colleague argued that this is not part of Google's PageSpeed Insights (https://developers.google.com/speed/pagespeed/insights/) and therefore was unlikely to be the primary signal. Who is right? Is TTFB the primary signal or the score on PageSpeed Insights?

One of our clients launched a new e-commerce site and there was a significant (60%) drop in traffic in Google Analytics following the launch. We are about 10 days into the new site, and our suspicion is that the move has caused a decrease in their site authority which has lowered their search position.

The old site had the store at sitename.com/store. The new site has a Shopify store at shop.sitename.com. There were very few external followed links to the store pages, so we thought that there would be little effect for overall site traffic by moving the store to a subdomain.

Any recommendations for next steps on diagnosing the problem and working towards a solution?

We were having an internal discussion regarding what specific signal Google is looking for regarding Site Speed. My understanding was that Google primarily used Time To First Byte (TTFB) as its signal of Site Speed. My colleague argued that this is not part of Google's PageSpeed Insights (https://developers.google.com/speed/pagespeed/insights/) and therefore was unlikely to be the primary signal. Who is right? Is TTFB the primary signal or the score on PageSpeed Insights?