A big part of speed is perception.

If two sites take the same number of seconds for the web browser to finish drawing the home page (also known as visually complete time), but one site shows more content sooner, a consumer will perceive that site to be faster, says Peter Kacandes, senior product marketing manager, mobile, web and synthetics, for AppDynamics.

This perception matters in the AppDynamics/Mobile Strategies 360 Performance Index and factors into a mobile site’s Speed Score, Kacandes says. The index ranks the site speed and general performance of 30 mobile sites by their Speed Scores. To come up with a Speed Score, the index looks at each mobile home page’s visually complete time, start render (the amount of time it takes for the browser to start loading the page), page weight (how heavy a page is in megabytes), and resources loaded (the number of elements on a mobile home page).

“That is what the speed index essentially captures,” Kacandes says. “If all of the metrics stay the same, yet the speed index (ranking) changes, that is an indicator that the site made a change that affected how content is rendered over time, whether intentional or not. A better speed index (ranking) will result in an overall perception of better performance by the end user, all else being equal.”

This is the reason that J. Crew Group Inc.’s mobile site dropped five spots on the 3G index for the week ending March 13, Kacandes says. In fact, J. Crew reduced the number of elements on its home page by 100 kilobytes compared to a week earlier, the time it took for the web browser to start drawing the mobile home page stayed the same week to week and the visually complete time was actually faster by 0.6 seconds. However, J. Crew dropped to No. 13 from No. 7 on the 3G index.

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“Sometimes you have to look beyond just the metrics and investigate further to understand how content is rendered and how that affects performance,” Kacandes says. “J. Crew’s speed score was slower by 1.3, indicating that more of the content is being rendered later in the cycle, reducing the overall perception of speed by the user.”

J. Crew is in the process of rolling out a new mobile site, and comparison metrics could be off, a J. Crew spokeswoman says.

Also on the index, American Airlines Inc., for the second week in a row, dropped on the 3G index. America Airlines slipped five spots to No. 19 from No. 15 the previous week. The mobile site’s page weight increased by 100 kilobytes, the visually complete time increased by more than two seconds and the time it took for the browser to start loading the home page increased 1.2 seconds.

The increase in the mobile site load time is because of enhanced security measures, an American Airlines spokeswoman says.

“We’ve enhanced security on our mobile site and, for some mobile users, it’s impacting performance,” she says. “We are hard at work to optimize our site to these new measures, but safety and security are the top priorities for our airline.”

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The exclusive AppDynamics/Mobile Strategies 360 Index tracks key mobile site metrics across a range of sites to calculate a weekly average Speed Score on both 3G and 4G mobile carrier networks. The index represents a snapshot of mobile site performance across industries, including retailers such as HSN.com, insurance companies such as NorthwesternMutual.com and restaurants such as McDonalds.com.

AppDynamics each week measures performance metrics of both 3G and 4G networks for each of the 30 sites in the index to determine each site’s Speed Score.

They include:

First render: The time, (in seconds) it takes until the web browser starts drawing the visual elements of a home page.

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Visually complete: The time (in seconds) it takes until the web browser has completed drawing the visual elements of a home page.

Number of elements loaded: The number of resources loaded by a home page.

Complete load: The size of the home page when all data is loaded (in megabytes).

Using these metrics, the index calculates the Speed Score. The Speed Score is a ratio that rewards businesses for displaying more visual content on the mobile home page earlier rather than later. The earlier a mobile site home page looks complete to a consumer, the better the mobile experience for the visitor, even if a few remaining elements are displayed later. A site with a higher ratio of content displayed earlier will have a better Speed Score than a site with the same visually complete time but a longer first render time.

For example, site A may have a visually complete home page load time of three seconds, loading 90% of its content in the first second and the remaining 10% in seconds two and three. Site B may have the same three-second visually complete time, but present zero content in the first two seconds and 100% in the third second. The sites have identical visually complete times, but Site A will be perceived as much faster, and will earn a better Speed Score as a result.

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The index displays the average across the 30 mobile sites for each metric as well as the average Speed Score on both 3G and 4G networks for each mobile site.

For the week ended March 13, the average Speed Score for 3G was 10.0 seconds compared to 9.8 seconds the previous week. The average first render was 6.9 seconds compared to 6.8 seconds the previous week.

Visually complete average was 16.0 seconds compared to15.4 seconds the previous week. Average number of elements loaded was 98.9 compared to 100.2 the previous week. Average home page weight was 1.7 megabytes compared with 1.6 megabytes compared the previous week.

On 4G, the average Speed Score was 5.8 seconds compared with 5.7 seconds the previous week. The average first render was 4.1 seconds compared with 4.0 seconds the previous week.

Visually complete average time was 8.8 seconds compared with 8.7 seconds the previous week. Average number of elements loaded was 99.1 versus 100.2 a week earlier. And average home page weight was 1.7 megabytes, the same as the previous week.

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The index is accompanied by a chart on MobileStrategies360.com that is refreshed weekly to illustrate how each mobile site performs as well as index averages. Click here to access the performance chart for the week ending March 13.

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