The reliability and validity of the Korean version of the Pittsburgh Sleep Quality Index

The Pittsburgh Sleep Quality Index (PSQI) is a self-reported questionnaire that measures sleep quality during the previous month. The aims of this study were to analyze the reliability and validity of the Korean version of the PSQI (PSQI-K) and to evaluate its usefulness. We developed the PSQI-K, which involved translating the original PSQI into Korean and then translating back into English to check its accuracy. We tested the validity of the PSQI-K on a total of 394 individuals: 261 with poor sleep (primary insomnia, n = 211; narcolepsy, n = 50) and 133 with good sleep. All subjects completed the PSQI-K, 285 had overnight nocturnal polysomnography, and 53 were randomly selected for a retest with the questionnaire after 2-4 weeks without any intervening treatment. The mean PSQI-K global scores in each group were analyzed after adjusting for age and sex. Cronbach's alpha coefficient for internal consistency of the total score of the PSQI-K was 0.84 which shows high reliability. Sensitivity and specificity for distinguishing poor and good sleepers were 0.943 and 0.844 using the best cutoff point of 8.5. The total and component scores of the PSQI-K for insomnia and narcolepsy were significantly higher than those for controls (p < 0.05). The test-retest correlation coefficient was 0.65 for the total score (p < 0.001). There was no significant difference between the two values using the paired t tests. The PSQI-K is a reliable and valid questionnaire for evaluating sleep quality in patients with sleep disorders.