The relation between
chronotype, sleep duration and behavioral
problems in school-aged children.
Master Thesis
University of Leiden, Faculty of Social and Behavioral Sciences Department Clinical Child and Adolescent Studies
Student: L.S.E. de Vreugd
Student number: S0306622
Date: 2012 -2013
Page 2 Abstract
Background. Chronotype influences both sleep characteristics and behavior. Evening oriented children are more at risk to develop behavioral problems compared to morning oriented children. Insufficient sleep is common during childhood and can lead to behavioral problems. However, the association of sleep duration, chronotype and behavioral problems remains unclear, especially in children. Therefore, the current study examined the degree to which sleep duration acts as a mediator of the influence of chronotype on behavioral problems in Dutch non-clinical 9-11 year old children.
Method. The sample consisted 483 children, 219 boys and 264 girls, with a mean age of 10.49 year old. Sleep duration was assessed with sleep diaries. Chronotype was measured using Children´s Chronotype Questionnaire (CCTQ) and behavioral problems were assessed with Strengths and Difficulties Questionnaire (SDQ).
Results. Regression analyses showed chronotype was a significant predictor of sleep duration (= -.10, p = .035), externalizing ( = .10, p = .030), but not internalizing behavioral problems (= .04, p = .410). Sleep duration was not significantly related to internalizing and externalizing behavioral problems. Furthermore, sleep duration did not act as a mediator between chronotype and internalizing (= .01, p = .900) or externalizing behavioral problems (= -.01, p = .869).
Page 3
The relation between chronotype, sleep duration and behavioral
problems in school-aged children
Individual differences in sleep-wake patterns determine whether someone is more active and alert early or late during the day. This continuum is referred to as chronotype or morningness-eveningness (Kerkhof, 1985). Behavioral problems and sleep have both been reported to be associated with chronotype (Astill, Van der Heijden, Van IJzendoorn, & Van Someren, 2012). It has been found that insufficient sleep can impact several aspects of a person‟s functioning, including aspects of cognitive and behavioral functioning (Astil et al., 2012; Pilcher, & Huffcutt, 1996). Sleep problems are very common in childhood (Hoedlmoser, Kloesch, Wiater, & Schabus, 2010) and are associated with behavioral problems which may result in inadequate and/or insufficient sleep. A strong relation between insufficient sleep and behavioral problems has been found. However, while many studies focused on sleep problems (Paavonen et al., 2002), only few studies focused on sleep duration and the consequences of short sleep (Hoedlmoser et al., 2010). Furthermore, it remains unclear how sleep duration influences of chronotype on behavioral problems. Therefore, more sleep research focusing on children is needed to give better insight and understanding of the association between sleep, chronotype and behavioral problems (Astill et al., 2012). The present study presents research as to whether sleep duration mediates the relation between chronotype and behavioral problems in 9-11 year old children. In addition, underlying associations between chronotype, sleep duration, and behavioral problems are explored. Previous research reported poor school results are associated with both short sleep (Gregory et al., 2005; Lange & Randler, 2011) and evening orientation (Preckel, Lipnevich, Schneider, & Roberts, 2011). It is important to better understand how sleep, chronotype and behavioral problems interact, since these insights will help find ways to help students improve their school performances. Persistent insufficient sleep may increase risk to develop psychiatric disorders (Lange & Randler, 2011). When more is known about the effects of insufficient sleep and how this influences chronotype and behavior, better ways to treat behavioral problems can be developed. Early intervention might prevent problems later in life.
Chronotype and problem behavior
Page 4 Natale & Cicogna, 2002). Chronotype orientation is determined by psychological, biological factors and environmental factors (Barclay, Eley, Parsons, Willis, & Gregory, 2013; Carskadon, Vieira, & Acebo, 1993). Children often have a tendency towards morningness, which shifts towards eveningness when children reach the age of approximate 13 years. This applies to both girls and boys (Kim, Dueker, Hasher, & Goldstein, 2002). At the end of puberty, chronotype orientation shifts back towards morningness (Roenneberg et al., 2004). Both adults and children with an evening chronotype, tend to sleep shorter compared to people with a morning chronotype (Giannotti, Cortesi, Sebastiani, & Ottaviano, 2002; Violani, Devoto, Lucidi, Pedacchio, & Rifezzo, 1997). Research revealed evening chronotype is a possible pre-condition to develop psychiatric disorders in later life (Lange & Randler, 2011). Therefore, it is important to get a better understanding of the relation between chronotype and behavior. This relation has been studied in adolescents, and it has been found that adolescents with an evening chronotype are more at risk to develop behavioral problems (Gau et al., 2007; Goldstein, Hahn, Hasher, Wiprzycka, & Zelazo, 2007; Lange & Randler, 2011). However, no consensus in the literature has been found as to whether eveningness is associated with only with both internalizing and externalizing behavioral problems (Gau et al., 2007) or only with externalizing behavioral problems (Goldstein et al., 2007; Lange & Randler, 2011). Lange and Randler (2011) studied the relation between sleep and behavior in 11 to 18 year old adolescents. They noted that girls are more at risk to develop behavioral problems than boys, since girls often are more frequently evening oriented. To what extent these results apply to other age groups remains unclear. Thus more research is needed to investigate if those results apply to children as well (Gau et al., 2007; Goldstein et al., 2007).
Sleep and problem behavior
Page 5 slightly more hours than boys on weekdays as well as weekends (Gulliford et al., 1990; Liu et al., 2000; Spruyt et al., 2005). Hoedlmoser et al. (2010) reported girls only sleep longer than boys during weekends. It has been suggested that insufficient sleep is the cause of inappropriate or problem behavior in children (Dahl, 1996; Fallone, Acebo, Arnedt, Seifer, & Carskadon, 2001; Hoedlmoser et al., 2010; Paavonen, Porkka-Heiskanen, & Lahikainen, 2009). Fallone et al. (2001) found more inattentive behavior in 8 to 15 year olds who were only allowed to sleep for four hours (Fallone et al., 2001). Several association studies on sleep and behavior showed short sleep is associated with both internalizing and externalizing behavioral problems (Aronen, Paavonen, Fjallberg, Soininen, &Torronen, 2000; Astill et al., 2012; Paavonen et al., 2009). Aronen et al. (2000) found that both internalizing and externalizing behavior problems are associated with short sleep duration in 7-12 year old children. Aronen et al. (2000) divided the participants in three different groups, namely children who slept on average (A) 9.6 (range 9.3- 10.2), (B) 8.9 (range 8.6- 9.2) or (C) 8 (range 7.3- 8.4) hours per night. Teachers reported less behavioral problems for group A than for group B. Group C had more internalizing and especially more externalizing behavioral problems than both other groups. However, those behavioral problems were only reported at school and not at home. This could be due to different demands of the situation. At school children have to concentrate and listen. While at home children have more freedom to choose what they want to do, thus signs of effects of insufficient sleep may not always be noticed by parents (Paavonen et al., 2009). Paavonen et al. (2009) found short sleep duration increased the risk for symptoms of attention-deficit/hyperactivity disorder in 7-8 year old children. Since there is a disagreement in literature whether short sleep duration is also associated with behavioral problems at home, more research is needed.
Sleep duration as mediator between chronotype and behavioral problems
Previous research revealed associations between the variables chronotype, sleep duration, and behavioral problems (Astill et al., 2012; Giannotti et al., 2002; Goldstein et al., 2007; Violani et al. 1997). This suggests it is possible that sleep duration acts as a mediator on the influence of chronotype on behavioral problems. Until now this has not been explored. Therefore, the current study aims to explore this association in a group of non-clinical school-aged children. The main question of this study is:“Does sleep duration mediate the relation between
Page 6 chronotype, sleep duration and behavioral problems are explored. The expectation is that evening chronotype is associated with increased behavioral problems (Goldstein et al., 2007; Lange & Randler, 2011). In addition, it is hypothesized that short sleep is associated with evening chronotype (Giannotti et al., 2002; Violani et al., 1997), increased internalizing and externalizing behavioral problems (Aronen et al., 2000; Astill et al., 2012; Paavonen et al., 2009). Furthermore, it is expected that sleep duration mediates the relation between chronotype and behavioral problems.
Method
Participants
The current study was part of a Dutch study on the relation between sleep characteristics and learning ability of 9-11 year old children and was conducted in collaboration with the Dutch Sleep Registry. The sample was defined by non-clinical school-aged children (9-11 years old). Participants were mainly recruited from mainstream elementary schools in the Netherlands, but also from child daycares and social networks of the researchers. Of the 154 schools and child daycare centers approached, only 94 schools received the information letter.
Consent for participation was received from 54% of the schools. After schools and child daycare facilities gave their consent, a total of 4409 parents were approached of whom 4323 parents received information about the study. Written informed consent was obtained from 653 parents (response rate 15%) of whom 47 withdrew before the start of the study. Not filling out instruments used to measure chronotype, behavior and sleep (n = 121), and not providing background information like gender and age (n = 2) were used as exclusion criteria. The sample consisted 483 children, of whom 219 boys and 264 girls. The mean age was 10.49 years (SD = 0.85, range 8.98-12.47). The majority (97.5%) of the participants had Dutch nationality. Most of the children (88.3%) were living with both parents. For 88.9 percent of the children the questionnaires were filled out by their mother. The majority of the respondents received a college level education (47.1%) or at least secondary education (35%).
Procedure
Page 7 were provided with several questionnaires. Parents completed seven questionnaires (45 minutes). The questionnaire issued to parents covered topics concerning background information such as gender, age, and nationality of the child, gender of the respondent, relationship of respondent to child and family situation. Other questionnaires were used to obtain information about behavioral problems (SDQ; Goodman, 2001), chronotype (CCTQ; Werner, LeBourgeois, Geiger & Jenni, 2009), sleep disorders (SDSC; Bruni et al., 1996), temperamental characteristics (BIQ; Bishop, Spence, & McDonald, 2003) of the child, and sleep characteristics and sleep history of the parents (combination of Pittsburgh Sleep Quality Index; Buysse, Reynolds III, Monk, Berman, & Kupfer, 1989; and Insomnia Severity Index Scale; Morin, 1993). Children filled out two questionnaires (25 minutes) to assess temperament (EATQ-R; Ellis & Rothbart, 2001) and to obtain information about pubertal status (PDS; Petersen, Crockett, Richards & Boxer, 1988). Besides that, children had to perform an 8-minute memory task four times on the computer at home. At the last day of the research week the child performed three computer tasks with the examiner at either school / child daycare or at the child´s home. The total approximate duration of this examination was 30 minutes. The Psychomotor Vigilance Task (PVT) and PVT Go/No-Go was applied to measure the ability of sustained attention and inhibition. Furthermore, the Digit Span Task forwards and backwards were used to measure working memory's number storage capacity. The computer tasks were always performed in the order as listed. The test moments were only planned on weekdays from Tuesday till Friday after 10.00 a.m. and could not take place in or just after school holidays.
Measurements
Chronotype
Page 8 Those ten questions were used to calculate a score for ´morningness/eveningness´. The morningness/eveningness scores ranged from 10 (extreme morningness) to 48 (extreme eveningness). The higher the score, the more a child tended towards eveningness. Werner et al. (2009) found a good internal consistency (α = .81) for the 10 items of the MESC that estimate morningness/eveningness. In addition, the CCTQ has a good retest stability after 2-4 weeks(r: .74 - .92). Thus, the CCTQ is found to be reliable and valid (Werner et al., 2009).
Sleep duration
Sleep duration was calculated using sleep diaries. Parents kept a sleep diary for their child during eight days. In the evening they kept track of bed time and time falling asleep. Additionally, parents were asked to report awakening time in the morning. For each day sleep duration was calculated from sleep onset (time lights out plus sleep latency) to awakening. For the whole week the mean sleep duration was calculated. Only children for whom sleep times were provided for at least four days were included in data analyses. In general, subjective measurements like sleep diaries have been found to be valid and reliable to assess sleep duration compared to more objective methods (Lauderdale, Knutson, Yan, Liu, & Rathouz, 2008; Lockley, Skene, & Arendt, 1999). However, there is a tendency to overestimate sleep duration with self-report measurements (Lauderdale et al., 2008; Lockley, Skene & Arendt, 1999).
Behavioral Problems
Page 9 probably has an internalizing or externalizing disorder (Goodman, 2001). Goodman (2001) investigated the psychometric properties of the SDQ. He found very little overlap between items on the scales measuring internalizing and externalizing behavioral problems. Found correlation between the scales internalizing and externalizing behavior was moderate (r = .30). Thus the SDQ had a good ability to discriminate between internalizing and externalizing behavioral problems. Furthermore, a reasonable retest stability was found after 4 to 6 months (α = .62). All analyses indicated the reliability and validity of the SDQ were acceptable to good (Goodman, 2001).
Statistical analysis
Page 10 Results
Subject Characteristics
The majority of the participants had a tendency towards morningness (M = 27.58, SD = 28.58, range 14-45).When looking at chronotype it was observed that girls are slightly more often evening orientated compared to boys. However, no difference in sleep duration between girls and boys was found. The average daily sleep duration of the participants was 599.54 minutes (SD = 33.84, range 487-697). Gender differences between behavioral problems were analyzed separately for both internalizing and externalizing behavioral problems. The mean score for internalizing behavioral problems was 2.98 (SD = 2.67, range 0-12). There was no difference in amount of internalizing behavioral problems between boys and girls (Table 1). Furthermore, the mean score for externalizing behavioral problems was 3.99 (SD = 3.23, range 0-14). In contrast to internalizing behavioral problems, there was a significant difference in the amount of externalizing behavioral problems between boys (M = 4.40, SD = 3.35) and girls (M = 3.63, SD = 3.09), t (475) = 2.61, p .010. In Table 1 the mean scores, standard deviations and t-tests can be found for boys and girls on age, sleep duration, chronotype and behavioral problems. Beside gender differences, differences in age were also explored. Girls were slightly older than boys, t (475) = -2.11, p = .035. A significant small positive correlation was found between age and chronotype, r (450) = .16, p = .050. Indicating, older children tend more towards eveningness. In addition, increased age was associated with a decrease in average daily sleep duration, r (450) = -.33, p = .010. Behavioral problems were not significantly different for younger and older children in this sample.
Table 1.
Independent t-tests: gender differences on chronotype, sleep duration and behavioral problems (N=477).
Boys (N = 218) Girls (N = 259)
M SD M SD t DF p
Age (years) 10.41 0.86 10.57 0.84 -2.11 475 .035*
Chronotype 26.58 4.87 28.42 5.17 -.3.97 475 .010**
Sleep duration (minutes) 598.23 33.01 600.63 34.54 -0.75 450 .455
Internalizing behavioral problems 2.95 2.81 3.00 2.55 -0.22 475 .825
Externalizing behavioral problems 4.40 3.35 3.63 3.09 2.61 475 .010**
Page 11 Association between chronotype, sleep duration, and behavioral problems
A significant small negative correlation was found between chronotype and average daily sleep duration, r (450) = -.09, p = .035. Indicating that a high score on chronotype is associated with shorter sleep duration. Also, no significant correlation was found between chronotype and internalizing behavioral problems, r (475) = .10 p = .552. In contrast, a significant small positive correlation was found between chronotype and externalizing behavioral problems, r (475) = .27, p = .034. Indicating a high score on chronotype is often found in combination with a high score on externalizing behavioral problems. Furthermore, no significant relations were found between average daily sleep duration and either internalizing or externalizing behavioral problems (Table 2).
Table 2.
Pearson correlation between age, chronotype, sleep duration, and internalizing and externalizing behavioral problems.
N M SD 1 2 3 4
1. Age 477 10.50 0.09
2. Chronotype 477 27.58 0.23 .16**
3. Sleep duration 452 599.54 1.59 -.33** -.09*
4. Internalizing behavioral problems 477 1.48 0.04 -.06 .04 <.01
5. Externalizing behavioral problems 477 1.74 0.05 -.05 .10* -.02 .27**
* p <.05, ** p <.01.
Mediation effect of sleep duration
Four steps by Baron and Kenny (1986) were used to investigate the possibility of sleep duration acting as a mediator between chronotype and both internalizing and externalizing behavioral problems.
First, the possible mediation effect of sleep duration on chronotype and internalizing behavioral problems was investigated. A regression analysis showed chronotype did not predict internalizing behavioral problems (YX = .04, t (475) = .83 p = .410). Conversely,
chronotype did predict sleep duration (ZX = -.10, t (450) = -2.12, p = .035). Furthermore,
sleep duration did not predict internalizing behavioral problems when chronotype was controlled for, YZ.X = .05, t (462) = 1.15, p = .249. In addition, chronotype failed to predict
internalizing behavioral problems when sleep duration was controlled for, YX.Z = .01, t (462)
Page 12 effect/mediation would be impossible thus a Sobel test was not calculated. There was no mediation effect found.
Secondly, it was investigated whether there was a mediation effect of sleep duration on chronotype and externalizing behavioral problems. Chronotype was a predictor of externalizing behavioral problems (YX = .10, t (475) = 2.18 p = .030). Additionally,
chronotype did predict sleep duration (ZX = -.10, t (450) = -2.12, p = .035). Furthermore,
sleep duration did predict externalizing behavioral problems when was controlled for, YZ.X =
.11, t (449) = 2.23, p = .026. However, chronotype failed to predict externalizing behavioral problems when sleep duration was controlled for, YX.Z = -.01, t (449) = -.17, p = .869.
Complete mediation could be possible, since several regression analyses were significant. However, the Sobel test showed no significant results, Z = -1.53, p > .050. Again, no mediation effect was found.
Discussion
The aim of this study is to determine the relation between chronotype, sleep duration, and behavioral problems in non-clinical Dutch 9-11 year old children. The main question is “Does sleep duration act as a mediator between chronotype and either internalizing or externalizing behavioral problems in school-aged children”. It is hypothesized that sleep duration acts as a
mediator of chronotype influence on both internalizing and externalizing behavioral problems. Underlying associations are investigated before possible meditation effects were studied.
Page 13 participants could be classified as evening or morning oriented while they are actually intermediate. Thus it can´t be verified if the chance of evening orientation is greater for girls.
Results revealed chronotype is not associated with internalizing behavioral problems. This confirms results of some previous studies in children and adolescents (Goldstein et al., 2007; Lange & Randler, 2011). In contrast to research on children, it is reported that evening orientation is a risk factor to develop depressive symptoms in adolescents (Gau et al., 2007) and adults (Chelminski, Ferraro, Petros, & Plaud, 1999; Drennan, Klauber, Kripke, & Goyette, 1991). Although the findings on adults apply to clinical depressed patients, while the current study focused on healthy children. Again, differences in findings might be affected by the use of a continuous scale for chronotype instead of a cutoff score to divide participants in groups for chronotype.
In contrast, chronotype is associated with externalizing behavioral problems. Children who are more evening oriented exhibit higher levels of externalizing behavioral problems as reported by parents/caretakers. This is in accordance to previous results (Gau, et al., 2007; Goldstein et al., 2007; Lange & Randler, 2011). Externalizing behavioral problems may be the consequence of lack of sleep (Aronen et al., 2000; Dahl, 1996; Fallone et al., 2001; Hoedlmoser et al., 2010; Paavonen et al., 2009). When going to school evening oriented children have to wake-up earlier than their optimal wake-up time. This may lead to insufficient sleep, since evening oriented children prefer late bed and rising times. Morning oriented children don´t have this problem, because school times are a better match with their preferences for early bed and rising times (O‟Malley & O‟Malley, 2008; Preckel et al., 2011). This is confirmed by the current study, as the results reveal evening oriented children sleep for fewer hours than morning oriented children.
Another aim of the study is to investigate the relation between sleep duration and behavioral problems. No association between sleep duration and internalizing behavioral problems was found. In contradiction, previous studies show insufficient sleep is associated with internalizing behavioral problems (Aronen et al., 2000; Paavonen et al., 2009). Differences in mean total sleep duration may account for discrepancy in results between the current study and previous research. Whereas, children in the current study sleep longer, on average, than children from the previous studies. Though this difference in sleep time might
be caused by the use of sleep diaries instead of objective measurements for sleep duration as
used by other studies. In contrast, short sleep duration is associated to externalizing behavioral
Page 14 by a decrease in sustained attention and inhibition when a child sleeps for fewer hours
compared to peers (Curcio, Ferrara & Gennaro, 2006).
Even though sleep duration is associated with chronotype and externalizing behavioral problems, sleep duration does not act as a mediator between chronotype and either internalizing or externalizing behavioral problems. Previous studies have not researched this possibility of mediation. Despite the indication that sleep duration does not act as a mediator on chronotype and behavioral problems, mediation might still be possible in older age groups.
Inasmuch, chronotype orientation shifts towards eveningness at age 13 (Kim et al., 2002) and
children experience a decrease in sleep time as age increases (Iglowstein et al., 2003; Ohayon
et al., 2004). These changes in chronotype orientation and sleep duration might affect the found relation.
This study is unique insofar as it is one of the first times that research has been undertaken to explore the possible mediation effect of sleep duration on the relation between chronotype and sleep duration. Other strengths of the study are a relatively large sample and the use of reliable and valid measurements to assess chronotype and behavioral problems. Yet the results should be interpreted with respect to limitations of the study. The study utilizes subjective measures provided to parents to assess observable aspects of sleep. However, some
aspects of sleep might not be observed by parents, i.e. if the child wakes up in the middle of the night (unless the child wakes up the parents). Yet this method was chosen, because it is cheaper and can be used by parents instead of a researcher. Future research can overcome this limitation by using actigraphy to measure sleep characteristics in combination with self-report measurements. In this manner associations between sleep and other variables can be compared for both subjective and objective sleep measurements. Another limitation of this study is its correlational nature. Thus, nothing can be said about casual relations between
chronotype, sleep duration and behavioral problems. Longitudinal experimental research on
Page 15 according previous studies, may lead to psychopathology later in life (Lange & Randler, 2011). In addition, children with an evening orientation are more likely to experience insufficient sleep. More flexible school times adjusted to optimal bed and rise times, might be a solution. Research is needed to investigate this. Screening for chronotype can help early to identify children who are more evening orientated. Evening orientated children are more at risk to develop clinical behavioral problems, since they exhibit more externalizing behavioral problems. Early intervention to shift chronotype orientation to morningness may prevent problems later in life. However, more research is needed to provide understanding how the relation between chronotype, sleep duration and behavioral problems develop in different age groups.
References
Aronen, E. T., Paavonen, E. J., Fjallberg, M., Soininen, M., & Torronen, J. (2000). Sleep and psychiatric symptoms in school-age children. Journal of the American academy of child and adolescent psychiatry, 39, 502-508.
Astill, R. G., Van der Heijden, K. B., Van IJzendoorn, M. H., & Van Someren, E. J. W. (2012). Sleep, cognition, and behavioral problems in school-age children: a century of research meta-analyzed. Psychological bulletin, 138, 9-1138. doi:10.1037/a0028204. Barclay, N. L., Eley, T. C., Parsons, M. J., Willis, T. A., & Gregory, A. M. (2013).
Monozygotic twin differences in non-shared environmental factors associated with chronotype. Journal of biological rhythms, 28, 51-61. doi:10.1177/0748730412468698.
Baron, R. M., & Kennedy, D. A. (1986). The moderator-mediator variable distinction in social psychological research: conceptual, strategic, and statistical considerations.
Journal of personality and social psychology, 51, 1173-1182.
Bishop, G., Spence, S. H., & McDonald, C. (2003) Can parents and teachers provide a
reliable and valid report of behavioral inhibition? Child devevelopment,74, 1899-1917. Bruni, O., Ottaviano, S., Guidetti, V., Romoli, M., Innocenzi, M., Cortesi, F. & Giannotti, F.
(1996). The sleep disturbance scale for children (SDSC). Construction and validation of an instrument to evaluate sleep disturbances in childhood and adolescence. Journal of sleep research, 5, 251-262.
Page 16 Pittsburgh sleep quality index: a new instrument for psychiatric practice and research.
Journal of psychiatric research, 28, 193-213.
Carskadon, M., Vieira, C., & Acebo, C. (1993). Association between puberty and delayed phase preference. Sleep, 16, 258-262.
Chelminski, I., Ferraro, F. R., Petros, T.V., & Plaud, J. J. (1999). An analysis of the
„„eveningness-morningness‟‟ dimension in „„depressive‟‟ college students. Journal of affective disorders, 52, 19-29.
Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd edition). Hillsdale, NJ: Erlbaum.
Curcio, G., Ferrara, M., & De Gennaro, L. (2006). Sleep loss, learning capacity and academic performance. Sleep medicine reviews, 10, 323-337.
Dahl, R. E. (1996). The impact of inadequate sleep on children‟s daytime cognitive function.
Seminars in pediatric neurology, 3, 44-50.
Drennan, M. D., Klauber, M. R., Kripke, D. F., & Goyette, L. M. (1991). The effects of depression and age on the Horne-Ostbergmorningness-eveningness score. Journal of affective disorders, 23, 93-98.
Ellis, L. K., & Rothbart, M. K. (2001). Revision of the early adolescent temperament
questionnaire. Poster presented at the 2001 biennial meeting of the society for research in child development. Minneapolis, Minnesota.
Fallone, G., Acebo, C., Arnedt, J. T., Seifer, R., & Carskadon, M. A. (2001). Effects of acute sleep restriction on behavior, sustained attention, and response inhibition in children.
Perceptual and motor skills, 93, 213-229. doi:10.2466/pms.2001.93.1.213. Gau, S. S., Shang, C., Merikangas, K. R., Chiu, Y., Soong, W., & Cheng, A. T. (2007).
Association between morningness-eveningness and behavioral/emotional problems among adolescents. Journal of biological rhythms, 22, 268-274. doi:10.1177/0748730406298447.
Giannotti, F., Cortesi, F., Sebastiani, R., & Ottaviano, S. (2002). Circadian preference, sleep and daytime behavior in adolescence. Journal of sleep research, 11, 191-199.
Goldstein, D., Hahn, C.S., Hasher, L., Wiprzycka, U.J., & Zelazo, P.D. (2007). Time of day, intellectual performance, and behavioral problems in morning versus evening type adolescents: Is there a synchrony effect? Personality and individual differences, 42, 431-440.
Page 17
Journalof theAmerican academyofchildandadolescent psychiatry, 40, 1337-1345. Gregory, A. M., Caspi, A., Eley, T. C., Moffitt, T. E., O´Connor, T. G., & Poulton, R. (2005).
Prospective longitudinal associations between persistent sleep problems in childhood and anxiety and depression disorders in adulthood. Journal of abnormal child psychology, 33, 157-163.
Gulliford, M. C., Price, C. E., Rona, R. J., & Chinn, S. (1990). Sleep habits and height at ages 5 to 11. Archives of disease in childhood, 65, 119-22.
Hoedlmoser, K., Kloesch, G., Wiater, A., & Schabus, M. (2010). Self-reported sleep patterns, sleep problems, and behavioral problems among school children aged 8–11 years.
Somnologie, 14, 23-31.
Hur, Y. M. (2007). Stability of genetic influence on morningness-eveningness: a cross
sectional examination of South Korean twins from preadolescence to young adulthood. Journal of Sleep Research, 16, 17-23.
Iglowstein, I., Jenni, O. G., Molinari, L., & Largo, R. H. (2003). Sleep duration from infancy to adolescence: reference values and generational trends. Pediatrics, 111, 302–307. doi:10.1542/peds.111.2.302.
Kerkhof , G.A. (1985). Inter-individual differences in the human circadian system: a review.
Biological psychology, 20, 82-112.
Kim, S., Dueker, G.L., Hasher, L., & Goldstein, D. (2002). Children's time of day preference age, gender and ethnic differences. Personality and individual differences, 33 ,1083-1090.
Lange, L. & Randler, C. (2011). Morningness-eveningness and behavioural problems in adolescents. Sleep and biological rhythms, 9, 12-18.
Lauderdale, D. S., Knutson, K. L., Yan, L. L., Liu, K., & Rathouz, P. J. (2008). Sleep
duration: how well do self-reports reflect objective measures? The CARDIA sleep study. Epidemiology, 19, 838-845.
Lockley, S. W., Skene, D. J., & Arendt, J. (1999). Comparison between subjective and actigraphic measurement of sleep and sleep rhythms. Journal of Sleep Research, 8, 175-183.
Liu, X., Sun, Z., Uchiyama, M., Shibui, K., Kim, K., & Okawa M. (2000). Prevalence and correlates of sleep problems in Chinese schoolchildren, Sleep, 23, 1053-1062. Morin, C. M. (1993). Insomnia: psychological assessment and management. New York:
Page 18 Natale, V., & Cicogna, P. C. (2002). Morningness-eveningness dimensions: is it really a
continuum? Personality and individual differences, 32, 809-816.
Ohayon, M. M., Carskadon, M. A., Guilleminault, C., & Vitiello, M. V. (2004). Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep, 27, 1255-1273. O´Malley, E. B., & O´Malley, M. B. (2008). School start time and its impact on learning
and behavior. In: A. Ivanenko (Ed.), Sleep and psychiatric disorders in children and adolescents (pp. 79.94). New York: Informa healthcare.
Paavonen, E.J., Almqvist, F., Tamminen, T., Moilanan, I., Piha, J., Räsänen, E., & Aronen, E.T. (2002). Poor sleep and psychiatric symptoms at school: an epidemiological study.
European child & adolescent psychiatry, 11, 10-17.
Paavonen, E. J., Porkka-Heiskanen, T., & Lahikainen, A. R. (2009). Sleep quality, duration and behavioral symptoms among 5–6-year-old children. European child & adolescent psychiatry, 18, 747-754. doi:10.1007/s00787-009-0033-8.
Petersen, A. C., Crockett, L., Richards. M., & Boxer, A. (1988). A self-report measure of pubertal status: reliability, validity, and initial norms. Journal of youth and adolescence, 17, 117-133.
Pilcher, J. J., & Huffcutt, A. I. (1996). Effects of sleep deprivation on performance: a meta- analysis. Sleep, 19, 318-326.
Preckel, F., Lipnevich, A. A., Schneider, A., & Roberts, R. D. (2011). Chronotype, cognitive abilities, and academic achievement: a meta-analytic investigation. Learning and individual differences, 21, 483-492.
Randler, C. (2008). Morningness-eveningness comparison in adolescents from different countries around the world. Chronobiology international, 25, 1017-1028.
Roenneberg, T., Kuehnle, T., Pramstaller, P. P., Ricken, J., Havel, M., Guth, A., & Merrow, M. (2004). A marker for the end of adolescence. Current Biology, 14, 1038–1039. Spruyt, K., O´Brien, L. M., Cluydts, R., Verleye, G. V., & Ferri, R. (2005). Odds, prevalence
and predictions of sleep problems in school-age normal children. Journal of sleep research, 14, 163-176.
Szymczak, J. T., Jasinska, M., Pawlak, E., & Zwierzykowska, M. (1993). Annual and weekly changes in the sleep-wake rhythm of school children. American sleep disorders association and sleep research society, 16, 433-435.
Page 19 characteristics of subjects able to extend their sleep beyond 10 hours. Sleep research, 26, 237.
Werner, H., LeBourgeois, M. K., Geiger, A., & Jenni, O. G. (2009). Assessment of
