Introduction
Emotional intelligence is the ability to understand emotions in self and others. Evidence suggests that emotional intelligence capabilities, including self-awareness, interpersonal communication, acceptance skills, and interpersonal adaptability, are associated with better adjustment. Although these traits are not as important as intelligence quotient (IQ), they are equally important in achieving a successful life [2]. Also, good sleep quality is a predictor of having a positive mood and feeling of energy and is related to physical and mental health [4]. Various studies have shown that emotional intelligence can have a great impact on sleep and its components, and people with higher emotional intelligence can experience optimal sleep quality [6, 7].
Adolescence is a period when a person has the ability to think more about the present and dream about the future, and experience more complex relationships. As a person encounters new experiences, these unfamiliar situations bring new and possibly intense positive and negative emotions. Therefore, a person needs emotional intelligence skills to regulate emotions and behavior [16]. Not much research has been conducted on the relationship between sleep quality and emotional intelligence, especially in children and adolescents. Also, these factors are important as a basis for success in various aspects of life (family, education, and career), especially in teenagers as a dynamic population of the country. This study aimed to investigate the relationship between emotional intelligence and sleep quality in female high school students.

Methods
This cross-sectional study was conducted on 284 female high school students in Rasht in 2019-2020, selected by cluster sampling. The education districts of Rasht were considered clusters, and one school from each district was randomly selected from the list of schools. Online questionnaires and consent forms were made available to students at www.porsline.ir. To collect the data, the demographic, the Bar-On emotional intelligence, and the Pittsburgh sleep quality index (PSQI) questionnaires were used. Data were analyzed by IBM SPSS statistics software, version 22. Quantitative data were reported as Mean±SD, and qualitative data as numbers and percentages. Considering the non-normality of the data distribution, the relationship between sleep quality and emotional intelligence was assessed using Spearman’s correlation coefficient. The relationship between the evaluated variables and the two-mode variable of sleep quality (score more than five) was assessed by multiple logistic regression analysis. P<0.05 was considered statistically significant.

Results
Out of 285 students who were given the link to the questionnaires, one person was excluded from the study due to incomplete questionnaires. Therefore, 284 students were included in the study. The mean age of participants was 13.94±0.95 years, and the mean previous grade point average (GPA) of participants was 19.61±0.89. The mean total score for emotional intelligence and sleep quality were 334.95±42.82 and 4.71±3.20, respectively. Most participants (69%, 95% CI, 63.4%-74.3%) had good sleep quality (the sleep quality questionnaire score was equal to or less than five). Among the subscales of sleep quality, the subscales of sleep latency with a mean of 1.19±0.92 and the use of sleep medication with a mean of 0.09±0.39 had the highest and the lowest mean scores, respectively.
A negative correlation between the total scores of emotional intelligence and sleep quality was found by Spearman’s correlation coefficient (r=-0.427, P<0.001) (Figure 1). The multiple logistic regression showed an inverse relationship between poor sleep quality and emotional intelligence score (OR=0.98, P<0.001). There was no association between demographic variables and sleep quality (P>0.05).


 
Discussion
In this study, a significant relationship was found between sleep quality and emotional intelligence. With the increase in emotional intelligence, the chance of poor sleep decreased. Consistent with our study, in Brand et al.’s study, about 49% of adolescents had moderate to severe sleep problems. These people were more sleepy during the day and had weaker emotional skills [17]. However, in the study by Heidari et al. on female high school students, the results were contradictory, and there was no significant relationship between emotional intelligence and sleep quality [14]. 
According to the results, about one-third of the participants had poor sleep quality. In the study by Fazlali et al., the rate of poor sleep quality in female students was reported as 41.42% [33]. In recent years, factors, such as using smartphones while sleeping [34], reducing physical activities [36], consuming addictive substances, and worrying about academic performance [37] were related to the higher probability of poor sleep quality in adolescents.
In the present study, sleep quality had no significant relationship with students’ demographic characteristics, including age, GPA of the previous year, and physical illness. Some other studies showed that sleep quality has a significant relationship with age, and adolescents with older age had lower sleep quality [30, 31]. However, in line with our study, in the survey conducted in Brazil, no relationship was observed between the age and sleep quality of adolescents [32].
Considering the relationship between higher emotional intelligence and optimal sleep quality, it seems that with proper planning and training for teenagers, it is possible to increase the level of emotional intelligence and improve the quality of students’ sleep, and as a result, improve the learning process, interpersonal relationships and their self-esteem.
In order to further generalize the findings and reduce the limitations, it is suggested to conduct a larger and multicenter study with a higher sample size in different age and gender groups.

Ethical Considerations

Compliance with ethical guidelines
This study was approved by the Ethics Committee of Guilan University of Medical Sciences (Code: IR.GUMS.REC.1399.044).

Funding
There was no funding from any governmental, private, or non-profit organizations.

Authors' contributions
Conceptualization, study design and critical revision of the manuscript for important intellectual content: All authors; Analysis: Robabeh Soleimani and Fatemeh Eslamdoust-Siahestalkhi; Drafting of the manuscript: Robabeh Soleimani and Fatemeh Eslamdoust-Siahestalkhi; Data gathering: Mohadese Najafi Chakusari and Shima Payandeh; Supervision: Robabeh Soleimani.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the Department of Education, school management, and the students who accompanied us in this research.

 

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