We are continually assessing and updating our direct measurement tracking to ensure that you get the most accurate metrics possible. On September 21, 2017, we made an update to how the certified visits metric is calculated in order to improve its accuracy.
Although most sites are not affected by this update, some Alexa Pro subscribers who have certified their site will notice a change in the number of Visits, Visit Breakdowns, or Minutes/Visit reported in the private Certified Site Metrics section of their account starting on September 21, 2017.
This update does not affect the Alexa rank, Monthly Unique Visitor estimates, Reach or any of a site’s public metrics. Any sites that are not currently certified have not been affected.
Alexa strives to calculate unbiased measurements of actual traffic on your site as part of our Certified Metrics service. However, we do understand that the way that people access and interact with sites changes over time and we frequently assess our data to make sure it is still relevant and accurate.
If you are seeing a discrepancy or change in your Certified metrics that is unrelated to Visits or Minutes/Visit, please check out this article: Why does the directly-measured data differ from my other analytics package?