In a Study Reported in the July 6, 2007, Issue

Short Answer

In a study reported in the July 6, 2007, issue of the journal Science, researchers studied 396 American college students and kept track of each student's gender and also how many words they spoke in a day. They found that women spoke an average of 16,215 words per day and men an average of 15,669 words per day.
-Specify another variable that could have been recorded about the observational units in this study.