Having a fast start doesn’t guarantee first place.

A mobile site loading on 3G, for example, that quickly loads the first elements on the page, but takes a long time to finish drawing everything, is not going to be No. 1 in the AppDynamics/Mobile Strategies 360 Index. The index ranks 30 mobile sites based on their performance on both 3G and 4G.

JCrew.com, of J. Crew Group Inc. is feeling that pain this week on the 3G index. Last week J. Crew had the No. 4 spot on the index, and fell to No. 8 this week almost entirely because of an increase in the visually complete time, says Peter Kacandes, senior product marketing manager, mobile, web and synthetics, at AppDynamics. JCrew’s visually complete time, or the time it took for the web browser to complete drawing the visual elements of a page, increased to 9.7 seconds from 8.1 seconds the previous week.

This 1.6-second increase is the reason for the apparel retailer’s fall in the index, Kacandes say. J. Crew’s page load decreased to .89 megabytes from 1.5 megabytes, and the number of resources loaded by a page stayed the same at 57. First render time, or the time it took for the web browser starts drawing the visual elements of a page, also stayed the same for last week to this week at 5.1 seconds

“One of the causes could be an increase in the response available time of the server, which includes the server connection time and the time it takes the server to respond with the first byte of data,” Kacandes says.

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A J. Crew spokeswoman says the retailer did not see any performance issues during this time.

AppDynamics also discovered a large increase in the time it takes to create the JCrew index.jsp page, which is a Java Server page that is the main container page for the home page content. Without access to the back end of the site, Kacandes can only guess what caused the increased time to create the index.jsp page.

“It is critical for companies to understand how changes in web site design, architecture, or infrastructure changes can affect the performance of their web sites, especially as they are perceived by the end user,” Kacandes says.

Also of note this week, HealthCare.gov moved up eight spots to No. 10 from No. 18 in the 3G index because of a change in site content, Kacandes says. HealthCare.gov’s page weight decreased to 1.41 megabytes from 2.09 megabytes a week earlier.

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.

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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 page.

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

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

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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 earlier rather than later. The earlier a mobile site 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 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.

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 the week ending Sept. 6, the average Speed Score for 3G was 8.7 seconds compared with 9.2 seconds a week earlier. The average first render was 6.1 seconds compared with 6.2 a week earlier.

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Visually complete average was 14.2 seconds compared with 15.3 seconds the previous week. Average number of elements loaded was 85.3 compared to 86.3 a week earlier. Average home page weight was 2.0 megabytes compared with 2.5 megabytes, a week earlier.

On 4G, the average Speed Score was 5.2 seconds compared with 5.3 seconds last week. The average first render was 3.6 seconds, the same as a week earlier.

Visually complete average time was 8.3 seconds compared with 8.7 seconds the previous week. Average number of elements loaded was 83.8 versus 84.5 a week earlier. And average weight was 1.9 megabytes compared with 1.7 megabytes a week earlier.

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 Sept. 6, 2015.

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