The website owner has installed an Alexa Certify Code on the pages of their site and chosen to show the metrics publicly.
Not all websites implement our on-site analytics and publish the results.
For these sites, we show estimated metrics based on traffic patterns across the web as a whole.
We identify these patterns by looking at the activity of millions of web users throughout the world, and using data normalization to correct for any biases.
The more traffic a site gets, the more data we have to calculate estimated metrics.