With increased focus on privacy, many internet users block use of cookies or other forms of tracking identity. This means that the platforms that monitor user traits (age, gender, buying habits, and preferences) aren’t able to collect that data. When reported back to us, those users just get marked as “unknown.” Some DSPs are better able to track user traits than others, but all are limited by user preferences.

You may not always find unknown values in your campaign's analytics and instead you'll see the total number of known values in an effort to make the data more understandable.