The reliability and validity of the Korean version of the Pittsburgh ...

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Sleep Breath (2012) 16:803–812 DOI 10.1007/s11325-011-0579-9

ORIGINAL ARTICLE

The reliability and validity of the Korean version of the Pittsburgh Sleep Quality Index Seung Il Sohn & Do Hyung Kim & Mi Young Lee & Yong Won Cho

Received: 13 May 2011 / Revised: 26 July 2011 / Accepted: 15 August 2011 / Published online: 8 September 2011 # Springer-Verlag 2011

Abstract Purpose 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. Methods 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. Results Cronbach's α 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 S. I. Sohn : D. H. Kim : Y. W. Cho (*) Department of Neurology, Dongsan Medical Center, Keimyung University School of Medicine, 194 Dongsan-dong, Jung-gu, Daegu 700-712, South Korea e-mail: [email protected] Y. W. Cho e-mail: [email protected] M. Y. Lee Preventive Medicine, Dongsan Medical Center, Keimyung University School of Medicine, Daegu, South Korea

PSQI-K for insomnia and narcolepsy were significantly higher than those for controls (p2, 2>1

1 1 1 1 1 1 1 1

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Fig. 1 The PSQI-K of each group

high degree of internal consistency between the total score of the PSQI-K and the seven component scores of the PSQI-K, which is comparable to the original PSQI [9]. The PSQI-K showed good internal consistency and test–retest reliability. Though the MAPI Korean version of the PSQI is very good and useful, our version was written more clearly for use by laymen and more closely matches the original. Post hoc analysis with the seven component scores of the PSQI-K in each sleep disorder group showed there were differences between subjects with primary insomnia, narcolepsy, and the healthy controls, which is comparable to previous studies [23, 24]. All the seven component scores of the PSQI-K gave significant differences between the subjects with primary insomnia and the

Fig. 2 Sensitivity and specificity of the PSQI-K in poor sleepers by the ROC. Sensitivity and specificity for correctly identifying poor sleepers were 0.943, and 0.844 on the basis of the cutoff point 8.5

healthy controls, while there was no significant difference in sleep onset latency and the sleep duration components between the patients with narcolepsy and the healthy controls. This most likely reflects the different clinical characteristics of the different groups. That is, the main complaint of the subjects with narcolepsy was excessive daytime sleepiness, rather than nocturnal sleep disturbances, so their sleep quality and sleep latency were not as poor as the subjects with primary insomnia. Although the component scores are helpful, the most important in discriminating between poor and good sleepers is the PSQI-K total score. The PSQI-K is useful in distinguishing different sleep disorders from good sleepers. The area under the receiver operating characteristic curve of the total score of the PSQI-K differentiated between “good” and “poor” sleepers. A cutoff score of 8.5 represents a sensitivity of 0.943 and specificity of 0.844, which is higher than the score of 5 in the original paper [9]. This may be due to the high severity of symptoms in the insomnia group. Carpenter's study in 1998 reported most subjects with sleep disturbances had scores greater than 8, which is similar to ours [1]. We also studied the overnight PSGs in all “poor” sleepers, which showed us their objective sleep characteristics. The sleep efficiency and sleep latency of the PSG had correlations with the PSQI-K score that were statistically significant but small in magnitude. The Buysse et al. study showed that the total score of the PSQI was weakly correlated only with sleep latency for all subjects. The Backhaus et al. study showed that the sleep efficiency, percentage of the sleep stage 2, and sleep latency had significant correlations with the total score of the PSQI [23]. However, the validation study of the Brazilian Portuguese version of the PSQI (PSQI-BR) by Bertolazi et al. showed no correlation between the PSQI-BR scores and PSG findings [14]. These findings may be related with the first night effect of the PSG and the subject's daily

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Table 5 Principal component analysis for PSQI-K components Components

Factors Factor 1

Sleep quality Sleep latency Sleep duration Habitual sleep efficiency Sleep disturbance Use of sleeping medication Daytime dysfunction

Factor 2

0.693 0.830 0.831 0.860 0.322

0.515 0.223 0.070 0.114 0.634

0.770 −0.029

0.139 0.880

fluctuation of sleep quality. Some poor sleepers, especially insomniacs, are often overly fault finding about sleep quality, compared to the overnight PSG findings. When we factor-analyzed the PSQI-K in our study, we divided the components into two factors, which is a little different from Cole et al. [17]. The PSQI-K components of sleep disturbance and daytime dysfunction were more closely associated, and the other components were more closely associated in our subjects. Our study has a few limitations. It was conducted locally within one sleep center in Korea, so this point could be considered a limitation on the validation study. The questions of the PSQI did not have local characteristics,

so there are no regional differences and therefore no need for any changes. Another country's study found there was no cultural adaptation process needed [14]. The second limitation was that the number of subjects with narcolepsy was relatively lower than those with insomnia. However, we had 394 subjects, and most subjects showed the objective sleep parameters through the PSG findings. And the third limitation was differences in age and sex between the groups. Narcolepsy is less frequent with increasing age. Therefore, it was actually difficult to adjust the other groups to the same age. We used the statistical technique, ANCOVA, to compensate for confounding factors such as age and sex. In addition, we analyzed the correlation coefficient to identify the effects of age on the PSQI-K score, which revealed that age did not have any effect. In summary, the PSQI-K is a valid and reliable screening tool to identify “good” and “poor” sleepers, which is comparable to the original version. It is used as a simple screening tool to identify “good” and “poor” sleepers and also useful to screen patients for the presence of significant sleep disturbances in Korea.

Acknowledgments Many thanks to Dr. Daniel J. Buysse, who granted us permission to use his questionnaire and who helped in our study. This work was supported by the brain research-promoting grant from Keimyung University Dongsan Medical Center.

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Appendix

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