The Human Impact of Core Web Vitals

April 13, 2021 By: Trevor Pyle

Edd Saunders is an Optimisation Consultant and Core Web Vitals Specialist for one of our most trusted partners, LeanConvert


Google’s forthcoming Core Web Vitals update has left many in a frenzy. But the changes, which will launch in May, are actually a big step forward for site users and their experiences, and will (in theory) have a net positive impact on the web. (If you want to learn more about the basics, you can listen to LeanConvert’s podcast episode here). 

Until recently, people often overlooked the seemingly obvious connection between slow site speed and poor customer service–the exact connection that has Google reprioritizing. But this goes beyond SEO and algorithms; ultimately, this shift has very “human” benefits in regards to user experience. The new focus on Core Web Vitals is like prioritizing an express train rather than a local train. They might both go to the same place, but you know your travelers will be happier if they can get there faster. 

What’s the human impact of site speed? 

“Site speed can impact brand perceptions, customer experience, loyalty, and so on,” says LeanConvert’s Client Services Director Stuart Nelson. “Google’s shift in May is really just putting a name to something that has already mattered since the dawn of the Internet, thus making it a higher priority.” 

Slow websites damage the customer experience because our type 1 brains (or “Lizard brains” as psychologist and economist Daniel Kahneman referred to them) haven’t yet caught up with the rapid evolution of technology. We are, after all, only humans. 

This isn’t new research. The Neilson group performed a study back in the ‘90s that looked at the impact that slow loading might have on a user’s motivation to carry out an online task. The results highlighted that our feelings towards technology revolve around two points: 

    • Our desire to feel in control. 

Feeling in control breeds a sense of confidence and happiness in most people. In pre-civilized times, being in control of your environment and actions was critical to survival. When we request a website to load a page for us, we start to feel like we’re not in control, especially if we’re forced to wait for the site to accomplish what we’re telling it to do. This long-standing desire to be in control is what creates feelings of frustration, distrust, and unhappiness–albeit on a subconscious level–when a website isn’t responding instantly.

    • Our desire to process the actions we take. 

If an action happens in less than 100ms, our brain will process it as instantaneous. If the same action takes 1 second, we will interpret this wait as the machine responding to our inputs and processing the action. 

In order to quantify the above, Google has chosen to measure user experience using these new metrics: Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift. 

Why were these metrics chosen? 

Largest Contentful Paint: According to User and Customer Experience expert Joe Natoli, a key principle of UI design is dominance.

The viewer is drawn to the ‘dominating’ element of a site and uses that as their starting point, and their subsequent journey through the page is also directed from that point. A page without a dominant element means users might struggle to find their own starting point, making them work harder and conflicting with their hardwired desire to conserve energy.

It’s important that the LCP image loads quickly on a page to give users an authoritative starting point to navigating the website. You always want to reduce the users’ cognitive load. 

First Input Delay. According to PageSpeed Insights, your First Input Delay should happen within 0.1 seconds in order to be classified as “good.” This is calculated to be the minimum time it takes for our brains to feel in control of the outcome of an action. When we click a button and a website doesn’t process the action in .1s or less, we don’t feel like we’re directly controlling the “machine.” This brings about the feelings of distrust we mentioned earlier.

Cumulative Layout Shift. If you’re in a shop and the display starts moving about, you’re going to assume an earthquake is occurring. Whilst not on the same level, your subconscious is not going to feel in control of the environment if sudden changes take place on a website. Let’s revisit one of the critical thresholds – 100ms. If it takes our brain 0.1s to process an action, and elements on your page are shifting around, we’re increasing the cognitive load your visitor is experiencing as they’re trying to interpret the page.

Why is it a matter of UX, not just SEO? 

The May Core Web Vitals update being rolled out by Google has caused a stir in the SEO space. However, the importance of these metrics goes beyond any potential search engine ranking fluctuations. Optimising your site for the perception of quick loading, responsiveness, and stability will improve the experience your users will have while browsing your website, fostering brand loyalty. 

“It’s obvious to say that users prefer faster sites,” Stuart says. “Regardless of your SEO ranking, you could be losing or gaining millions of site visitors due to what are now being referred to as your Core Web Vitals scores.” 

Core Web Vitals is a major shift in how we view web performance. Rather than judging speed on a page-by-page basis, it looks to measure the customer journey throughout your website. 

We’ve known the importance of a swift and responsive website since the ‘90s, and businesses who are looking for a competitive edge have been optimising these factors for a long time.

Google recognizes that giving users the feeling of control will empower their customer journeys. The Core Web Vitals update is their way of making web performance mainstream.


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