Stat question

QUESTION 12 A researcher from this same study presents the results of their estimation analysis on the number of times a person drank alcohol in the past 30 days. They state the following conlusion: \"Based on our sample of 400 people we found that the mean number of times a respondent drank alcohol was 15 times in the past 30 days, with a margin for error of +l- 2 times." A grumpy guy in the back (ok, it's me), says the researchers are missing something. What crucial piece of information would a very particular statistician want to see in this interpretation? Why is it important for this piece of information to be reported