This tests how popular this website is compared to other websites, and whether popularity is rising or falling.
This is a simple at-a-glance performance measurement of how popular a website is versus others. It is particularly useful where more detailed information is not available (e.g. most organizations don't have access to their competitors analytics).
The Alexa ranking is used. This is based on a very large sample (several million) of web users, all of whom share many browser toolbars which record their viewing history. Generally Alexa can give rankings for websites in the top 5 million – results are much more accurate the higher the ranking. There are some biases in the data, but generally it is still very useful as long as it is used appropriately in context (e.g. more as a relative measure, not an absolute – "website A is more popular than website B").
The only way to improve this score is to be gradually improving the popularity of your website. Don't assume that websites must always score a perfect 10 for this test.