Shows the amount of different visitors per year.
It is often used in analyses, that don't show a development over time (e.g. campaigns).
Example:
A visitor accesses the website in October, November and December. He is counted only once (e.g. in the campaign analysis).
In case a visitor accesses the website in 2 years (e.g. December 2016 and January 2017), he is counted twice (once per year).
Visitors are identified either based on the cookie and/or a submitted customer ID.
Don't use this metric in time analyses, that show a smaller time interval than "Years" (e.g. "Days", "Hours"...). In this case the calculation is done automatically per used time interval.
If you use the metric in a year analysis (dimension "Years") double countings can occur. All users, whose visit lasted from December 31 to January 1 are counted again, when another visit is made in the year. In this case, use the metric "Visitors".