More Evidence That Compete, Alexa and Quantcast are Largely Bollocks
Whenever I get a chance, I discourage marketers (or anybody else) from trusting web metrics companies like Quantcast, Alexa or Compete. In my experience, the numbers they report are consistently unreliable. I did a little ad hoc analysis to illustrate this point.
The publishers of the social news site Reddit provide further evidence of this phenomenon. They posted a screenshot from their Google Analytics account, indicating that their site typically receives about 8 million unique visitors a month.
They then compare these results with Compete (927,000 visitors), QuantCast (about 5 million) and Neilsen (625,000). Clearly none of these numbers are particularly useful to somebody trying to gauge the popularity or influence of a particular site.
It’s shameful how frequently the tech and marketing industries trust these sites. It’s a classic illustration of how people prefer highly dubious or inaccurate statistics over none at all.
In our book, we quote SEO guru Vanessa Fox on this topic:
All of the services are fairly notoriously unreliable. They all use different methods for gathering data that make them inaccurate by nature. Alexa, for instance, uses the Alexa Toolbar, which is skewed toward a certain user demographic. These tools are useful in a couple of ways, however: for trending over time and for comparisons. If you use one tool to gather data on these two things, then although the data will be unreliable, it should be equally unreliable over time or among sites, so the trending should be fairly accurate.
What’s the best way to determine a site’s popularity? Ask the site’s owner.
ThompsonPaul 
Ibid