I’ve already written several blog posts about Alexa and how notoriously bad its statistics are. Not really surprising that they are bad if you know how the data for those statistics is gathered. For the bulk of their data Alexa relies on people installing the Alexa Toolbar (or a toolbar that passes information to Alexa). It’s this toolbar that monitors to which websites you go and how you end up on them.
This has as a result that demographic, used browsers, and even the country visitors are from influence the data that Alexa gathers about a website. This can introduce serious artefacts and biases into the collected data and basically makes the statistics generated from it worthless. At best it can give you an idea about how well a website is doing, but that doesn’t mean that what you’re seeing matches reality. I’ve already written a far more detailed blog post about how Alexa works and why you never should rely on the data it provides; it’s just too unreliable.