Dive Brief:

• Amazon was the top-ranked retailer — and second overall across all industries — on the Internet Retailer Mobile Performance Index for July, a program that monitors mobile website performance, while familiar sector names Groupon, Home Depot and Toys R Us also finished in the top 10, according to Digital Commerce 360.

• Walgreen’s fell out of the top 10 site performers in the index after holding the No. 1 overall ranking on the list for the month of June. The mobile websites for retailers on Internet Retailer’s Top 100 list averaged 99.48% availability from July 4-18 compared with 99.80% availability June 5-18.

• The index is compiled with data from Catchpoint Systems, which monitors webpage load time, availability, number of hosts and number of items per page. The measurements are taken from in-country or in-region monitoring nodes on major Internet backbones, at intervals of five minutes for two weeks each month.

Dive Insight:

Summer isn't the busiest shopping season by a long shot, but there is one big event smack dab in the middle of it: Amazon Prime Day. The fact that Amazon managed to keep up its mobile site performance during July, leading all other retailers despite its massive Amazon Prime Day event, is impressive.

During July, Amazon’s mobile site loaded, on average, in 1.31 seconds, slightly better than the 1.35 seconds measured by Catchpoint in June. Amazon's site traffic also visibly increased on Prime Day, July 11, by 49.1 compared to that same day the previous week. Somehow, the spike didn't drastically affect Amazon's average mobile site load time, even though the site's average number of hosts — 28 — and items — 98 — were higher than many sites that made the top 10.

Meanwhile, Walgreen's mobile website performance was down sharply during July, according to the index. From June to July, the average load time worsened from an impressive 0.82 seconds to a sluggish 2.98 seconds. Digital Commerce 360 stated that the slowdown resulted from an increase in the number of images and hosts, according to a Catchpoint spokesman.

Despite urgency to adopt personalization features and a number of other capabilities to make shopping on the web and on mobile easier and more satisfying, site performance remains an issue that can make both desktop, laptop and mobile smartphone shoppers head for the virtual exit door. New features and applications incorporated into sites can even sometimes be the problem, according to other recent research from Retail Systems Research and Yottaa.

Retailers want to do everything they can to attract mobile shoppers, but they also need to be sure that once those shoppers show up they have a quick and functional site to browse. That, in turn, means they probably should be testing and measuring on their own, as often as possible.