Correlation Study among the Bedtime Procrastination and Sleep Disorder, and Depression of University Students during COVID-19 Pandemic in Korea
Sung-Min Son1,A-Reum, Park1*
1,2Professor, Department of Occupational Therapy, JeonjuKijeon College 267 Jeonjucheonseo-ro, Wansan-gu, Jeonju-si, Jeollabuk-do, 54989, Republic of Korea
Corresponding author*: A-Reum, Park, E-mail: [email protected]
ABSTRACT
The purpose of this study is to analyze the correlation among the bedtime procrastination and sleep disorder, and depression of university students during the COVID-19 Pandemic in Korea. The subjects were 120 university students in Korea. The assessment of bedtime procrastination was used by the bedtime procrastination scale and the assessment of sleep disorder was used by the sleep disorder questionnaire. The assessment of depression was used by the self-rating depression scale. All the assessment was performed by the Google online survey in consideration of COVID-19 Pandemic in Korea. To verify the relationship between variables, the Correlation Analysis was performed. As the results of the correlation among variables, all the results among the variables showed the positive correlation and these showed statistically significant difference.
COVID-19 pandemic acts as a factor to effect on the increase of bedtime procrastination, sleep disorders and depression level. Thus, the multi-faced and detailed analysis of these should be performed.
Keywords
Bedtime procrastination, COVID-19 pandemic,Depression, Sleep disorder, University student
1. Introduction
To date, the new virus Coronavirus disease-19 (COVID-19), which is scattered around us and is continuously infected, has microbiological characteristics that are transmitted into the air ad resembles past infectious disease. However, even stronger transmission power causes the major changes and problems in daily life[1]. In order to prevent infection and direct transmission, it is most important to observe precautions such as washing hands, wearing a mask, and practicing social distancing [2]. Among various preventive measures during COVID-19 pandemic, social distancing indicates the active behavioral measures to maintain social distance from others in order to prevent COVID-19 infection. These social distancing involves avoiding crowded areas and refraining from physical contact with others when possible [1].
In Korea, through the application of social distancing by the COVID-19 pandemic, the educational process is changed into un-contact lectures in all of the educational institutions [3]. In the process of job performance, workplaces are operated in the form of working at home and the operational restrictions are applied to religious facilities and hospital [4]. As a results, daily activities were restricted, and as the period of separation of each individual became longer, various psychological problems began to be caused, such as anxiety, depression, and stress [5].
Generally, these negative psychological states increase the occurrence of various problems, such as inducing negative physiological changes in the body and disproportionately changing the physical rhythm [6-7]. Accordingly, these problems causing in daily life decrease the performance level of various activities of daily living and effect negatively on the various activities such as sleep [8].
Sleep is vital for recovery and maintenance of health and improve the performance level of activities of daily living and quality of life. Sleep includes quantitative elements, such as time to fall asleep, actual sleep time, wake-up frequency during sleep, etc, and qualitative elements, sleep depth, satisfaction about sleep, quality of sleep, etc[9]. These sleep is closely related in the health and proper sleep help the body to form optimal health condition by recovery and recharge the energy. However, inappropriate sleep does not restore the body condition, and induces the sleep disorders that affect normal life rhythms[10].
Bedtime procrastination is one of the importantfactorsto interfere with sleep and is defined as a behavior that delays sleep through various activities such as watching TV and using smartphone before sleep in daily life [11]. Recently, with the increase of spread and use of a smartphone rapidly, the frequency and time to use a smartphone before sleep is continuously increasing, which disturbs the sleep and delays the time to sleep significantly[12]. The previous studies reported by the Lee [13] and Zou et al.[14] determined that these bedtime procrastination is closely related to psychological depression, and are significant associated with decreased concentration, anxiety, and depression. Additionally, the studies suggested that the increase of bedtime procrastination including the use of the smartphone before sleep contribute to delay sleep time, interfere with the sleep, and reduce the quality of sleep [15].
University students begin to form the healthy lifestyles, and establish appropriate physical and emotional changes as adults in their twenties[16]. Throughout university life, they grow as members of society by deciding their own career paths, preparing for employment, and gaining competence as preliminary specialists for each major [17]. However, they are facing the effects of COVID-19 pandemic, limiting the opportunities to enjoy university life with the application of un-contact lecture, and causing considerable problems in adapting to university life. Especially, through the participation in un-contact lecture from the COVID-19 pandemic, these interferes with the major satisfaction and commitment level, and contributes to significantly decrease university students’ academic achievement levels. Additionally, these problems affects directly to the employment process among university students, such as the delay of employment and certification examinations.
Accordingly, COVID-19 induces significant changes related in the university life and activities of daily living the among university students and also contributed to increase the significant pain in psychological factors such as increasing the depression level[16]. These physical and psychological problems acts directly to reduce sleep quality and sleep time during sleep, and create sleep patterns irregularly, inducing sleep disorders such as insomnia [18-20]. The studies related in the sleep and depression among university students were reported continuously [18][21]. However, there was no study for analyzing the relationship between sleep problems and depression among university students during COVID-19 pandemic.
Thus, the purpose of this study is to provide the basic information about the correlation results among bedtime procrastination, sleep disorder, and depression of university students
2. Methods 2.1 Study subjects and period
Study subjects were 120 university students at the J collage in J city. In the selection of study subjects based on Faul et al. [22] and this study’s purpose and the statistical analysis, the G*Power 3.1 software was used to generate the study subjects’ sample size (a= .05, effect size=
.03, power= .90, two-tailed test). As the results of the sample size generation, this size was determined to be suitable for more than 114 people. Accordingly, 125 university students were recruited and then among them, 5 students who disagreed to participate in this study (n=2) and responded inappropriately to this study’s survey (n=3) were excluded. Finally, a total of 120 study subjects participated.
Before the participation in this study, the enough introduction about the purpose and method of this study was provided. For these, the purpose and method of this study was understood enough.
After enough understanding this, they agreed to voluntary consent. The voluntarily consents of the participation in this study was provided as the paper. The study was performed 1 months from October 1 to 30 in 2020.
2.2 Study procedures
To analyze the correlation between bedtime procrastination and sleep disorders, and depression among the university students during COVID-19 Pandemic in Korea, correlation Analysis were performed. Before the study, to verify the validity of this study’s process and methods, the contents validity index (CVI) was performed as the preliminary feasibility test. As the results of the CVI, the validity of the process was 0.90 points and the methods was 0.90. As the obtaining the points over the 0.59 points by the 11 professionals, the results could be considered to be of greater validity [23]. Based on these, this process and methods applied to the subjects.
The assessments of bedtime procrastination and sleep disorder, and depression were performed to the type of online survey using the Google online survey in the consideration of the COVID-19 Pandemic in Korea. Before the assessment, the enough instruction about the purpose and methods of the assessment was provided to them. The assessment was performed by the both researchers who are occupational therapist.
2.3 Bedtime procrastination assessment
To analyze the bedtime procrastination, the Bedtime Procrastination Scale (BPS) developed by Kroese et al. [24] was used. The BPS is a useful assessment to measure the activity level to delay the bedtime. The bedtime procrastination is an activity by lacking the self-modulation ability, and this means as an activity of the watching TV and wandering around to delay the sleep despite no external event beyond control and expected negative results. The items of the BPS are consisted of the 9 items and each item is measured by the 5 points Likert scale from 1 to 5 points. The scoring of 2, 3, 7 and 9 items are reversed. The total score of BPS is from 9 to 45 points and the higher total score indicate a higher level of bedtime procrastination. Cronbach’s a of BPS is .92 [24].
2.4 Sleep disorder assessment
To analyze the sleep disorder, the Sleep Disorder Questionnaire (SDQ) developed by Oh et al.
[25] was used. This is a useful assessment to measure the level of sleep disorder by the items about the sleep pattern, self-sleep evaluation, results in sleep, and the factors influencing the sleep disturbance nowadays. The items of the SDQ are consisted of 15 items and each item is measured by the 4 points Likert scale from 1 to 4. The scoring of 11 and 13 items are reversed. The total score of KSS is from 16 to 60 points and the higher total score indicates a higher level of sleep disorder. The Cronbach’s a of KSS is .92 [25].
2.5 Depression assessment
To analyze the depression, the Zung’s Self-Rating Depression Scale (SRD) developed by Zung[26] was used. This is a useful assessment to measure the level of general depression by the self-report evaluation. The items of SRD are consisted of 20 items. Specifically, 2 items measure the level of general depression, 10 items measure the level of psychological depression symptom, and 8 items measure the level of physiological depression symptom and each item is measured by the 4 points Likert scale from 1 to 4 points. The scoring of 2, 5, 6, 11, 12, 14, 16, 17, 18 and 20 items are reversed. The total score of SRD is from 20 to 80 points and the higher total score indicates a higher level of depression. The interpretation of the results of total score was as follows: 1) 20-49 indicating a normal range, 2) 50-59 indicating mild depression, 3) 60-69 indicating moderate depression, and 4) 70 and above indicating severe depression that requires immediate treatment, including drug. The Cronbach’s a of SRD is .82 [27].
2.6 Statistical analysis
The collected data was encoded and analyzed using SPSS 23.0 ver. Descriptive statistics was used to analyze the general characteristics of study subjects and the results of bedtime procrastination, sleep disorder, and depression. The Correlation Analysis was used to analyze the relationship between the bedtime procrastination and sleep disorder, and depression. The significant level was set at the 95%.
3. Results 3.1 General characteristics of study subjects
Study subjects were total 120 university students. Their average age was 21.94 years in male and 21.11 years in female. Their sex was 48 males and 72 females. In the results of university years among them, 1 years was 41 students, 2 years was 34 students, 3 years was 29 students, and 4 years was 16 students. In the results of un-contact lecture experience among them, a total of 25 subjects had 0 to 6 months experience, a total of 75 subjects had 6 to 12 months experience, and a total of 20 subjects had 12 months above experience (Table 1).
3.2 The results of variables
As the results of bedtime procrastination, sleep disorder, and depression showed as follows (Table 2). As the results of bedtime procrastination, the average value showed 30.18 points and the range of values showed 33 points from 12 to 45 points. As the results of sleep disorder, the average value showed 34.82 points and the range of values 40 points showed from 17 to 57 points.
As the results of depression, in the case of general symptom, the average value showed 5.18 points and the range of values 6 points showed from 2 to 8 points and in the case of psychological symptom, the average value showed 24.23 points and the range of values 27 points showed from 10 to 37 points. In the case of physiological symptom, the average value showed 15.05 points and the range of values 20 points showed from 8 to 28 points and in the case of total score, the average value showed 44.47 points and the range of values 47 points showed from 23 to 70 points.
Table 1.General characteristics of study subjects (n=120)
Characteristics Items Mean±S.D
Age (years) `Male 21.94±1.98
Female 21.11±1.62
Sex (n, %) Male 48 (40.00)
Female 72 (60.00)
University years (n, %)
1 41 (34.17)
2 34 (28.34)
3 29(24.17)
4 16 (13.33)
Un-contact lecture experience (months)
0-6 25 (20.83)
6-12 75 (62.50)
12 above 20 (16.67)
Table 2Results of variables
Variables Mean S.D Min Max Range
Bedtime procrastination (points) 30.18 6.14 12.00 45.00 33.00
Sleep disorder (points) 34.82 7.68 17.00 57.00 40.00
Depression (points)
General symptom 5.19 1.28 2.00 8.00 6.00
Psychological symptom 24.23 6.04 10.00 37.00 27.00 Physiological symptom 15.05 2.83 8.00 28.00 20.00
Total scores 44.47 9.38 23.00 70.00 47.00
Table 3Results of correlation analysis between variables
Variables 1 2 3 4 5 6
1. Bedtime procrastination 1
2. Sleep disorder .447** 1
3. Depression (General symptom) .422** .436** 1
4. Depression (Psychological symptom) .389** .446** .568** 1
5. Depression (Physiological symptom) .294** .576** .432** .480** 1
6. Depression (total scores) .428** .582** .678** .917** .777** 1
**p<0.01
3.3 The results of correlation analysis between variables
According to the purpose of this study, to verify the relationship between bedtime procrastination and sleep disorder, and depression according to the purpose of this study before the confirmatory factor analysis, correlation analysis was performed. The results of these showed as follows (Table 3). According to the table 3, all the results of correlation analysis showed the positive correlation among all of the variables (p<.01). Thus, the positive correlation between bedtime procrastination and sleep disorder, and depression was confirmed.
4. Discussion
In the condition of COVID-19 pandemic, as the social distancing is an effective measureto reduce the risk of infection by up to 99%, these is essentially recommended and applies to epidemic precautions that must be done. However, if social distancing is sustained, it induces major changes in daily life, such as changes in daily patterns and work, reducing interaction with others and limiting social participations. As a results, the level of psychological depression is increased, and this is induced which increases psychological problems and threatens the mental health of the individuals [28]. In the previous studies, depression is an important factor to induce occurrence of the sleep problems and these studies demonstrated the closely relationship between the depression and sleep problems. Additionally, O’Leary et al. [7] reported that the sleep problems is important as a factor to cause the depression. Accordingly, this study was performed to analyze the correlation among the bedtime procrastination, sleep disorder, and depression of university students during the COVID-19 pandemic.
As the results, during the COVID-19 pandemic, the positive correlation showed among the bedtime procrastination, sleep disorder, and depression of university students. These results could be interpreted as increasing the sleep disorder as university students’ bedtime procrastinationincreases. Specifically, according to the bedtime procrastination scale, problems are classified by a cut off value of 33 points. As the results of bedtime procrastination of university students during COVID-19 pandemic in this study, the average points showed at 30.18 points, and the range of points showed the 33 points. Accordingly, in this study, the study results indicated that the 26.6% of all study subjects have problems with bedtime procrastination due to the COVID-19 pandemic.
From these results, although it does not correspond to a score of 33 points or higher, it is determined that the number of subjects with the problems related in bedtime procrastination could be further increased considering the number of distributed potential subjects close to the cut off value.
Under the application of social distancing in the condition of COVID-19 pandemic recently, university students had to adapt to an environment and situation they had never experienced before [29]. Especially, through the application of un-contact lectures, the restriction of university life, reduction and disconnection of social participation and interpersonal relationships occurred
and then, the university students’ anxiety and stress levels significantly increased [30]. The study by Conroy et al. [31] also reported that the COVID-19 pandemic contribute the university students to cause the psychological problems and change the sleep pattern negatively by changing the life style. Actually, in the study by Conroy et al.[31], they reported that most of the subjects (60%) were exposed themselves to more screen time using a smartphone or tablet around bedtime, and of those 37% were searching the news or social media related in COVID-19 for 30 minutes to 2 hours before bedtime.
Cellini et al. [32] also reported that the changes in lifestyle pattern of university students during the COVID-19 pandemic increase bedtime procrastination such as increasing the use of digital media and the phenomenon not to fall in sleep. Accordingly, they reported that these problems lead university students to changenegatively in the sleep time and sleep and wake pattern. Chung et al. [33] reported that these problems occurring the sleep significantly deteriorated quality of sleep. Kroese et al.[24] reported that there is aclose relationship between bedtime procrastination and sleep disorder, and they suggested that through the performance of the bedtime procrastination, sleep time is decreased insufficiently and the risk of sleep disorder such as insomnia increased. Accordingly, during the COVID-19 pandemic, this study also determinates the positive relationship between performance of bedtime procrastination and sleep disorder and the increase of bedtime procrastination lead to increase the occurrence of sleep disorder.
Therefore, during the COVID-19 pandemic, for the management about the bedtime procrastination and occurrence of sleep disorder of university students, the appropriate consideration and measures should be needed.
With these, as the results of the correlation analysis among bedtime procrastination, sleep disorder, and depression, all the results showed the positive correlation. These results indicated as increasing the level of depression as university students increase their bedtime procrastination and sleep disorder. In the Nyer et al. [34] study, they reported that there is a closely positively relationshipbetween sleep problems and depression level increased due to the increase of sleep problems and decrease of the quantity and quality of sleep.Actually, the decrease of quality of sleep and insufficient sleep time in daily life cause the psychological sensitivity and impulsivity, and hyperactivity, and these act to experience the difficulties in controlling unpleasant emotions [7]. Moreover, physiologically, these problems promote the secretion of cortisol, which is a hormone secreted in response to acute stress, and increase the level of depression along with increased psychological anxiety [35]. Based on these, we judged that the COVID-19 pandemic contribute to increase the depression level of university students due to the increase of sleep problems causing with the changes in the daily life pattern and style of them.
Generally, the COVID-19 infection had the characteristics of being easily infected by the touching a contaminant in daily life and by the droplet infection from the coughing or sneezing.
And, according to these characteristics, the infection and spread of the COVID-19 virus is occurred rapidly [36]. The reported symptoms of COVID-19 infection were various such as cough, fever, dyspnea, and muscle and joint pain related in the musculoskeletal system in the various studies, accompanied with the taste and smell blindness [1]. Moreover, thesymptoms of hypoventilation and brain dysfunction reported and the infection led to death in the severe case of infection [36]. In the various reported studies related in COVID-19 pandemic, these characteristics and social situations induced the social environment to be unstable and they reported that these conditions induce the increase of the depression level due to the increase of
social phobia level in the daily life [1][37].Weinberger et al [1] reported the increase of the depression level according to the COVID-19 pandemic and they explained that the problems such as sleep disorder are occurred throughout the daily life.
Conroy et al. [31] reported that 72% of the total 834 subjects suffered from the negative emotional and mood changes due to the COVID-19 pandemic and 84% of them were worsened in the case of above changes, and particularly, the depression level was increased. Moreover, Greenberg et al. [38] explained these psychological changes as the “Moral Injury” and they reported that the depression level significantly increased by increasingthe social phobia and uncertainty related in the life in the COVID-19 pandemic due tothe responding to continued life in anxiety about being exposed to the infection and being able to spread to others. Generally, depression is an important indicator indicating the level of mental health and sleep and depression are two-way, close relationships that affect each other. Additionally, sleep disorder is considered to be an important factor that can have a negative effect on both side of depression. Accordingly, in the COVID-19 pandemic, based on these study’s results, the active managements and measures should be needed for the university students suffering from the various problems and multifaceted and detailed analysis are necessary for the various factors affecting to the depression, bedtime procrastination, and sleep.
University students develop the important abilities and qualitiesto grow as a member of society throughout the important university years of adulthood. In these time, their physical and psychological health impacts not only on individuals but also on their society importantly and they adapt to their lifestyle and environmental changes, and are developed their lifestyle in healthy way [39]. Among the various activities of daily living, sleep is an important basic need that account for 30% of the half of the lifetime, and avital activity which is need to maintain the life by restoring physical and mental health [40-42]. Accordingly, in this study, the analysis about the correlation among the bedtime procrastination, sleep disorder and depression of university student during the COVID-19 pandemic has the clinical significance.
Study limitations as follows. First, this study was performed only to analyze the correlation among the variables, so the results of this study was limited only to confirming the relationship among the various. Thus, the further studies should be needed to analyze the casual relationship among the variables. Second, the further analysis of various factors causingthe bedtime procrastination, sleep disorder, and depression during the COVID-19 pandemic and the influenced variables should be analyzed. Based on these analysis, the appropriate approach and measures should be considered to contribute the positive changes in the bedtime procrastination, sleep disorder, and depression level of university students during the COVID-19 pandemic.
5. Conclusions
The purpose of this study was to provide the basic information about the correlation analysis among the bedtime procrastination, sleep disorder, and depression of university students during COVID-19 pandemic. As the results of these, the positive correlation among all of the variables.
The COVID-19 pandemic contributes as a factor to increase the bedtime procrastination, induce the sleep disorder and cause the depression among university students. Thus, in the daily life of university students, these consideration should be needed and the multi-faceted and in-depth analysis should be performed about these.
References
[1] Weinberger, D. M., Chen, J., Cohen, T., Crawford, F. W., Mostashari, F., Olson, D., ...&Viboud, C. (2020). Estimation of excess deaths associated with the COVID-19 pandemic in the United States, March to May 2020. JAMA Internal Medicine, 180(10), 1336-1344.
[2] Choi, S. & Ki, M. (2020). Estimating the reproductive number and the outbreak size of COVID-19 in Korea. Epidemiology and health,42, 1-10.
[3] Son, S. M., Jo, E. S., & Choi, S. J. (2021). Changes in major commitment and satisfaction of 1st and 2nd grades university students in health-related departments through the application of un-contact lectures during COVID-19 pandemic. Journal of the Korean Applied Science and Technology, 38(2), 389-398.
[4] Son, S. M. & Hong, H. N. (2021). Changes in the job commitment and social interaction anxiety among occupational therapist working in long term care hospital through the COVID-19 vaccination. Annals of the Romanian Society for Cell Biology, 25(5), 5691- 5701.
[5] Kim, S. Y. (2020). A convergence study of stress caused by the epidemic of COVID-19, quality of life and positive psychological capital. Journal of the Korea Convergence Society, 11(6), 423-431.
[6] Dishman, R. K., Nakamura, Y., Garcia, M. E., Thompson, R. W., Dunn, A. L., & Blair, S.
N. (2000). Heart rate variability, trait anxiety, and perceived stress among physically fit men and women. International Journal of Psychophysiology, 37(2), 121-133.
[7] O’Leary, K., Bylsma, L. M., &Rottenberg, J. (2017). Why might poor sleep quality lead to depression? A role for emotion regulation. Cognition and Emotion, 31(8), 1698-1706.
[8] Rottenberg, J. (2017). Emotions in depression: What do we really know?.Annual Review of Clinical Psychology, 13, 241-263.
[9] Pilcher, J. J., Ginter, D. R., &Sadowsky, B. (1997). Sleep quality versus sleep quantity:
relationships between sleep and measures of health, well-being and sleepiness in college students. Journal of Psychosomatic Research, 42(6), 583-596.
[10] Chou, C., Condron, L., &Belland, J. C. (2005). A review of the research on Internet addiction. Educational Psychology Review, 17(4), 363-388.
[11] Kim M. J. (2012). Measurement of nursing students’ sleep using by an automated wireless sleep tracker and subjective sleep scales. Journal of Korean Academy of Fundamentals of Nursing. 19(4): 434-43.
[12] Schreier, N., Huss, A., &Röösli, M. (2006). The prevalence of symptoms attributed to electromagnetic field exposure: A cross-sectional representative survey in Switzerland.
Sozial-und Präventivmedizin, 51(4), 202-209.
[13] Lee, H. G. (2008). Exploration the predicting variables affecting the addictive mobile phone use. Korean Journal of Social and Personality Psychology, 22(1), 133-157.
[14] Zou, Y., Xia, N., Zou, Y., Chen, Z., & Wen, Y. (2019). Smartphone addiction may be
associated with adolescent hypertension: a cross-sectional study among junior school students in China. BMC pediatrics, 19(1), 1-8.
[15] Grandner, M. A., Gallagher, R. A. L., &Gooneratne, N. S. (2013). The use of technology at night: impact on sleep and health. Journal of Clinical Sleep Medicine, 9(12), 1301- 1302.
[16] Lee, J. E. & Park, H. R. (2003). Body-related attitude, self-esteem and eating attitude in undergraduate students. Journal of Korean Academy of Psychiatric and Mental Health Nursing, 12, 603-611.
[17] Wang, L., Xu, H., Zhang, X., & Fang, P. (2017). The relationship between emotion regulation strategies and job search behavior among fourth-year university students.
Journal of Adolescence, 59, 139-147.
[18] Jung, S. H. & Park, J. (2013). Effect of life stress on the sleeping disorder of university student. The Journal of the Korea Institute of Electronic Communication Sciences, 8(2), 345-353.
[19] Sung, M. J. & Chang, K. J. (2006). Correlations among life stress, dietary behaviors and food choice of college students. Journal of the East Asian Society of Dietary Life, 16(6), 655-662.
[20] Kim, G. H. & Yoon, H. S. (2013). Factors influencing sleep quality in nursing students and non nursing students. Journal of Korean Academy of Psychiatric and Mental Health Nursing, 22(4), 320-329.
[21] Kim, Y. S. (2017). Factors influencing quality of sleep in nursing students. Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology, 7(6), 473-483.
[22] Faul, F., Erdfelder, E., Lang, A. G., & Buchner, A. (2007). G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences.
Behavior Research Methods, 39, 175-191.
[23] Wilson, F. R., Pan, W., &Schumsk, D. A. (2012). Recalculation of the critical value for Lawshe’s content validity ratio. Measurement and Evaluation in Counseling and Development, 45(3), 197-210.
[24] Kroese, F. M., Nauts, S., Kamphorst, B. A., Anderson, J. H., & de Ridder, D. (2016).
Bedtime procrastination: A behavioral perspective on sleep insufficiency.
Procrastination, Health, and Well-being, 2016, 93-116.
[25] Oh, J. J., Song, M. S., & Kim, S. M. (1998). Development and validation of Korean sleep scale A. Journal of Korean Academy of Nursing, 28(3), 563-572.
[26] Zung, W. W. (1965). A self-rating depression scale. Archives of General Psychiatry, 12(1), 63-70.
[27] Chung, C. Y. & Kim, D. H. (2013). Are anxiety and depression distint?: Exploratory factor analysis of Zung’s self-rating anxiety and depression scale. Korean Journal of Biological Psychiatry, 20, 21-27.
[28] Koo, J. R., Cook, A. R., Park, M., Sun, Y., Sun, H., Lim, J. T., ...& Dickens, B. L. (2020).
Interventions to mitigate early spread of SARS-CoV-2 in Singapore: A modelling study.
The Lancet Infectious Diseases, 20(6), 678-688.
[29] Oosterhoff, B., Palmer, C. A., Wilson, J., & Shook, N. (2020). Adolescents' motivations to engage in social distancing during the COVID-19 pandemic: Associations with mental and social health. Journal of Adolescent Health, 67(2), 179-185.
[30] Kim, N. E. (2011). The relationships among stress, resilience, and quality of life in college students. Journal of Adolescent Welfare, 13(4), 1-19.
[31] Conroy, D. A., Hadler, N. L., Cho, E., Moreira, A., MacKenzie, C., Swanson, L. M., Burgess, H. J., Arnedt, J. T., & Goldstein, C. A. (2021). The effects of COVID-19 stay-at- home order on sleep, health, and working patterns: A survey study of US health care workers. Journal of Clinical Sleep Medicine, 17(2), 185-191.
[32] Cellini, N, Canale, N., Miori, G., & Costa, S. (2020). Changes in sleep pattern, sense of time and digital media use during COVID-19 lockdown in Italy. Journal of Sleep Research, 29(4), e13074.
[33] Chung, S. J., An, H., & Suh, S. (2020). What do people do before going to bed? A study of bedtime procrastination using time use surveys. Sleep, 43(4), zsz267.
[34] Nyer, M., Farabaugh, A., Fehling, K., Soskin, D., Holt, D., Papakostas, G. I., ...&Mischoulon, D. (2013). Relationship between sleep disturbance and depression, anxiety, and functioning in college students. Depression and Anxiety, 30(9), 873-880.
[35] Hanson, M. D. & Chen, E. (2010). Daily stress, cortisol, and sleep: the moderating role of childhood psychosocial environments. Health Psychology, 29(4), 394.
[36] Jones, L., Walsh, K., Willcox, M. Morgan, P., & Nichols, J. (2020). The COVID-19 pandemic:
Important considerations for contact lens practitioners. Contact Lens and Anterior Eye, 43, 196-203.
[37] Gao, J., Zheng, P., Jia, Y., Chen, H., Mao, Y., Chen, S., Wang, Y., & Fu, H. Dai, J.
(2020). Mental health problems and social media exposure during COVID-19 outbreak.
Plos one, 15(4), e0231924.
[38] Greenberg, N., Docherty, M., Gnanapragasam, S., &Wessely, S. (2020). Managing mental health challenges faced by health care workers during COVID-19 pandemic, BMJ, 368, m1211.
[39] Park, N. S. (2011). Development of comprehensive health promotion policies for university students. Korean Journal of Health Education and Promotion, 28(5), 17-34.
[40] Suh, S., Ellis, R. J., Sollers III, J. J., Thayer, J. F., Yang, H. C., & Emery, C. F. (2013).
The effect of anxiety on heart rate variability, depression, and sleep in chronic obstructive pulmonary disease. Journal of Psychosomatic Research, 74(5), 407-413.
[41] Suk, H. J., Na, K. E., & Hong, S. H. (2014). Difference in sleep circadian rhythm and sleep quality between normal-weight and obese group. Journal of Korean Biological Nursing Science, 16(4), 309-317, 2014.
[42] Vandeputte, M. & de Weerd, A. (2003). Sleep disorders and depressive feelings: A global survey with the Beck depression scale. Sleep Medicine, 4(4), 343-345.
