Website Optimisation - Implications of Lab vs Field Data

18 May 2022

Whether you look at lab data or field data to analyse your website's performance can make a big difference. 

Data from Google's Core Web Vitals (CWV) can measure your website's performance such as how fast your site loads specific parts, how it compares to other websites, how your page loading speed impacts user experience and page rankings, etc. 

Related Link: How to Optimise your Website's Speed

While Google uses field data for page rankings, looking at lab data to examine the performance of your website could be quite fruitful. By comparing these two, let’s show you how to optimise your site's performance in real-time. 


Lab Data 

Lab data can be used to assess your website’s performance under ideal conditions, using a fast computer and a high-speed internet connection close to the site's servers. Most  tools available online generally use lab data to determine page loading speed metrics. Lab performance data helps to reveal problems that slow the system down or other elements that prevent the page from loading as it should. 

However, it is possible that lab data might give you a false sense of security about your page loading speed because most users would not be accessing your website under ideal conditions. At the same time, you cannot ignore them as these are available on-demand (e.g. CruX data is released every month) and are easy to get and detailed.  


Field Data  

Field data is collected under real-world conditions, using computers of varying speeds (ages) and at different locations around the world. Field data can be filtered and simulated to see how your site performs under a specific set of conditions.  

This data is quite important in giving an accurate picture of how your site functions and ranks, although it takes longer to collect this information and even then, it can be difficult to pinpoint what the specific issues are. 


Collecting Field Data 

What matters for Google is how real users access your site, use it to get information or shop for products. In this case, field data is more reliable than lab data, revealing problems with your website that lab data might not show to help you improve your page rankings. However, lab data can provide the details of the metrics you need to solve the issue. 

Google’s Core Web Vitals (CWV) are extremely helpful for collecting field  data.  

The main Core Web Vitals metrics include: 

  • Largest Contentful Paint (LCP) measures overall loading performance 
  • First Input Delay (FID) the soonest a user can interact with the site 
  • Cumulative Layout Shift (CLS) measures page stability and how often it changes 

Previously, CWV only used lab data and Google had strict limits on page loading speeds in these areas. Now they take into account both field and lab data when calculating page loading speeds.  


The CrUX of the Matter 

For a pure field experience report, Google offers CrUX – the Chrome User Experience Report – that provides valuable data from millions of Chrome users. The CrUX report includes information about website performance metrics such as: 

  • First Paint
  • First Contentful Paint
  • DOMContentLoaded
  • First Input Delay
  • Largest Contentful Paint
  • Cumulative Layout Shift
  • Time to First Byte
  • Notification Permissions
  • Effective Connection Type
  • Device Type
  • Country 

This exhaustive list should help you to see your site’s  strengths and weaknesses clearly and as you optimise, the CrUX report can verify how much improvement there has been over time.  

CrUX data can only be accessed using specific tools or an API, but there are plenty of free options available. PageSpeed Insights API and Google PageSpeed Insights are two easy-to-navigate options to review field data and apply it to your SEO-enhancing efforts. 

There are other powerful tools you can use for deeper analysis and insights, such as Google Search Console, Google Data Studio Dashboard, Google BigQuery, and CrUX API. However, these tools do require some professional understanding for proper use. This is where Enlighten Designs’ Web Health Check would be able to help you. 


Using the Data 

When you just want to know how your site functions in a controlled, ideal environment, lab data will be more helpful. For example, if you need to debug your site or make improvements to optimise it, lab data will give better information because, under the same conditions, you will get very similar results. This will give you a point of comparison as you make changes to the site and show you where problems are lingering. As in-depth lab data can be easy to get, you can dive into details to debug the issues.  

On the other hand, field data can tell you how your website performs in the real world – on everything from the best and fastest modern systems to older systems that struggle to deliver good performance. By collecting and testing field data about your website’s perfomance, you can significantly reduce the risk of running into major problems as well as planning to fix them. The data provided by Google’s Core Web Vitals can not only show you real-world data about your site but can also replicate how your site will perform under a given set of conditions. 

For example, Vodaphone did an A/B field test on a landing page using Core Web Vitals to see whether optimisation made a difference. Their field data showed that when they improved their LCP by 31%, it led to an 8% jump in sales and a 15% increase in lead to visit rates.  

Similarly, Pfizer found out that 15 of their sites for 40 different brands were loading slowly, including one site that took 21 seconds to load. By requiring sites to use images and code that loaded under lab conditions within a certain number of seconds, Pfizer was able to improve their loading time by 38% and reduce their bounce rate on those 15 sites by 20%. Pfizer’s efforts used a combination of lab and field data to achieve their results.  


Why it all Matters 

Staying on top of your website performance is essential to being visible to your customers when they are looking for your products or services.Contact us today to see how we can provide the services you need.