The effect of the emotion of guilt on how a student focuses on a problem was investigated in the Journal of Behavioral Decision Making (January 2007). 155 volunteer students as a sample participated in the experiment, where each was randomly assigned to one of three emotional states (guilt, anger, or neutral) through a reading/writing task. Immediately after the task, the students were presented with a decision problem (e. g., whether or not to spend money on repairing a very old car). The researchers found that a higher proportion of students in the guilty-state group chose not to repair the car than those in the neutral-state and anger state groups. Identify the population.