Circadian Preferences, Sleep Quality and Sleep Patterns, Personality, Academic Motivation and Academic Achievement of university students

Learning and Individual Differences 32 (2014) 184–192

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Learning and Individual Differences journal homepage: www.elsevier.com/locate/lindif

Circadian Preferences, Sleep Quality and Sleep Patterns, Personality, Academic Motivation and Academic Achievement of university students İsmail Önder a,⁎, Şenol Beşoluk a, Murat İskender b, Ercan Masal c, Eda Demirhan a a b c

Faculty of Education, Department of Science Education, Sakarya University, Turkey Faculty of Education, Department of Psychological Counseling and Guidance, Sakarya University, Turkey Faculty of Education, Department of Secondary Science and Mathematics Education, Sakarya University, Turkey

a r t i c l e

i n f o

Article history: Received 18 July 2013 Received in revised form 28 December 2013 Accepted 21 February 2014 Keywords: Morningness–Eveningness Preference Sleep Personality Motivation Cumulative Grade Point Average

a b s t r a c t In the current study, the relationships among Circadian Preferences, Sleep Quality and Sleep Patterns, Personality, Academic Motivation and the Academic Achievement of university students are examined. 1343 university students (62.8% females and 37.2% males) participated in the study. Data was gathered from each participant using a Morningness–Eveningness Questionnaire (MEQ), Pittsburgh Sleep Quality Index (PSQI), Adjective Based Personality Test (ABPT), Academic Motivation Scale (AMS-C) and Descriptive Questionnaire, completed voluntarily. A regression analysis model revealed the following predictors: corrected Midpoint of Sleep, Academic Motivation, Social Jetlag, Conscientiousness, Intrinsic Motivation toward Accomplishment, Intrinsic Motivation to Experience Stimulation and Neuroticism, explaining 15.1% of the variance of Cumulative Grade Point Average (CGPA). Meanwhile, CGPA scores of earlier chronotypes were higher than those of later chronotypes. Corrected Midpoint of Sleep, global PSQI, Conscientiousness, Extrinsic Motivation-External Regulation and Intrinsic Motivation to Experience Stimulation, Social Jetlag, Extraversion, Intrinsic Motivation toward Accomplishment and Intrinsic Motivation to Know emerged as significant predictors of MEQ explaining the 26.7% of the variance. Conscientiousness, CGPA, Openness to Experience, Neuroticism and Social Jetlag were the significant predictors of AMS-C explaining 14.7% of the variance in Academic Motivation. Analysis in Sleep Quality presented that 13.4% of the variance was explained by chronotype preference, Average Sleep Length (ASL), Neuroticism, corrected Midpoint of Sleep and Extraversion. Moreover, in the female sample both Sleep Quality and Academic Motivation of morning type students were better than those of evening types and those of neither type. Meanwhile regression analysis shows that in all Personality traits Academic Motivation and sub-domains of Academic Motivation are significant predictors; and in some Personality traits, ASL, circadian typology and Academic Achievement emerged as significant predictors. These results suggested that Circadian Preferences, Sleep Quality and Sleep Patterns, Personality and Academic Motivation were interrelated and had a significant effect on Academic Achievement. © 2014 Elsevier Inc. All rights reserved.

1. Introduction 1.1. Chronotype The concept of morningness–eveningness (M–E) shows interindividual differences in academic performance (Díaz-Morales & Escribano, 2013; Roeser, Schlarb, & Kübler, 2013), can be derived from

⁎ Corresponding author at: Sakarya Üniversitesi Eğitim Fakültesi, 54300 Hendek, Sakarya, Turkey. Tel.: +90 2642957169; fax: +90 2642957183. E-mail address: [email protected] (İ. Önder).

http://dx.doi.org/10.1016/j.lindif.2014.02.003 1041-6080/© 2014 Elsevier Inc. All rights reserved.

physiological parameters, e.g., concentration of melatonin or cortisol, core body temperature, sleep–wake cycle (Adan et al., 2012; Randler, 2008; Randler & Schaal, 2010; Waterhouse, Fukuda, & Morita, 2012) and is usually measured in a continuous scale where individuals depending on their position in the continuum may be morning type (MT), neither type (NT) or evening type (ET) (Natale & Cicogna, 2002). Circadian Preference is partly genetic (Adan et al., 2012) and is also affected by other factors, including age, gender and cultural, social, environmental, technological and biological variables (Adan et al., 2012; Randler, 2008, 2011; Randler, Vollmer, Beşoluk, Önder, & Horzum, 2013; Vollmer, Michel, & Randler, 2012). Meanwhile, M–E is related to variables such as preferred bed/rise times, Midpoint of Sleep, and preferred time for

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mental and physical activity (Adan et al., 2012). MT individuals feel and perform best in the morning hours (Valdez, Reilly, & Waterhouse, 2008) while ET individuals perform and feel best later on in the day (Martin & Martin, 2013). However, due to common social demands ET individuals have to keep up with morning activities and duties when their chronotype is in asynchrony with their preferred time of day (DíazMorales & Escribano, 2013). This asynchrony between social and biological rhythms (Social Jetlag) causes ET individuals to sleep less on work/ school days (Tzischinsky & Shochat, 2011; Wittmann, Dinich, Merrow, & Roenneberg, 2006) and may affect their pattern and quality of sleep. Furthermore, MT individuals who have to work or study at later times of the day may be faced with similar problems. The times at which individuals rise and retire are different on work/school days and free days because of these social demands. As such Roenneberg, Wirz-Justice, and Merrow (2003) and Roenneberg et al. (2004) suggest determining chronotype by the use of corrected Midpoint of Sleep in free days (MSFsc). 1.2. Sleep, chronotype and Academic Achievement Sleep, as an important human biological process, has effects on human behavior, psychology and health (Megdal & Schernhammer, 2007). Research indicates that insufficient sleep, poor quality sleep or unusual sleep habits have a negative influence on individuals' physical and mental health, performance and activity (Preišegolavičiūtė, Leskauskas, & Adomaitienė, 2010; Valdez et al., 2008). Although sleep problems have such negative effects, insufficient sleep or poor quality sleep is common among university students (Carney, Edinger, Meyer, Lindman, & Istre, 2006; Suen, Hon, & Tam, 2008). Meanwhile, Gomes, Tavares, and de Azevedo (2011) indicated that self-reported Sleep Quality and self-reported frequency of sufficient sleep together with some other variables were among the main predictors of academic performance. On the other hand, Eliasson, Eliasson, King, Gould, and Eliasson (2002) reported no correlation between sleep length and academic performance. Chronotype influences the quality of sleep–wake cycle and sleep deprivation thus influence the learning of university students (Onyper, Thacher, Gilbert, & Gradess, 2012). Several studies have found that ET students have poorer Sleep Quality than MT and/ or NT ones (Lima, Varela, Silveira, Parente, & Araujo, 2010; Vardar, Vardar, Molla, Kaynak, & Ersoz, 2008). Meanwhile, Borisenkov, Perminova, and Kosova (2010) indicated that the effect of chronotype was stronger than that of sleep duration on students' achievement. Students that easily wake up in the morning and are therefore active at earlier times of day were found to perform better in school and exams than ET students (Beşoluk, 2011; Beşoluk, Önder, & Deveci, 2011; Curcio, Ferrara, & De Gennaro, 2006; Önder, Horzum, & Beşoluk, 2012; Preckel, Lipnevich, Schneider, & Roberts, 2011). Similarly, MT students were found to have higher grade point averages (GPA) and fewer school-related problems compared to ET students (Vollmer, Schaal, Hummel & Randler, 2011; Wolfson & Carskadon, 1998). 1.3. Motivation, chronotype and Academic Achievement Apart from chronotype and sleep-related variables, Motivation also affects Academic Achievement and students' performance in school. Roeser et al. (2013) indicated that learning and achievement Motivation may explain the link between chronotype and Academic Achievement. Since ET individuals are less alert in the early hours of the day, they may have difficulty in meeting the demands of instructors and therefore have lower motivation to learn and achieve. Moreover, ET individuals have difficulty in waking up early in the morning and have more sleepiness, so they may go to school with low motivation. On the other hand, the academic performance of MT students might be higher since they are more alert, they have less sleep related problems and better Sleep

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Quality (Escribano, Díaz-Morales, Delgado, & Collado, 2012), and they may have higher motivation to learn and achieve (Roeser et al., 2013).

1.4. Personality, sleep, chronotype and Academic Achievement Previous research has investigated the association of Big Five Personality traits with sleep–wake variables, chronotype, and academic performance. Controversial results were reported with respect to the association between sleep duration and Personality variables. Soehner, Kennedy, and Monk (2007) found no correlation between sleep duration and Personality variables, but some others have found a correlation (Gau, 2000; Randler, 2008). With respect to Personality and chronotype, Conscientiousness was reported as the best predictor of morningness (Adan et al., 2012). Meanwhile, positive relationships were found between Agreeableness and morningness (DeYoung, Hasher, Djikic, Criger, & Peterson, 2007; Randler, 2008), and Neuroticism and eveningness (Randler, 2008; Tonetti, Fabbri, & Natale, 2009). With respect to Personality variables and academic performance, Conscientiousness was reported as the most strongly related Personality variable with academic performance (ChamorroPremuzic & Furnham, 2005; Gray & Watson, 2002; O'Connor & Paunonen, 2007) and a positive association was reported between Openness to Experience and academic performance (ChamorroPremuzic & Furnham, 2005; O'Connor & Paunonen, 2007). The association between Conscientiousness and academic performance is explained by Motivation since conscientious students might be more motivated to perform well academically (Chamorro-Premuzic & Furnham, 2005). Moreover, several studies have shown that Intrinsic Motivation, Extrinsic Motivation and Amotivation are related with Personality traits (Clark & Schroth, 2010; Komarraju & Karau, 2005; Komarraju, Karau, & Schmeck, 2009).

1.5. Aims of the study Many factors affect Academic Achievement, and some of those are related to individual differences. The ability to predict individual differences that affect Academic Achievement may have valuable educational applications. We hypothesized that the chronotype/Circadian Preference, Academic Motivation, Personality and sleep variables are associated with Academic Achievement. However no study was found in the literature that investigates the relationships among these variables concurrently. Therefore the main purpose of the present study is to assess associations among chronotype/Circadian Preferences, Sleep Quality and Sleep Patterns, Personality, Academic Motivation and Academic Achievement for the first time in a Turkish university population, and to determine whether chronotype/Circadian Preferences, Sleep Quality and Sleep Patterns, Personality, and Academic Motivation are predictors of Academic Achievement, and if so how Academic Achievement scores change with respect to these variables. Meanwhile, we also hypothesized that Circadian Preference is associated with Academic Motivation, Personality and sleep variables. Therefore we have also investigated whether Circadian Preference predicts Academic Motivation, Personality and sleep variables and if so, how the scores on these variables change with respect to chronotype.

2. Method In the current study a survey methodology was used. Simple random sampling was used in selecting university students that will participate in the study. Students completed the data-collecting tools anonymously and voluntarily.

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2.1. Sample Data was collected from 1343 university students (62.8% females and 37.2% males) enrolled in the departments of science education, social studies education, primary education, Turkish language education, mathematics education, special education, computer education and instructional technology, and psychological counseling and guidance. The sample consisted of sophomore, junior, and senior students from each department and the proportion of each grade level reflects the proportion of each grade level in the population. Freshmen students were not included in the sample because they can have some adaptation problems which could affect the results. The ages of the students ranged from 18 to 34, with a mean of 21.01 years and a standard deviation of 1.78 years. The descriptive data regarding the sample were presented in Appendix 1.

2.2. Instruments 2.2.1. Morningness–Eveningness Questionnaire (MEQ) The MEQ, devised by Horne and Östberg (1976), consists of 19 mixed-format questions regarding habitual rising and bed times, the preferred times for physical and mental activities, and subjective alertness. MEQ yields scores ranging from 16 to 86 where high scores indicate morningness. MEQ was adapted into Turkish by Pündük, Gür, and Ercan (2005) and they have reported that the MEQ's reliability is high, with a Cronbach's alpha value of .812. The internal consistency coefficient of the scale in the current study was .761.

2.2.2. Pittsburgh Sleep Quality Index (PSQI) The PSQI is a 19-item self-rating tool designed to measure Sleep Quality and pattern of sleep over the past month, developed by Buysse, Reynolds, Monk, Berman, and Kupfer (1989). The items that should be rated by the participant's bed partner or roommate were excluded in this study. The PSQI contains seven components: subjective Sleep Quality, sleep-onset latency, sleep duration, sleep efficiency, sleep disturbances, use of sleeping medications, and daytime dysfunction. Each component's score can range from 0 to 3 and the sum of those component scores gives a global Sleep Quality score ranging from 0 to 21. Scores higher than 5 in the global PSQI indicate poor Sleep Quality (Buysse et al., 1989). The scale was adapted into Turkish by Ağargün, Kara, and Anlar (1996) and they reported the internal consistency coefficient of the scale as .804; in the current study it was .781.

2.2.3. Adjective Based Personality Test (ABPT) The ABPT was developed by Bacanlı, İlhan, and Aslan (2009), based on the Five Factor Model of Personality. The instrument contains 40 adjective pairs with a 7 point Likert-type scale and five subscales; Neuroticism, Extraversion, Openness to Experience, Agreeableness and Conscientiousness. The internal consistency coefficients and test–retest reliabilities of the five sub-scales reported by the original authors range between .73 and .89. Both construct and concurrent validity results were significant. The internal consistency coefficients of the five sub-scales in the current study ranged from .712 to .874.

2.2.4. Academic Motivation Scale (AMS-C) The AMS-C was developed by Vallerand et al. (1992) and contains seven sub-scales: Intrinsic Motivation (IM) to Know, IM toward Accomplishment, IM to Experience Stimulation, Extrinsic Motivation (EM) Identified, EM Introjected, EM External Regulation, and Amotivation. The AMS-C contains 28 items and the scores range from −18 to +18.

The internal consistency coefficients reported by Vallerand et al. (1992) vary from .62 to .86. The AMS-C was adapted into Turkish by Demir (2008) and the internal consistency coefficients of the seven sub-scales ranged from .70 to .80 in her study. The internal consistency coefficients of seven sub-scales in the current study range between .789 and .854. 2.2.5. Descriptive questionnaire A demographic questionnaire was used to gather data on the participants' gender, department, grade, age, and retiring and rising times (both on weekdays and on weekends). Corrected Midpoint of Sleep in Free days (MSFsc: as another indicator of chronotype), Average Sleep Length (ASL) and Social Jetlag variables were calculated from rise and retire times. 2.2.6. Statistical analysis In the study the students' Cumulative Grade Point Averages (CGPAs) were used as an indicator of overall Academic Achievement. Therefore the cumulative grade point averages of students from various majors with mean (M) and standard deviation (SD) of each major and grade level were obtained from the registry, with the students' permission. The mean and standard deviation scores obtained from the registry were used to compute t-scores in order to standardize CGPA data [t-score = (((Xi − M) ∕ SD) ∗ 10) + 50; Xi: CGPA of ith individual, M: mean CGPA of students with same grade and department with that of ith individual; and SD: standard deviation of CGPA scores obtained from students with same grade and department with that of ith individual]. The t-scores were used as data in all CGPA analyses. Possible associations among Academic Achievement, Circadian Preferences, Sleep Quality and Sleep Patterns, Personality and Academic Motivation variables were tested by Pearson product–moment correlation coefficients. Additionally, a series of simultaneous regression analyses were conducted to investigate the relationship among Circadian Preferences, Sleep Quality and Sleep Patterns, Personality, Academic Motivation and Academic Achievement in a more systematic manner. Stepwise regression detects the model which explains the highest amount of variance in the data with the smallest number of predictors. Two-way analysis of covariance (ANCOVA) was conducted to evaluate the effect of chronotype (MSFsc) and Sleep Quality [good (PSQI score ≤ 5) and poor (PSQI score N 5)] on CGPA after adjusting for age and Motivation (AMS-C). Meanwhile, in order to control the effect of gender this analysis was performed for males and females separately. MSFsc was calculated with the formula described by Roenneberg et al. (2004) [MSFSC =MSF − 0.5 ∗ (SDF − (5 ∗ SDW + 2 ∗ SDF) ∕ 7)]; MSF: Midpoint of Sleep on Free days, SDF: Sleep duration on free days, and SDW: Sleep duration on work days]. Midpoint of Sleep on Weekends was used instead of Midpoint of Sleep in free days in the formula, because our qualitative studies in university students showed that they perceive weekends as free days. For the categorical analysis, MSFSC was divided into two groups (≤median and Nmedian; earlier and later chronotypes) as indicated in Genzel et al. (2013). ASL was calculated with the formula described by Juda, Vetter, and Roenneberg (2013) [ASL = (5 ∗ SDW + 2 ∗ SDF) ∕ 7] and Social Jetlag was calculated with the formula presented by Roenneberg, Allebrandt, Merrow, and Vetter (2012) [Social Jetlag = MSF − MSW; MSW: mid-sleep on work days]. Oneway ANCOVA was conducted to evaluate the effect of chronotype preference (MEQ based; MT, NT, ET) on variables (Sleep Quality and Academic Motivation) controlling the variance of age. Meanwhile, in order to control the effect of gender this analysis was performed for males and females separately. In this analysis three classes of chronotype preference were used: ET (MEQ score 16–41), NT (MEQ score 42–58), and MT (MEQ score 59–86). Academic Motivation scores were calculated with the formula described by Guay, Mageau, and Vallerand (2003) [self-determination index = (2 × (IM to Know + IM to accomplish +

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IM to Experience Stimulation) ∕ 3 + Identified Regulation) − ((Introjected Regulation + External Regulation) ∕ 2 + 2 × Amotivation)]. The level of significance was set to .05 corrected

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according to the Bonferroni procedure for multiple testing (to hold the alpha level at ≤ .05). The software package PASW Statistics 18.0 was used for all statistical analyses.

Table 1 Regression results. Variable

Predictor

Beta

R2

Change in R2

Significance

CGPA

MSFsc AMS-C Social Jetlag Conscientiousness Intrinsic motivation toward accomplishment Intrinsic motivation to experience stimulation Neuroticism MSFsc Global PSQI Conscientiousness Extrinsic motivation external regulation Intrinsic motivation to experience stimulation Social Jetlag Extroversion Intrinsic motivation toward accomplishment Intrinsic motivation to know Conscientiousness CGPA Openness to Experience Neuroticism Social Jetlag Openness to Experience CGPA Conscientiousness Agreeableness MSFsc Neuroticism Conscientiousness MSFsc CGPA Openness to Experience MEQ Agreeableness Conscientiousness CGPA Agreeableness Neuroticism MEQ ASL Neuroticism MSFsc Extroversion Intrinsic motivation to know AMS-C AMS-C MEQ ASL Intrinsic motivation toward accomplishment Extrinsic motivation identified AMS-C MEQ Intrinsic motivation toward accomplishment CGPA Intrinsic motivation to experience stimulation Extrinsic motivation introjected ASL Global PSQI Global PSQI ASL AMS-C CGPA Intrinsic motivation toward accomplishment Intrinsic motivation to know AMS-C Intrinsic motivation to know

−.194 .166 −.115 .100 .161 −.110 .059 −.403 −.153 .166 −.136 .122 .067 −.070 −.103 .084 .149 .197 .185 −.089 .067 .259 .156 .155 −.144 .076 −.061 .211 .132 .123 .120 −.074 −.077 −.116 −.135 −.119 .073 −.176 −.241 .182 .119 −.069 .126 .114 .201 .098 −.080 −.120 .116 .204 .143 .144 .115 −.141 .101 −.074 −.060 .195 .073 −.091 .070 .121 −.105 .168 .162

.064 .109 .122 .135 .142 .148 .151 .191 .213 .229 .242 .253 .258 .261 .264 .267 .080 .108 .134 .143 .147 .074 .096 .104 .115 .120 .124 .052 .072 .086 .092 .096 .100 .042 .057 .069 .074 .044 .088 .119 .130 .134 .041 .048 .052 .062 .068 .073 .079 .080 .105 .123 .137 .144 .148 .152 .155 .033 .040 .046 .052 .056 .061 .077 .091

.064 .044 .014 .013 .007 .006 .003 .191 .022 .016 .013 .011 .004 .003 .003 .003 .080 .028 .026 .008 .004 .074 .022 .008 .011 .005 .004 .052 .020 .014 .006 .005 .004 .042 .016 .013 .005 .044 .043 .031 .011 .005 .041 .007 .052 .011 .006 .005 .006 .080 .025 .018 .013 .008 .004 .004 .003 .033 .007 .006 .006 .004 .005 .077 .014

F(7, 1106) = 28.197, p b .001

MEQ

Academic Motivation

AMS-C

Intrinsic Motivation

Extrinsic Motivation

Amotivation

Sleep Quality (Global PSQI)

Big Five Personality Traits

Extroversion Agreeableness

Conscientiousness

Neuroticism

Openness to Experience

F(9, 1104) = 44.582, p b .001

F(5, 1108) = 38.246, p b .001

F(6, 1107) = 26.123, p b .001

F(6, 1107) = 20.504, p b .001

F(4, 1109) = 23.079, p b .001

F(5, 1108) = 34.417, p b .001

F(2, 1111) = 27.981, p b .001 F(5, 1108) = 19.077, p b .001

F(8, 1105) = 25.333, p b .001

F(6, 1107) = 11.901, p b .001

F(2, 1111) = 55.808, p b .001

MEQ: Morningness–Eveningness Questionnaire; AMS-C: Self-determination Index; Global PSQI: Global Pittsburgh Sleep Quality Index; CGPA: Cumulative Grade Point Average; MSFsc: Corrected mid-sleep time on free days; ASL: Average Sleep Length.

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3. Results 3.1. Preliminary analysis The distributions of the variables [CGPA, Circadian Preferences (MEQ), Sleep Quality (PSQI), Sleep Patterns (ASL, MSFSC and Social Jetlag), Personality and Academic Motivation (AMS-C and sub-domains)] were examined for normality via skewness and kurtosis (N± 1). The variables were normally distributed except the Amotivation variable (skewness = 1.56 and kurtosis = 1.97). Past research indicated that the Amotivation sub-domain often displays a skewed distribution and this non-normal distribution does not pose any problem (Gillet, Vallerand, & Rosnet, 2009). 3.2. Descriptive results The data collecting tools were completed by 1343 university students; however there were missing values in each variable and these missing values were excluded from the analysis. Therefore, full datasets for each variable were used. Group size, mean and standard deviation of MEQ, Academic Motivation, Personality variables, Sleep variables, Sleep Quality and CGPA for total sample, gender, chronotype, Sleep Quality and age are presented in Appendix 1. 3.3. Academic Achievement-related results Pearson product–moment correlations (presented in Appendix 2) among Circadian Preference, Sleep Quality, Sleep Pattern, Personality, Academic Motivation and Academic Achievement variables showed that CGPA mainly correlates positively with AMS-C, IM, EM, MEQ, Agreeableness and Conscientiousness, and negatively with MSFSC, Social Jetlag and Amotivation. A stepwise regression analysis model clarified the nature of relations, and revealed MSFSC (β = − .194), AMS-C (β = .166), Social Jetlag (β = − .115), Conscientiousness (β = .100), IM toward Accomplishment (β = .161), IM to Experience Stimulation (β = − .110) and Neuroticism (β = .059) as the predictors explaining 15.1% (R2) of the variance of CGPA (see Table 1). The effect size of the analysis was [f2 = R2 / (1 − R2)] 0.178 indicating a medium effect size. MSFSC was the main predictor of CGPA and the Sleep Quality of the sample was mainly poor, therefore in order to investigate the effect of both variables on CGPA, two-way ANCOVA was performed. ANCOVA with chronotype (earlier/later) and Sleep Quality (poor/good) as fixed factors, and age and Academic Motivation as covariates presented a significant main effect of chronotype on Academic Achievement (CGPA) in both female [F(1, 636) = 8.896, p = .003, η2 = .014] and male [F(1, 310) = 12.511, p b .001, η2 = .039] samples. The main effect of Sleep Quality andthe interaction's simple effect were not statistically significant (p N .05) in both samples. Bonferroni-corrected multiple comparison tests indicated that the CGPA scores of earlier chronotypes (female sample: adj. M = 53.86, SE = 0.49, 95% CI = 52.90–54.83; male sample: adj. M = 49.09, SE = 0.85, 95% CI = 47.41–50.76) were better than later chronotypes (female sample: adj. M = 51.49, SE = 0.62, 95% CI = 50.27–52.71; male sample: adj. M = 45.16, SE = 0.70, 95% CI = 43.79–46.54) in both samples. 3.4. Circadian Preference (MEQ)-related results On the whole, MEQ correlates positively with AMS-C, Agreeableness and Conscientiousness, and negatively with global PSQI, and ASL (correlations already presented in the previous analysis were not indicated). To clarify the nature of relations, regression analysis was conducted and it was found that 26.7% of the variance was explained by MSFSC (β = − .403), global PSQI (β = − .153),

Conscientiousness (β = .166), EM External Regulation (β = − .136), IM to Experience Stimulation (β = .122), Social Jetlag (β = .067), Extraversion (β = − .070), IM toward Accomplishment (β = − .103) and IM to Know (β = .084). The effect size of the analysis was 0.364 (f2) indicating a large effect size.

3.5. Sleep-related results Global PSQI mainly correlates positively with Neuroticism, MSFSC and Social Jetlag, and negatively with ASL. Regression analysis conducted to investigate the extent to which Circadian Preference, Sleep Patterns, Big Five traits, CGPA and Academic Motivation explained the variance in Sleep Quality presented that 13.4% of the variance was explained by MEQ (β = − .176), ASL (β = − .241), Neuroticism (β = .182), MSFSC (β = − .119) and Extraversion (β = − .069). The effect size of the analysis was 0.155 (f2) indicating a medium effect size. Since MEQ was the main predictor of Sleep Quality one-way ANCOVA was run to investigate whether Sleep Quality differs among Circadian Preferences. ANCOVA with chronotype preference (MT, NT and ET) as a fixed factor, and age as a covariate showed a significant effect of chronotype preference on Sleep Quality (global PSQI) in the female sample [F(2, 742) = 16.783, p b .001, η 2 = .043] but no effect of chronotype preference on Sleep Quality was found in the male sample (p N .05). Bonferroni-corrected multiple comparison tests conducted in the female sample indicated that the sleep qualities of MT students (adj. M = 6.39, SE = 0.22, 95% CI = 5.96–6.83) were better than both NT (adj. M = 7.14, SE = 0.13, 95% CI = 6.89–7.39) and ET (adj. M = 8.47, SE = 0.28, 95% CI = 7.92–9.02) students. Similarly, the sleep qualities of NT students were better than ET students.

3.6. Academic Motivation-related results On the whole, AMS-C correlates positively with the Big Five Personality traits (except Neuroticism). Moreover, regression analysis revealed that 14.7% of the variance in Academic Motivation (AMS-C total) was explained by Conscientiousness (β = .149), CGPA (β = .197), Openness to Experience (β = .185), Neuroticism (β = −.089), and Social Jetlag (β = .067), and the effect size was medium (f2 = 0.172). For IM, 12.4% of the variance was explained by Openness to Experience (β = .259), CGPA (β = .156), Conscientiousness (β = .155), Agreeableness (β = −.144), MSFSC (β = .076) and Neuroticism (β = − .061), and the effect size was medium (f2 = 0.142). For EM, 10.0% of the variance was explained by Conscientiousness (β = .211), MSFSC (β = .132), CGPA (β = .123), Openness to Experience (β = .120), MEQ (β = −.074) and Agreeableness (β = −.077). The effect size was small (f2 = 0.111). For Amotivation, 7.4% of the variance was explained by Conscientiousness (β = − .116), CGPA (β = − .135), Agreeableness (β = −.119) and Neuroticism (β = .073). The effect size was small (f2 = 0.079). Since sub-domains of Academic Motivation was predicted by MEQ or MSFSC, one-way ANCOVA was run to investigate whether Academic Motivation differs among Circadian Preferences. ANCOVA with chronotype preference (MT, NT and ET) as a fixed factor, and age as a covariate showed a significant effect of chronotype preference on AMS-C in the female sample [F(2, 708) = 9.645, p b .001, η2 = .027] but no effect of chronotype preference on Academic Motivation was found in male sample (p N .05). The Bonferroni-corrected multiple comparison tests conducted in the female sample indicated that the Academic Motivations of MT students (adj. M = 7.80, SE = 0.30, 95% CI = 7.20–8.40) were better than both NT (adj. M = 6.32, SE = 0.18, 95% CI = 5.97–6.67) and ET (adj. M = 6.16, SE = 0.38, 95% CI = 5.41–6.91) students. However, Academic Motivations of NT students and ET students did not differ (p N .05).

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3.7. Personality related results Agreeableness and Conscientiousness were found to correlate negatively with MSFSC and ASL. Regression analysis conducted to investigate how much of the variance in the Big Five traits was explained by Circadian Preference, Sleep Quality/Patterns, CGPA and Academic Motivation revealed that: 4.8% of the variance in Extraversion was explained by IM to Know (β = .126) and AMS-C (β = .114), and the effect size was small (f2 = 0.050). For Agreeableness, 7.9% of the variance was explained by AMS-C (β = .201), MEQ (β = .098), ASL (β = −.080), IM toward Accomplishment (β = − .120) and EM Identified (β = .116). The effect size of the analysis was small (f2 = 0.086). For Conscientiousness, 15.5% of the variance was explained by AMS-C (β = .204), MEQ (β = .143), IM toward Accomplishment (β = .144), CGPA (β = .115), IM to Experience Stimulation (β = −.141), EM Introjected (β = .101), ASL (β = − .074) and global PSQI (β = − .060), and effect size was medium (f2 = 0.183). For Neuroticism, 6.1% of the variance was explained by global PSQI (β = .195), ASL (β = .073), AMS-C (β = − .091), CGPA (β = .070), IM toward Accomplishment (β = .121) and IM to Know (β = − .105). The effect size of the analysis was small (f2 = 0.065). And for Openness to Experience, 9.1% of the variance was explained by AMS-C (β = .168) and IM to Know (β = .162), and effect size was small (f2 = 0.100). 4. Discussion and conclusion In the current study, CGPA was found to relate with Circadian Preference (Morningness–Eveningness), Academic Motivation, Personality traits (Agreeableness, Conscientiousness) and Sleep Patterns (MSFsc and Social Jetlag). Similar results were reported in previous researches (Beşoluk et al., 2011; Borisenkov et al., 2010; Gomes et al., 2011; Komarraju et al., 2009; Vollmer, Pötsch, & Randler, 2013; Wolfson & Carskadon, 2003). The regression analysis clarified the nature of the relationship between CGPA and other variables (chronotype/Circadian Preference, Sleep Quality and Sleep Patterns, Big Five Personality traits and Academic Motivation). MSFsc, AMS-C, Social Jetlag and Conscientiousness were the main predictors of Academic Achievement. Meanwhile, IM toward Accomplishment, IM to Experience Stimulation and Neuroticism also contributed to the variance explained. Students who are more morning-oriented, have a desire to accomplish, are more conscientious and neurotic and are likely to have higher CGPA scores. Since MSFsc is the best marker for sleepbased assessments of chronotype (Juda et al., 2013), a negative relation of MSFsc and Social Jetlag with CGPA indicates that students with morning chronotype and with less sleep debt have higher CGPA scores. O'Connor and Paunonen (2007) have indicated that since conscientious students are more motivated, self-disciplined and diligent, they may perform better academically than less conscientious students. Meanwhile, conscientious students are more motivated to perform well academically, so the relationship between Conscientiousness and Academic Achievement should be interpreted with consideration for motivation (Chamorro-Premuzic & Furnham, 2005; O'Connor & Paunonen, 2007). In the current study the highest correlation between Personality traits and Academic Achievement was observed between Conscientiousness and Academic Achievement. This supports the notion that conscientious students are more motivated and more morning-oriented than less conscientious students and therefore have higher CGPA scores. However, the weak relationship between Neuroticism and CGPA is interesting and a similar result was reported in the literature (Komarraju & Karau, 2005; Komarraju et al., 2009; Spinath, Freudenthaler, & Neubauer, 2010). This relationship may indicate that students with high academic ambition may also experience some degree of anxiety about being successful (Komarraju et al., 2009). In the regression analysis regarding CGPA, chronotype (MSFsc) appeared as a predictor like many studies in the literature

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(Borisenkov et al., 2010; Randler & Frech, 2006). Unlike many studies which indicate that Sleep Quality is related to Academic Achievement (Curcio et al., 2006; Gilbert & Weaver, 2010; Wolfson & Carskadon, 2003) in this study Sleep Quality did not correlate with Academic Achievement. However, the Sleep Quality of the sample in general was poor (66.23%) and the sample was gender biased, which may have affected the results, since the achievement of female students is generally high. Thus we have investigated whether both Sleep Quality and chronotype have an effect on CGPA, both in the female and male samples, and have found a significant effect of chronotype but no effect of Sleep Quality on CGPA in both samples. The CGPA scores of earlier chronotypes were higher than those of later chronotypes. A significant portion of courses in the university are taught before noon, and therefore earlier chronotypes are at an advantage, since they are more active both cognitively and psychologically earlier in the day, which may help them to attain higher grades. MEQ was correlated to global PSQI, AMS-C, Agreeableness, Conscientiousness, CGPA, MSFsc and ASL. Similar results were reported in literature regarding MEQ (DeYoung et al., 2007; Randler, 2008; Roenneberg et al., 2004; Roeser et al., 2013; Tonetti et al., 2009; Vardar et al., 2008). MSFsc, global PSQI, Conscientiousness, EM External Regulation and IM to Experience Stimulation, Social Jetlag, Extraversion, IM toward Accomplishment and IM to Know emerged as significant predictors of MEQ. MSFsc is a good predictor of MEQ as aforementioned. Moreover, students who sleep well, are more conscientious, less externally regulated and engage in activity for fun and excitement, and are more likely to have morning circadian typology. Our Sleep Quality analysis in the female sample supports this finding, where the Sleep Quality of MT students was better than both NT and ET students, meanwhile the Sleep Quality of ET students was the worst. Similar results were reported by Lima et al. (2010). Besides, MT students were more conscientious, and of the Big Five Personality traits, Conscientiousness best discriminates the three circadian typologies. A similar result was reported by Tonetti et al. (2009). Further, our findings show that MT students engage in activity not because of external demands or possible rewards but for the experience of sensory stimulation. This study found that Academic Motivation of female MT students was higher than both NT and ET students. Female students are generally more achievement-oriented and display some anxiety with regard to their academic success, and as a result may have poor Sleep Quality. Meanwhile they are more morning-oriented, which confers an advantage in the teaching and learning process, since most teaching is scheduled during the morning. As such, they may have higher CGPA scores. Regression analysis showed that Conscientiousness, CGPA, Openness to Experience, Neuroticism and Social Jetlag were the significant predictors of AMS-C. Regarding the three domains of Motivation (Intrinsic, Extrinsic and Amotivation); Personality traits, CGPA and MSFsc emerged as predictors. Our results indicated that Personality traits, Academic Achievement and circadian typology are related with a wide variety of Academic Motivations. Openness and Conscientiousness were positively related with Motivation, while Neuroticism was negatively related. Students who are intellectually curious, disciplined, organized and less neurotic are likely to have higher Academic Motivation. Our findings are to some extent similar to Komarraju and Karau (2005) and Komarraju et al. (2009). Personality traits in general correlate with Academic Motivation or with its sub-domains. Extraversion, Agreeableness, Conscientiousness and Openness to Experience were found to correlate positively while Neuroticism correlated negatively with the Academic Motivation. Meanwhile regression analysis presented that in all Personality traits; Academic Motivation/sub-domains of Academic Motivation and in some Personality traits; ASL, circadian typology and Academic

M: Mean; SD: Standard Deviation; MEQ: Morningness–Eveningness Questionnaire; AMS-C: Self-determination index; MSFsc: Corrected mid-sleep time on free days; ASL: Average Sleep Length; Global PSQI: Global Pittsburgh Sleep Quality Index; CGPA: Cumulative Grade Point Average; M-type: Morning type; N-type: Neither type; E-type: Evening type.

10.3 10.1 9.6 9.0 9.8 ± ± ± ± ± 49.7 49.2 50.8 51.8 49.8 ± 2.7 ± 2.8 ± 2.9 ± 2.7 ± 3.0 7.3 7.3 6.8 6.6 6.5 01:00 01:10 01:01 01:04 01:12 ± ± ± ± ± 01:18 00:59 00:54 00:49 00:52 01:15 01:09 01:16 01:17 01:23 ± ± ± ± ± 07:58 07:57 08:09 08:12 08:02 ± 01:37 ± 01:28 ± 01:29 ± 01:39 ± 01:54 06:16 05:54 06:00 06:02 05:57 7.7 7.3 7.3 6.8 8.2 ± ± ± ± ± 42.3 42.1 42.8 43.4 42.0 7.4 6.9 7.3 7.8 7.2 ± ± ± ± ± 24.0 24.1 24.0 23.8 22.8 7.2 7.1 6.2 7.1 8.2 ± ± ± ± ± 38.0 37.6 38.3 37.6 36.8 8.2 8.7 8.4 7.9 9.7 ± ± ± ± ± 49.4 49.4 50.4 50.7 49.4 9.9 9.2 8.9 9.4 10.0 ± ± ± ± ± 45.7 45.5 47.3 46.5 44.8 3.6 3.7 4.3 4.5 4.7 ± ± ± ± ± 219 267 294 255 176

± ± ± ± ±

9.0 8.3 8.9 8.4 9.6 50.7 50.6 51.0 50.9 51.3 Age 19− 20 21 22 23+

6.8 6.2 5.8 4.9 4.4

50.5 ± 9.8 49.8 ± 10.0 4.0 ± 0.9 8.4 ± 2.3 00:48 ± 00:59 01:05 ± 01:08 08:19 ± 01:04 07:53 ± 01:21 05:48 ± 01:29 06:13 ± 01:40 43.2 ± 7.3 42.4 ± 7.6 22.2 ± 6.9 24.5 ± 7.47 38.7 ± 6.7 37.2 ± 7.3 50.4 ± 8. 6 49.5 ± 8.6 47.5 ± 9.1 45.5 ± 9.7 52.9 ± 8.4 49.8 ± 8.8 Sleep Quality Good 394 Poor 773

6.0 ± 4.1 5.7 ± 4.3

52.1 ± 9.2 48.1 ± 10.1 6.6 ± 2.8 7.2 ± 2.8 00:42 ± 01:02 01:17 ± 01:06 07:49 ± 01:12 08:14 ± 01:20 04:48 ± 00:45 07:18 ± 01:16 42.5 ± 7.5 42.6 ± 7.5 23.8 ± 7.4 23.5 ± 7.1 38.5 ± 6.8 36.9 ± 7.2 50.1 ± 8.6 49.4 ± 8.6 46.1 ± 9.7 46.2 ± 9.4 54.0 ± 7.9 47.7 ± 8.5 Chronotype (MSFsc) Earlier 631 Later 620

5.9 ± 4.3 5.6 ± 4.1

51.8 ± 9.7 49.9 ± 9.7 49.4 ± 10.1 6.3 ± 2.6 6.9 ± 2.8 8.0 ± 3.2 00:48 ± 00:56 01:01 ± 01:04 01:01 ± 01:25 07:51 ± 01:09 08:06 ± 01:11 08:22 ± 01:38 05:10 ± 01:29 06:01 ± 01:28 07:14 ± 01:42 43.5 ± 7.6 42.3 ± 7.2 42.2 ± 7.9 23.1 ± 7.7 24.0 ± 7.1 24.3 ± 7.7 39.5 ± 6.4 37.5 ± 7.0 35.7 ± 7.9 51.2 ± 8.5 49.9 ± 8.4 48.3 ± 8.9 47.0 ± 10.1 45.6 ± 9.2 46.4 ± 9.4 62.6 ± 3.6 50.4 ± 4.5 36.4 ± 3.9 Chronotype (MEQ) M-type 263 N-type 802 E-type 186

6.6 ± 4.4 5.5 ± 4.1 5.0 ± 4.4

52.5 ± 9.1 45.7 ± 9.8 7.1 ± 2.8 6.7 ± 2.9 00:54 ± 01:02 01:08 ± 01:12 08:02 ± 01:11 08:02 ± 01:26 05:47 ± 01:23 06:33 ± 01:52 42.9 ± 7.2 41.9 ± 8.1 24.4 ± 7.4 22.4 ± 6.9 38.0 ± 6.9 37.0 ± 7.5 50.5 ± 7.9 48.5 ± 9.6 46.5 ± 9.2 45.3 ± 10.0 51.2 ± 8.8 50.2 ± 8.9 813 432

6.6 ± 3.7 4.1 ± 4.6

50.0 ± 9.9 08:02 ± 01:17 06:04 ± 01:38 42.5 ± 7.6 23.7 ± 7.2 37.6 ± 7.2 49.7 ± 8.6 46.0 ± 9.6 5.7 ± 4.2 50.9 ± 8.8 1251

Neuroticism Conscientiousness Agreeableness

01:00 ± 01:06

6.9 ± 2.8

Global PSQI Social Jetlag ASL Sleep Patterns

MSFsc Extroversion

Openness to Experience Personality

Motivation (AMS-C) MEQ

Gender Female Male

We are grateful to the students of Sakarya University Faculty of Education who participated in this study. This study was supported by the Research Fund of Sakarya University (Project Number: 201206-01-001).

Total

Acknowledgments

N

Achievement emerged as significant predictors. Several studies presented that Academic Motivation, circadian typology and Academic Achievement are related to Personality traits (Clark & Schroth, 2010; Komarraju et al., 2009; Roeser et al., 2013). In the current study, IM to Know was a positive predictor of Extraversion and Openness to Experience while a negative predictor of Neuroticism. This result shows that students who are social, active, ambitious, literate, open-minded and emotionally stable can be expected to have an intrinsic motivation to learn new things for pleasure. A similar result was reported by Clark and Schroth (2010), where they indicated that Extraverted and Open students tend to be Intrinsically Motivated to Know, and Neurotic students attend university out of a sense of obligation. Meanwhile, in the current study IM toward Accomplishment was a positive predictor of Conscientiousness and Neuroticism, but a negative predictor of Agreeableness. Those students who are self-disciplined, responsible and less flexible have an intrinsic motivation to surpass themselves, but they experience stress and anxiety in that process. Further, IM to Experience Stimulation was a negative predictor of Conscientiousness, which implies that self-disciplined and responsible students have an Intrinsic Motivation to experience pleasant sensations. Besides, students who are emotionally unstable sleep more but their Sleep Quality is poor since ASL and global PSQI were positive predictors of Neuroticism. Emotionally unstable students are also likely to have more sleep problems (Gau, 2000), and therefore they spend more time in bed. However, ASL was a negative predictor of Conscientiousness and Agreeableness. Conscientious students spend more time studying, and Agreeable students are more optimistic, calm, emotionally stable, and free from persistent negative feelings (Henle & Gross, 2013) so they sleep well but for less time. In conclusion, this study extends our understanding of the effect of Personality traits, Academic Motivation, circadian typology, Sleep Quality and Sleep Patterns in explaining Academic Achievement and the relationship among these variables. In the current research the variables investigated explained just 15.1% of the variation in Academic Achievement. Although this may be seen as a small variation, the current findings show that Personality, sleep variables, chronotype and Motivation affect Academic Achievement. All the variables investigated in this research were interrelated to some extent, and the effects of some of them vary with respect to gender. However, there are other important features that differ individually (e.g. intelligence, learning style, learning autonomy, learning approach, thinking style, creativity, problem solving skills etc.) and also affect Academic Achievement and educational outcomes. Therefore, these individual differences and their interactions could be investigated broadly, deeply and longitudinally by applying both qualitative and quantitative research methods to clarify the construction of interactions. There are some limitations in the study and results regarding these limitations should be interpreted with caution. The correlation coefficients obtained are generally low. Meanwhile, most of the participants in the study reported poor Sleep Quality. This may in turn affect related results. Moreover, the sample is gender biased although it represents the population, and female students are more morning-oriented in the sample age range, so the proportion of MT students is higher than ET students.

CGPA (t scores)

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Appendix 1. Descriptive statistics (M ± SD)

190

.217a .331a −.253a ns −.184a ns −.061b ns

Openness to Experience

ns .062b ns ns ns

Neuroticism

ns .514a ns −.125a −.085 ns

Conscientiousness

.505a −.148a .545a .200a −.060b −.103a ns

Agreeableness

.398a .471a ns .725a .101a ns −.072a ns .198a .227a .283a −.091a .277a .064b ns −.065b ns −.791a −.113a −.202a −.206a .088a −.151a .221a .058b ns ns −.186a .477a .125a .090a .228a ns .191a −.166a .113a .058b ns .687a −.158a .686a .192a .096a .239a ns .272a .124a ns ns ns ns ns .067b −.055b −.059b ns −.095a .183a ns .166a .144a −.178a .129a ns −.081a −.082a .114a ns .128a .190a −.071b .065b ns −.437a −.134a −.088a CGPA (t scores) Sleep Patterns

−.211a Intrinsic Extrinsic Amotivation AMS-C Extroversion Agreeableness Conscientiousness Neuroticism Openness to Experience .106a MSFsc ASL Social Jetlag MEQ Global PSQI Academic motivation

Personality

Personality

Extroversion AMS-C Amotivation Extrinsic

Academic Motivation

Intrinsic Global PSQI MEQ

Appendix 2. Correlations

ns: Not statistically significant. MEQ: Morningness–Eveningness Questionnaire; AMS-C: Self-determination index; Global PSQI: Global Pittsburgh Sleep Quality Index; CGPA: Cumulative Grade Point Average; MSFsc: Corrected mid-sleep time on free days; ASL: Average Sleep Length. a Correlation is significant at the 0.01 level. b Correlation is significant at the 0.05 level.

−.145a

ASL MSFsc CGPA (t scores)

Sleep Patterns

Social Jetlag

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