PR and Alexa both have something very important in common - they are both ridiculously unreliable and a bad gauge of your SEO. Let's begin with PR. Google's algorithm is based on an internal PR that they secretely assign to every webpage. However, this isn't the value that they display in the Google toolbar. In fact, the PR value they display is only updated every couple of months, and even then, isn't always reflective of their internal PR algorithm.
Now to consider Alexa: alexa gets its reporting from people who use the Alexa toolbar. But those people are just a small niche representation of the Internet population. For that reason, there is a huge bias for techies and people who frequent Alexa's network (Amazon.com). All in all, it's just pretty unreliable.
cscgal
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