今天在 alexa 网站上发现，每个网站的评级详细页面，都加了一个按钮“Our Rangings have changed”。点击进去才知道，现在 alexa 升级了他们的评级系统，主要是采用了更广泛的数据来源。
原来的 alexa 数据主要是依靠安装了 alexa 的工具条的访问记录，这显然是非常不准确的，下面是官方的说明：
When Alexa began displaying rankings in 1998 it was with the goal of showing Alexa Toolbar users how popular any given site was within the Alexa community. We generated the rankings through an analysis of Internet usage by people who use the Alexa Toolbar. Since that time we’ve been delighted to see that the Alexa Rankings have become a yardstick by which website popularity is measured. We are grateful to the thousands of people who come to Alexa.com each day to check the Alexa Rankings.
Alexa 升级系统后， CodeBit.cn 的评级从60多万上升到40多万，看来数据来源是大了很多。