I can't say I have even seen a consistent definition of binge drinking.
Normally, a binge is defined by the people taking a survey or writing a report. I have seen anywhere from 2 – 5 drinks defined as a binge. Such definitions are necessary for any statistical analysis, but then people take this definition, assume that it actually has some medical facts to back it up, apply it to their (or more often, other peoples) lifestyle and viola, a statistician has decided what a healthy level of drinking in a single sitting is, by choosing an arbitrary figure which seemed reasonable.
Has anyone seen any studies which define what a binge is from a medical standpoint?