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.
Estimates are more reliable the closer a site is to being ranked #1. Global traffic ranks of 100,000+
are subject to large fluctuations and should be considered rough estimates.
If a site has Certified Metrics instead of estimated, that means its owner has installed code allowing us to directly measure their traffic.
These metrics have a greater level of accuracy, no matter what the ranking.