Issue link: https://read.uberflip.com/i/1146286
104 | Chapter 15: Deconstructing 10 Top Sites Not surprisingly, page weight and response time are strongly correlated, with a cor- relation coefficient of 0.94, as shown in Figure 15-1. This makes sense—adding more components or larger components to the page makes it slower. Plotting page weight and response time throughout the development process is a worthwhile analysis for any web page undergoing performance improvements. YSlow grades are a strong indicator of the response time of a page, as shown in Figure 15-2. A high (good) YSlow grade indicates a well-built page that is fast and lean. A page with a low (bad) YSlow grade is probably going to be slow and heavier. Since the YSlow grade is inversely related to response time and page weight, the inverse YSlow grade is plotted in Figure 15-2. YSlow grades are typically indicated as A, B, C, D, or F, but behind the letter grade is a numeric score on the scale 0–100. Yahoo! doesn't quite follow the curve. It has the second-best YSlow grade (its score is A, at 95, which is slightly lower than Google's A, a perfect 100) and response time, even though it's the fourth-heaviest page. The Yahoo! home page team is a long-time consumer of these performance best practices, and therefore scores well in YSlow and is able to squeeze more speed out of their page. Amazon's YSlow grade also doesn't reflect the page weight and response time. The main reason for this is the large number of images in their page (approximately 74 images). YSlow doesn't subtract points for images, so the Amazon page scores well, but performs slowly. In general, we see that following these best practices results in a faster page. The cor- relation coefficient for inverse YSlow grade and response time is 0.76, indicating a strong correlation. This has been my experience in working with product teams at Yahoo!. As pages are changed to adopt one rule after another, their response times Figure 15-1. Page weight and response time are correlated Amazon AOL CNN eBay Google MSN MySpace Wikipedia Yahoo! YouTube Response time Page weight