If you were to read the results of a study showing that daily use of a certain exercise machine resulted in an average 10-pound weight loss, what

If you were to read the results of a study showing that daily use of a certain exercise machine resulted in an average 10-pound weight loss, what more would you want to know about the numbers in addition to the average, before trusting the results? (Hint: Do you think everyone who used the machine lost 10 pounds?)