The Cheesecake Factory’s mobile site home page didn’t lose any weight, but it sliced off more than half the time it took for the home page to finish loading, or the visually complete time, for the week ending Jan. 17. And the results were pretty sweet.

TheCheesecakeFactory.com surged 12 spots on the AppDynamics/Mobile Strategies 360 Performance Index on 3G to No. 9 from No. 21 the previous week. The index monitors the site speed and general performance of 30 mobile sites on both 3G and 4G mobile networks.

The Cheesecake Factory’s visually complete time improved to 6.8 seconds from 14.2 seconds the previous week. However the weight of its home page remained similar week to week, at 1.62 megabytes this week compared to 1.52 megabytes last week, as did the number of resources loaded, at 39 this week compared to 40 last week.

On the 4G index, TheCheesecakeFactory.com also rose 13 spots to No. 3 from No. 16 the previous week.

The only thing that appeared to have changed from week to week on The Cheesecake Factory’s mobile site is an interstitial banner that overlays the whole screen before the site appears, says Peter Kacandes, senior product marketing manager, mobile, web and synthetics, for AppDynamics.

“The site now puts up a simple dialog pop-up window to sign up for an email distribution list with a transparent overlay and a single large background image that changes in carousel once the user has clicked out of dialog box,” Kacandes says. Cheesecake Factory did not respond to a request for comment.

Amazon.com Inc. fell on the 3G index this week to No. 15 from No. 11.

“They added a little over 100 kilobytes to their page weight, but that was enough to increase their visually complete time by a little over a second,” Kacandes says. Amazon did not respond to a request for comment.

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.

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.

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 Jan. 17, the average Speed Score for 3G was 9.4 seconds compared to 9.6 seconds a week earlier. The average first render was 6.9 seconds compared to 6.7 seconds a week earlier.

Visually complete average was 15.6 seconds compared to 15.9 seconds the previous week. Average number of elements loaded was 97.3 compared to 97.0 the previous week. Average home page weight was 1.8 megabytes, the same as the previous week.

On 4G, the average Speed Score was 5.7 seconds, the same as the previous week. The average first render was 4.0 seconds compared with 3.9 seconds the previous week.

Visually complete average time was 9.2 seconds compared to 9.3 seconds the previous week. Average number of elements loaded was 97.6 versus 96.8 versus a week earlier. And average home page weight was 1.8 megabytes compared to 1.9 megabytes the previous week.

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 Jan. 17.