An an increase in hosts, items on its page plus several URL redirect links have caused Neiman Marcus Group’s neimanmarcus.com mobile site homepage to slow down in the first quarter, according to digital performance analytics company Catchpoint Systems Inc.

URL redirection, which is also called URL forwarding, is when a shopper visits one URL in a web browser and a page with a different URL opens. This is used to shorten a URL, prevent broken links when a retailer moves a web page or to allow multiple domain names that belong to the same owner to refer to a single website, according to Catchpoint. These redirects, plus an increase in the number of  hosts, including third-party services, items and a large site overall, caused Neiman Marcus’ mobile site to progressively slow down throughout the quarter, according to Catchpoint. Neiman Marcus did not respond to a request for comment to explain why it is redirecting more of its mobile URLs.

NeimanMarcus.com’s mobile site loaded in 3.19 seconds on average on mobile devices Jan. 1-March 31, which is nearly a second slower when measurements began in early January, when it loaded in 2.25 seconds on mobile, according to data from Catchpoint.

Still, NeimanMarcus.com loaded faster than the Mobile Performance Index average, which was 3.32 seconds. Catchpoint monitors Internet Retailer’s Top 100 online retailers for site speed on both desktop and mobile devices.

And when looking at other mobile site speeds from top online retailers, Gamestop.com shed more than a second from its mobile site load time to 2.81 seconds on average in the first quarter from 3.94 seconds last fall. This was mostly due to reducing the images on its homepage, says a Catchpoint spokesman.

Overstock.com also had a notable mobile speed performance for increasing its overall page size without causing its mobile site to slow down. In fact, Overstock.com’s mobile site loaded in 1.96 seconds on average in the quarter, compared with 2.79 seconds last fall. Previously, a few of Overstock.com’s hosts, or domains that deliver content, caused bottlenecks to its page load time, but have been improved this quarter, according to Catchpoint.

Here are the top speeds on mobile among Internet Retailer’s Top 100 online retailers:

For desktop speed, W.W. Grainger Inc. and Sears Holdings Corp. operate a few of the fastest desktop sites this quarter, with Sears.com loading in 0.96 seconds and Grainger.com loading in 1.29 seconds. By comparison, on average, Internet Retailer’s Top 100 retailers loaded in 3.47 seconds on desktops.

Both of these retailers use the same tactic to ensure a speedy load time, according to Catchpoint. Both retailers arrange their slowest-loading elements, such as JavaScript, to load last, so the visitor can start interacting with the page immediately and not have to wait for a heavy item to load.

“Sears takes special steps to reduce the potential negative performance impact of having so many hosts and items,” a Catchpoint spokesman says. “[Sears] does this by loading critical elements early in the page-load process so that the page becomes interactive faster; the user can scroll through the page and ‘interact’ with the page.”

Here are the top speeds on desktop among Internet Retailer’s Top 100 online retailers:

Catchpoint monitors each website’s homepage with measurements taken from Catchpoint’s in-country or in-region monitoring nodes. Backbone monitoring nodes are the locations of Catchpoint’s devices that are near data centers operated by the main internet service providers that provide service to a city. The nodes simulate end-user contact with each website. Catchpoint monitors webpage load time, availability, hosts and items.

They are defined as follows:

Webpage load time: The time it takes for enough page elements to load for a consumer to begin interacting with a page, such as searching, tapping or scrolling. From a consumer’s point of view, this is the time it takes for the progress bar or spinning wheel to stop.

Availability: The percentage of time during the two-week test period that the site can be successfully reached by a consumer.

Host: Any domain that delivers data, content or services over the internet to the site.

Items or Requests: Web page components, such as files or images that a page loads from internal and external hosts or domains. These can include PDFs, PNGs, JPEGs and GIFs.

Neiman Marcus is No. 43 Internet Retailer 2018 Top 1000, GameStop is No. 40, Overstock.com is No. 32, Sears is No. 24 and W.W. Grainger is No. 10.