Consumers can’t shop on a mobile site they can’t access. Site availability is just one of the metrics mobile and web performance testing, monitoring and analytics firm Keynote measures in its weekly index—but it’s an important one. For the week ending Aug. 31, J.C. Penney improved its availability by 4 percentage points and leapt 11 spots in the rankings.

Peter Filias, mobile web expert at Keynote, calls that a staggering leap. “J.C. Penney did this by eliminating timeout errors,” he says. A timeout error occurs when an extended period of time passes without a server answering the call of a web browser, which eventually gives up. “Week over week, the frequency of these has been significantly reduced.”

But the site could use some help on load time, which increased more than a full second from 10.00 seconds to 11.09 seconds. “The J.C. Penney mobile home page gained seven elements and 19 kilobytes in size from the previous week, which brought the latest total element count to around 80 and total page size to over 500 kilobytes,” Filias says. “Although the page saw an increase in size and element count from the previous week, the merchant still saw a large move up in ranking on the index due to the large improvement in availability.”

The leap could be much bigger if the size of the home page was reduced, Filias adds. Keynote says retailers wanting fast-performing sites on smartphones should limit web pages to 50 elements weighing 500 kilobytes when on 4G LTE or Wi-Fi connections, 30 elements weighing 300 kilobytes when on 4G connections, and only 10 elements weighing 100 kilobytes when on 3G connections.

Keynote recommends a maximum page load time of 4.5 seconds on a blend of 3G and 4G networks, which is how the index measures mobile sites. The average mobile page load time for all 30 retailers on the index for the week ending Aug. 31 is 11.37 seconds. J.C. Penney had a success rate of 98.39%—an increase from 94.32% last week. The average success rate for all 30 retailers is 98.26%.

J.C. Penney declined to comment on its mobile site.

J.C. Penney was No. 14 on the Keynote index for the week ending Aug. 31—a jump of 11 spots from the previous week. Sears Holdings Corp. topped the index with a load time of 1.90 seconds, a success rate of 100%, and a score of 1,000 out of 1,000. (Keynote equally weights and combines load time and success rate to achieve a score). The Sears m-commerce site home page contains seven page elements that together weigh 49 kilobytes.

To see complete results (including response time, site availability, page weight in kilobytes, total page elements, and index score) for all 30 retailers on the Keynote Mobile Commerce Performance Index, click here.

Keynote measures, exclusively for Internet Retailer, 28 stand-alone m-commerce sites optimized for smartphones and two responsive design sites, which are single sites that render content in ways that fit the screen size of a device, including desktop PCs, tablets, smartphones and smart TVs. For the index, Keynote measures the smartphone versions of the responsive sites.

The 30 representative sites include merchants in multiple categories and channels, and of multiple sizes, ranging from such giants as Amazon.com Inc. to mid-sized retailers like Toolfetch.com LLC. Keynote tests the sites in the index every hour Monday through Sunday from 8:00 a.m. through midnight EDT, emulating the Apple iPhone 5 smartphone on two wireless networks: AT&T and Sprint, both using 3G, 4G and 4G LTE networks. Keynote runs the tests in Dallas, New York and San Francisco.

Keynote combines a site’s load time and success rate, equally weighted, into a single score. Given that both performance and availability are important, the score reflects the overall quality of the home page; a higher score indicates better performance. Scores also reflect how close sites are to each other in overall quality. The index average score is the midpoint among all the sites’ scores. To consistently rank high on the Keynote index, sites must hit availability targets of 99.5% or better and be faster than 10 seconds to load on average. Top-performing sites load in under five seconds.

Today, 20% of U.S. Internet-enabled mobile phone users have 4G or 4G LTE wireless data connections, 71% have 3G, and 9% have 2G, according to research firm Informa Telecoms & Media. And according to research and consulting firm Deloitte, 63% of U.S. smartphone users most often connect to the web on their devices on a Wi-Fi network.

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