Drinking Diary

Professor Bruce Lazarus of Purdue University's School of Hotel and Institutional Management has for the past seven years had his students in his hospitality class keep a "drinking diary" for a one week period. In the diary, students record their drinking behavior patterns, and any other observations they might have. Professor Lazarus is the only individual to read the diaries, and students can choose an alternate assignment if they do not want to keep the journal. Is the "drinking diary" an ethically acceptable assignment?