Heidegger's Average Everydayness is neither a Statistical Measure nor a Theoretical Construct

Dasein’s average everydayness is not a statistical measure that may describe some Dasein more accurately than it describes another Dasein, i.e., Heidegger is not employing the term as if he were a social scientist. Instead, Dasein’s average everydayness is Dasein showing itself in itself and from itself. Dasein’s average everydayness shows Dasein as it is proximally and for the most part. Dasein’s average everydayness reveals certain structures essential to every kind of being that Dasein possesses and those structures are determinative for the character of each and every Dasein. Simply put, rather than being an average, the everydayness of Dasein describes the essential structure of each and every Dasein. See Being and Time (M&R transl.). at 37-38, in the German at 16-17.

Heidegger intends his phenomenology to be descriptive (not statistical or theoretical).