Third-party content could be slowing Britain’s retail websites

Third-party content, such as advertising, testing and remarketing services, is having a detrimental impact on the load speed of some of Britain’s retail websites, new research suggests.


NCC Group’s website performance experts looked at the UK’s top 50 retail sites, then analysed the ten fastest and ten slowest. They found that on average, the slowest home pages contained 7.5 times more third-party content than the fastest. The faster sites averaged just 83KB of third-party content, while the slowest contained a staggering 618KB. To put this in perspective, the overall size of the smallest page tested was just 299KB.


The proportion of third-party content was also higher on the slower pages – 15 per cent of total page size, compared with just 9 per cent on the faster sites – suggesting that this content may be causing the webpages to slow down.


To get a realistic picture of each website’s performance, NCC Group used a custom metric known as Speed Index, which looks at how fast a web page is displayed, instead of measuring page load times. Ben Daniel, head of NCC Group’s web performance professional services team, explained:


“When it comes to the impact of third-party content on a website’s performance, page load times can be misleading. It doesn’t necessarily matter to the end user if the overall load time is slow if third-party services are loaded after the page has displayed.


“This is why we decided to use Speed Index. Our results show a clear correlation between the volume of third-party content on a page and the visual experience that page delivers to users. Third-party content wasn’t the only thing holding back the performance of the slower pages. However, we did see several cases of third-party content delaying the point at which pages started to appear.”


A number of websites used third-party scripts to test different versions of their site, and in one case this led to a six second delay before any content was shown on the screen.


Daniel continued: “Retailers can get a lot of value from third-party services such as A/B testing. However, when those services interfere with how their website displays, that value is severely diminished as slow web pages tend to deliver poorer conversion rates and can significantly impact the bottom line. However, when a testing process slows the web page down, it also introduces another factor that could compromise the results of that test. In other words, some retailers could be slowing their websites down for no reason whatsoever.”


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