LaFrance and Hecht(1995) studied the social significance of human smiles. The experimenters asked the subjects(136 students) to rate the likelihood that the person in the picture is guilty. The higher the score the more lenient the subjects were. In the spreadsheet for In-Class Lecture 3 exercise, you will find the types of facial expression and the leniency score. Can you conclude at 95% confidence that smiles increase leniency (i.e. Is the difference between the population mean of leniency scores of smile and neutral expression greater than 0)?
LaFrance, Marianne, and Marvin Hecht. “Why Smiles Generate Leniency.” Personality and social psychology bulletin 21.3 (1995): 207–214. Web.