The insomnia severity index consists of seven questions evaluating nighttime sleep difficulties, sleep dissatisfaction, and impact of insomnia on the quality of life. Time-frame of such evaluation is in the two weeks before the test. Each question is rated on a five-point Likert scale ranging from 0 (not at all) to 4 (extremely) with a maximum total score of 28. Scores from 0 to 7 mean no clinically significant insomnia, 8 to 14 mean subthreshold insomnia, 15 to 21 mean moderate clinical insomnia, and 22 to 28 mean severe clinical insomnia.