Relationships between the Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and clinical/polysomnographic measures in a community sample

Abstract

Study objectives: 1) To characterize PSQI and ESS scores, and their relationship to each other, in an adult community sample; 2) To determine whether PSQI and ESS scores, in combination with each other, were associated with distinct demographic, clinical, and sleep characteristics.

Methods: The PSQI, ESS, clinical rating scales, sleep diaries, actigraphy, and home polysomnography were collected from 187 community-dwelling adults (mean age 59.5 years, 47.1% women, 41.2% African Americans) as part of a study investigating novel cardiovascular risk factors. Correlations, cluster analysis, principal components analysis, MANOVA, ANOVA, and regressions were used to characterize the relationships between the PSQI, ESS, and other study variables

Results: Mean PSQI score was 6.3 (3.4), and mean ESS score was 8.2 (3.9). PSQI and ESS correlated weakly with each other (r = 0.16, p = 0.03), but segregated from each other on principal components analysis. Groups of participants categorized by either cluster analysis of PSQI and ESS scores, or by scores above or below traditional cut-off values, differed from each other on psychological/stress symptoms and quantitative and qualitative sleep diary measures, but not on actigraphic or polysomnographic measures. Specifically, higher PSQI scores were associated with female sex, greater psychological distress, and greater sleep disturbance on sleep diaries.

Conclusions: The PSQI and ESS measure orthogonal dimensions of sleep-wake symptoms, but neither is related to objective sleep measures. The PSQI is more closely related to psychological symptom ratings and sleep diary measures than the ESS. These instruments are not likely to be useful as screening measures for polysomnographic sleep abnormalities.

Figure 1

Frequency distributions of the PSQI (A) and ESS (B).

Figure 2

Scatterplot of PSQI and ESS scores. Different symbol shading and sizes correspond to the number of subjects at a particular PSQIESS score.

Figure 3

Historgram of PSQI-ESS Scores by Empirically Defined Clusters. Scatterplot of PSQI and ESS scores showing the distribution of subjects identified with K-means cluster analysis. Different symbols correspond to the four clusters.