“When you used alcohol during the last year, how often did you use it in each of the following situations?…When you were alone.” Response options were 1 = “Not at all” 2 = “A few of the times” 3 = “Some of the times” 4 = “Most of the times” 5 = “Every time.”

And they're comparing the "not at all" responses against all of the other ones. I understand they're analyzing data that already exists, so they don't get to go back in time and start asking a different question in 1977 when the survey begins, but I'm not sure how useful this is to the current analysis without some qualifier like "When you had three or more drinks in one day."