The possibility of grade retention has been shown to be a significant source of stress for students. In one study of childhood fears performed in the 1980s, the top three fears for US sixth graders were a parent's death, going blind, and being retained. After two decades of increasing retention practices, a repeat of the study in 2001 found that grade retention was the single greatest fear, higher than loss of a parent or going blind. This change likely reflects the students correct perception that they were statistically far more likely to repeat the sixth grade than to suffer the death of a parent or the loss of their vision.