Skip to content



1.1: Background
The relationship between 24-hour circadian rhythms and depression has not been well researched with those who prefer night activity and others who prefer day activity although Chelminski et al (1999) reported significantly more “evening-types” than “morning-types” among “depressive” college students.
1.2: Aims
The aim was to investigate if there was a relationship between depression and sleep and wake preferences and sleep propensity among students.
1.3: Method
Fifty undergraduate students at a college of higher education in South Wales completed two self-report questionnaires measuring the correlates.
1.4: Results
There was a significant negative correlation between “morningness” and depression (r(50) = -.263, p<0.05), no relationship between ““eveningness”” and depression (r(50) = .079, p<0.05) and a significant positive correlation between sleep propensity and depression (r(50) = .320, p<0.05).
1.5: Conclusions
“Morning-types" were less likely to suffer with depression. Future research would utilise a fuller version of the LOCI, with chronobiological data such as sleep diaries for a fuller profile and a wider variety of depression scales would be used to better measure depression.


“Early to bed, early to rise makes you healthy, wealthy and wise” and “the early bird catches the worm” are two maxims. Could they just be representative of a brand of folk psychology which we have come to accept as being factual but which actually varies considerably from person to person and may, in many cases, be totally inaccurate?
Does science or experience really draw the general truth that those people who rise early and go to sleep early are in better health, earn more money and are more intelligent than those people who go to sleep late and rise late?
Researchers with an interest in individual differences have been known to divide people by diurnal type — whether they prefer the morning (wake up early, go to bed early) or evening (go to bed later, get up later) as these individual personality types appear to have an effect on the results of experiments conducted at certain times of the day. For instance, “evening-types” had significantly higher intelligence scores than did the “morning-types” in a recent study (Roberts and Kyllonen, 1999) and “evening-types” reported psychological and psychosomatic disturbances more frequently and intensively than did “morning-types”, and showed more problems in coping with environmental and social demands in a separate study (Mecacci and Rocchetti, 1998).
A study of “depressive” college students by Chelminski et al (1999) discovered that there was a significantly higher incidence of “evening-types” than of “morning-types” among the depressive students.
Research examining various psychological correlates of circadian type (also known as diurnal preference) has been, over the years, quite expansive, although circadian variability in depression and psychological well-being has not been well characterised.
The term “circadian” means: “the near 24 hour physiologic rhythm that has been observed under free-running conditions, at every system level in nearly all plants and mammals, under near constant environmental conditions” (Brown, 1982, p 121). The assumption that exists that definite types of person correspond to diurnal preference (e.g. Kerkhof, 1982; Tankova, Adan and Buela-Casal, 1994; Roberts, Irvine and Kyllonen, 1998) has a long history with anecdotal evidence deriving from a variety of sources including Johnson’s “love of lying till noon” (Boswell, 1785) to modern versions of the “early bird” and the “night owl”. These were formally conceptualised as a trait, lying along a continuum that has come to be known as the “morningness-eveningness” M-E dimension, following Kleitman’s (1939/1963) research.
Correlations between M-E and various variables, including: age, gender, personality and caffeine consumption have been reported in a major review of the literature examining individual differences in circadian types (Tankova et al, 1994).
There is evidence that there may be a genetic reason why some people seem to be “night owls” and others “early birds”. A study by Mignot et al (1998) showed for the first time that there is a genetic component for “morningness” and “eveningness”. The 410 participants were asked to complete a Horne and Ostberg questionnaire to determine their “morningness-eveningness” preference. It was found that carriers of one genotype had lower Horne and Ostberg scores, indicating an increased preference for “eveningness”, while the other genotype scored significantly higher than the other group, indicating increased preference for “morningness”. It confirmed what researchers had suspected, that people with a specific variation of one particular gene, called the CLOCK gene, have slightly altered circadian rhythms. Mignot et al said: “People with altered circadian rhythms may not be ready to go to bed when society tells them to. And they may be getting out of bed too early or too late.” (1998, p 41).
Researchers hope that some day, humans may be able to test their genetic make-up to determine their healthiest schedule. Genetic reasons may explain why some people are not productive workers at 8am, and why others are not productive at 4.30pm. Ideally, says Mignot et al, “workers of the future will be able to adjust their schedules so as to optimize the time they spend at work.” (1998, p 53) Indeed, The findings of this study and continued research on this topic could have an important impact on insomnia research and therapy as well as work schedule organisation.
The effects of wake and sleep patterns have also been studied within the context of interpersonal relationships. For instance, married couples whose sleep and wake patterns were mismatched (an “evening person” married to a “morning person”) reported significantly less marital adjustment and more marital conflict, less time spent in serious conversation, less time spent in shared activities, and less frequent sexual intercourse than matched couples. There are important implications of these findings for premarital and marital counselling.
The “biological clock” is important in the structure of sleep and any study of chronobiology takes into account the fact that behavioural, psychological and biological variables all show a definite periodicity within a cycle length of 24 hours.
Genetic differences in individuals can also result in altered circadian period and this may be the foundation for “morningness-eveningness” preferences. Different personality profiles, too, appear to have an effect on these psychological correlates. Clinically depressed people have reported significantly more “eveningness” than age and sex matched controls and it has been suggested that this is not simply a characteristic of the depressive state, but rather reflects a premorbid trait or vulnerability.
The following Literature Review will help to explain the four key factors in the present study: the circadian phase, the genetic component, individual differences and depression, and will evaluate the empirical evidence which point to links between “eveningness-morningness” and these four factors.


2.1: “Eveningness-morningness” and the circadian phase
Psychological, behavioural and biological variables all show a definite periodicity with a cycle length of 24 hours. Body temperature, heart rate, blood pressure and hormone levels as well as mood, alertness, drowsiness and task performance all demonstrate circadian (the 24-hour cycle) effects. The rhythms tend to be consistent across individuals although individual differences in circadian rhythms have been observed and one of the most important has been "eveningness" and "morningness". Some people consistently prefer day activity while others prefer night activity (Freeman and Hovland, 1934; Kleitman, 1939) these diurnal types are known to differ in sleep-wake patterns, biological rhythms, preferences, affect and behaviours (Kerkhof, 1985).
Scientists have encountered substantial difficulties in deciding how to explain “morningness-eveningness” even though, intuitively, the difference between “morning-type” and “evening-type” people is clear. It has, for instance, been considered a personality dimension, such as introversion/extraversion (Mecacci et al, 1997).
The connection between “eveningness-morningness” and the 24-hour biological clock has often been questioned. In recent years, however, numerous indications have been found that there is such a connection and that the study of “morningness-eveningness” deserves a place within the field of chronobiology.
The "biological clock", which is situated in the suprachiasmatic nuclei of the brain, generates a circadian rhythm that modulates a multitude of bodily functions. Under normal circumstances, this rhythm has a period of 24 hours and is reflected in, for instance, the daily variation of body temperature. The circadian phase is the time (relative to an arbitrary origin) at which the circadian rhythm of a variable (such as body temperature) reaches a particular state (i.e. the daily maximum or minimum). It is an important parameter, for it expresses the timing of a circadian rhythm relative to the time of day.
When considering the circadian rhythmicity (whether for research purposes or for clinical applications), it is important to know the variation that can be found in this parameter. It appears that there are inter-individual differences in the circadian phase of most variables one can think of. For instance, consider the variation in the timing of peak alertness among students. Generally, people are categorised with regard to the overall circadian phase of their behavioural variables such as peak alertness, preferred work hours, and timing of sleep. These are called “morning-types” or “evening-types” accordingly.
By means of constant routine experiments, the endogenous nature of “morningness-eveningness” became apparent. “Morning-types” and “evening-types” differed in the phase of the circadian rhythm of body temperature. On average, the biological clock of “evening-types” lagged behind by 2.1 hours with respect to that of morning-types (Dawson et al, 1992). This result has been replicated by Hall et al (1997).
In the literature, inconsistent results have been obtained concerning the question whether the circadian timing of sleep (i.e. its timing with respect to the circadian rhythmicity) depends on “morningness-eveningness”. It has been shown that the structure of sleep (the distribution of slow wave sleep and REM sleep) is modulated by the circadian timing of sleep (Czeisler et al, 1980).

2.2: “Eveningness-morningness” and the genetic component
Recent reports on genetic differences between morning-types and evening-types (Mignot et al, 1998) suggest that genetic differences resulting in altered circadian period may be the basis of “morningness-eveningness” preferences. Blood samples provided DNA that showed the existence of genes in the same location that occur in more than one form. It was found that carriers of one genotype had lower “eveningness-morningness” scores, indicating an increased preference for “eveningness”, while the other genotype scored significantly higher than the other group, indicating increased preference for “morningness”. This study showed for the first time that there is a genetic component for “morningness” and “eveningness”.
The work which has established that there are genetic differences between “morning-types” and “evening-types” has important implications for understanding circadian rhythm sleep disorders and could lead to improved work schedules, with employees being tested for genetic make-up. One area, however, where the “morningness-eveningness” dimension has not been exhaustively researched is in the area of depression.

2.3: “Eveningness-morningness" and individual differences
"Morning-types" and "evening-types" appear to be characterised by different personality profiles (Adan, 1992; Matthews, 1988; Mecacci et al, 1991; Rocchetti et al, 1986; Wilson, 1990). "Evening-types" are more irregular in mealtimes, consume more alcohol and coffee, and are more habitual smokers than "morning-types". (Costa et al, 1989; Folkard and Monk, 1985; Mecacci and Zani, 1983).
In a study by Mecacci and Rocchetti (1997), "evening-types" (especially male) showed symptoms of difficulty in coping with environmental and social demands, and such individuals may exhibit lifestyles which are generally associated to stress and risk for cardiovascular disease. It has been reported that gender differences need to be investigated further. It was found that interactions between circadian type and gender might be observed when data were collected not only over one day, but over one month (Mecacci et al, 1991), and in females, monthly variations of activation and mood, associated to the menstrual cycle may represent another variable affecting the stress reactivity.
One of the most commonly cited differences is a positive correlation between level of "eveningness” and extraversion (Colquhoun, 1982; Eysenck, 1982; Folkard and Monk, 1983; Kirkalldy, 1984; Mecacci et al, 1986; Wilson, 1990).
Extraverts tend to be "evening-types" and introverts tend towards "morningness". "Evening-types" were found to be more pessimistic than "morning-types" in a study by Levy, 1985. Some correlational studies have suggested that "eveningness" is related to higher neuroticism. However, Tankova et al (1994), in their review of studies that have examined the relationship between circadian typology and other individual differences variables, concluded that neuroticism and psychotism are not associated with "morningness-eveningness".
Mecacci et al (1986) found that "morning-types" had significantly higher scores on a neuroticism scale and "evening-types" had significantly higher scores on a psychotism scale. Wilson (1990) reported the same relationship between psychotism and "eveningness".
There is considerable evidence now to point to an association between age and "eveningness-morningness". It is typical for older people to tend more towards "morningness" than "eveningness" in their personalities (May et al, 1993; Mecacci et al, 1986; Monk et al, 1991). It is not, however, known whether this is due to individual preferences or to work schedule. For instance, sleep-wake diary data of “morning” and “evening-types” in student and worker samples showed that the acquisition of a regular job (usually from 9am to 5pm) seems to induce a change in sleep-wake behaviour. This is particularly relevant in this study as students are more likely to be able to adapt their study schedule to their natural preferences, whereas older people in work have to adjust themselves to the demands of working in the morning and early afternoon. As students are not forced to develop morning activity, some concluded that in cases where students do prefer morning activities to evening activities then it is determined endogenously (Adan and Almirall, 1991; Tankova et al, 1994).

2.4: “Eveningness-morningness” and depression
Depression, or Unipolar Affective Disorder, is widely considered to be the common cold of mental illness (Seligman, 1975). It is estimated that the lifetime prevalence rate for the general population is between four and five per cent (Weissman, Leaf and Tischler, 1988).
The depressed person experiences a general slowing down and loss of energy and enthusiasm for life. Although it is characterised as a disorder of mood, there are actually four sets of symptoms: these are emotional, cognitive, motivational and physical symptoms. Most depressive episodes are of relatively short duration. Depressed people gradually recover, with or without treatment. A distinction that is deeply embedded within psychiatric thinking is that between endogenous (“from the inside”) and reactive or exogenous (“from the outside”) depression – also classified as psychotic and neurotic depression respectively. It is worth noting that influences on the circadian rhythmicity originating from within the body are called endogenous and those originating from outside are called exogenous. This distinction in depression, however, is more controversial and endogenous is now used to describe a certain cluster of symptoms and not to refer to how the depression was caused (Williams and Hargreaves, 1995)
Clinically depressed patients reported significantly more "eveningness" than age and sex-matched controls (Drennan et al, 1991) and it was concluded that it is possible that the increased "eveningness" in depressed patients is not simply a characteristic of the depressive state, but rather reflects a premorbid trait or vulnerability.
Seasonal Affective Disorder (SAD) was originally conceptualised as relating to seasonal rhythms and was treated with bright-light exposure therapy to extend dawn and dusk (Lewy et al, 1982). It was suggested that bright light therapy may be effective because some sufferers may have an advanced or delayed circadian rhythm as possibly indicated by delayed or advanced melatonin secretion. Lewy et al (1987) hypothesised that most winter-time depressives have abnormally delayed circadian rhythms. Indeed, SAD patients exhibited more "eveningness" than controls in a study by Rosenthal and Blehar (1989).
The hormone melatonin is important in the internal maintenance of biological rhythms (Wetterburg, 1985). Melatonin, closely related to the neurotransmitter serotonin, is secreted by the pineal gland mainly during the hours of darkness. It appears to convey knowledge about the external environment to the body clock (Tamarkin et al, 1985). Zetin et al (1987) suggest that it may be a useful neuroendocrine indicator of affective disorders. Rao and Mager (1987) reported that the dramatic reduction of the nocturnal rise of melatonin observed in depression may alter the coupling processes between the pineal gland and other endocrine functions, thus promoting internal dissociations between different circadian rhythms and that the manipulation of these processes may be beneficial for depression. Tricyclics, for instance, have been shown to increase the nocturnal secretion of melatonin in depressed patients, and the pharmacological stimulation of the nocturnal secretion of melatonin has been shown to have antidepressant effects (Souetre et al, 1988).
Studies by Steiner et al (1987) and Kripke et al (1987) suggested that a phase shift and a change in circadian rhythms of melatonin in the retina may be caused because of a biochemical defect in depressive people. This phase shift then alters the sensitivity of the retina to light, which in turn desynchronises all other biological rhythms.

2.5: Aims and hypotheses
The aims of this study were to investigate if there was a relationship between sleep-wake preference and propensity for sleep debt and depression in students. The hypotheses and null hypotheses, listed below, were all one-tailed
There will be a significant negative correlation between "morningness" and higher levels of depression in students.
There will be a significant positive correlation between “eveningness” and higher levels of depression in students.
There will be a significant positive correlation between propensity for sleep debt and higher levels of depression in students.
There will be no significant negative correlation between “morningness" and higher levels of depression in students.
There will be no significant positive correlation between “eveningness” and higher levels of depression in students.
There will be no significant positive correlation between propensity for sleep debt and higher levels of depression in students.


This research lent itself to self-administered questionnaires since anonymity and confidentiality of information given by participants were considered necessary attributes when investigating a sensitive issue such as depression. In order to maximise the collection of data within time and financial constraints, the use of questionnaires as a measurement tool is recommended (Oppenheim, 1992). Other survey methods of data collection, such as the mailing of questionnaires or interviewing, were disregarded since response rates are traditionally low and distribution is costly.
It was decided that an observation study was unsuitable as it would have caused ethical problems regarding undisclosed observation or intervention of any kind, It would have been impractical to replicate, and it would have been difficult to control other variables, which might have influenced the study. A qualitative approach, using interviews and/or diary observation or case studies was also considered but it was decided that these can often involve recall of earlier history, and are therefore unreliable. It was also decided that a close relationship between the participant and the researcher could introduce bias, and a more limited sample, which usually occurs when this approach is taken, would have lacked generalisability. It was also considered too time-consuming and expensive.

The study used a single condition quasi-experimental survey design, the independent variables being “eveningness”” or “morningness” (whether a person is a “lark” or an “owl”), propensity for sleep debt and the dependent variable being their levels of depression.

A total of 50 people participated in the study. They were recruited using opportunity sampling through a college of higher education in South Wales. There was no exclusion criterion.

Two questionnaires and two demographic questions establishing the age and sex of the participants were employed. The Lark-Owl (Chronotype) Indicator (Roberts et al, 1999) was used to measure levels of “morningness” and “eveningness” and to measure propensity for sleep debt and a 13 item sub-scale of the Symptom CheckList (Problems and Complaints relating only to depression, rather than other disorders), was derived from the SCL-90-R (Derogatis, 1977).
The Lark-Owl (Chronotype) Indicator (see Appendix 2) is a self-report psychometric test, using a six-point Likert scale. The complete inventory measures three dimensions of chronotype: “morningness” “eveningness” and “propensity for sleep debt”, which reflects an individual’s propensity for catching up on lost sleep. The LOCI protocol has been validated in four studies totalling nearly 1,800 participants. It is regarded as a more reliable scale than its popular precursor, the Horne and Ostberg Questionnaire because it is based on both rational and EFA approaches; includes equal numbers of “eveningness” and “Morningness” questions; possesses superior psychometric properties; and has both peer and self-report protocols (which provide excellent construct validation, see Costa and MacCrae, 1991).
The Symptom Checklist (see Appendix 3) is a 5 point Likert scale measuring depression. This measure is a widely used and well validated tool in clinical use. For the purposes of this study, a 13 item sub-scale (‘Problems and complaints’, relating only to depression, rather than other disorders) was derived from the SCL-90-R. This reduced the bulk of the survey and provided a reasonable measure of depression.
A brief demographic survey constituted the final part of the questionnaire since such information is generally perceived by participants as less intrusive and less taxing to disclose (Fife-Schaw, 1995, in Breakwell, Hammond and Fife-Schaw).
Questions requiring information regarding age and sex were included in order to obtain the general features of the sample.

A pilot study was conducted involving 13 participants in order to determine item ambiguity or objections to content and to monitor any inconvenience or embarrassment caused to participants. Validity and reliability issues, however, were not piloted as they had previously been addressed by the creators of both scales used, prior to their introduction.
The results of the pilot study indicated the need for a number of alterations and exclusions after feedback forms from participants (Appendix 1) were analysed.
The forms contained seven open-ended questions with one asking directly how it could have been improved. The main recommendation was to reduce the number of pages in order to encourage participants to co-operate fully and make it more convenient for participants.
The SCL-90-R questionnaire was refined and printed on one sheet of paper rather than two, after some pilot study participants pointed out that the two page format caused them inconvenience and could lead to some participants skipping some questions or giving answers without really thinking about the question.
Similarly, the LOCI was refined and printed on one page after some pilot study participants pointed out that the three page format caused them some inconvenience and could also lead to some participants skipping some questions or giving answers without really thinking about the question.
A recommendation to have colour in the questionnaire in order to make it “less clinical” was noted but the prohibitive cost of putting colour in the questionnaires prevented this from being done.
Critical feedback about the questions asked in the two scales were again noted but no refinements were made to the scales since these issues had previously been addressed by the creators, prior to their introduction.

Ethical approval from the faculty ethics panel was sought and granted with no reservations, and senior lecturers at the college of higher education gave their permission before potential participants were approached and asked to participate.


The nature and object of the research was discussed with senior lecturers at a college of higher education in South Wales and permission was granted for the researcher to attend lectures at the convenience of the college.
The researcher introduced himself to participants and they were subsequently informed that the purpose of the research was to investigate diurnal preference and its relation to depression for a final year project. The students were assured of the confidential and anonymous nature of the study and that participation was entirely voluntary. Each participant was thanked for their help and any questions about the study were answered by the researcher.

The median LOCI scores were correlated with the corresponding SCL-90-R scores in order to investigate possible relationships between variables. Spearman’s rho analysis was applied. As more correlations were undertaken in order to correlate the total LOCI score with each individual SCL-90-R score, the probability of receiving significant data was increased. Therefore adjustment was required to the probability level of a significant statistic. The simplest method of adjusting the figure is the highly conservative Bonferroni adjustment (Holm, 1979, Sidak, 1967, cited in Breakwell, Hammond and Fife-Schaw, 1995).
All data were analysed using SPSS (Statistical Package for the Social Sciences) 7.5 for Windows ‘95.


4.1: Sample
A total of 50 students participated in the study, 36 females (72 per cent) and 14 males (28 per cent).

Figure 4.1: Sex of sample

Of these, 43 were aged 18 to 30 (86 per cent) and 7 were aged more than 30 (14 per cent). The response rate was 100 per cent.
Figure 4.2: Age of sample

4.2: Study scores on the SCL-90-R
The SCL-90-R was scored using a Likert-type scale. Those that were “definitely depressed” had a high score, those that were “definitely not depressed” had a low score and those that were “possibly depressed” scored in the mid-range. The median score was 26, the range of scores was 13 to 65. The cut-off points were 13-30 “definitely not depressed”, 31-47 “possibly depressed”, and 48-65 “definitely depressed”.
Table 4.2: Frequency of scores for SCL-90-R
40 10 0
80% 20% 0%

4.3: Correlations between LOCI and SCL-90-R
All data in the study was ordinal, therefore the measure of central tendency used was the median and the measure of dispersion was the minimum and maximum scores. Scores were correlated using the Spearman’s Rank Correlation Coefficient, as the data was ordinal. Correlations undertaken were between levels of depression, as measured by the SCL-90-R, and levels of “eveningness” “morningness” and propensity for sleep debt, as measured by the LOCI.
The correlation between "morningness" and scores on the depression scale was significant (r(50) = -.263, p<0.05) so the alternative hypothesis H1 could be accepted. The correlation between “eveningness” and scores on the depression scale was not significant (r(50) = 0.079, p<0.05) so the null hypothesis H02 could not be rejected. The correlation between propensity for sleep debt and scores on the depression scale was significant (r(50) = 0.320, p, B., (Ed), Biological Rhythms, Sleep and Performance. John Wiley and Sons, Chichester.
Costa, G., Lievore, F., Ferrari, P., and Gaffuri, E., (1989). Usual meal times in relation to age, sex, work activity and morningness-eveningness. Chronobiologica, 14, 383-391.
Czeisler, C. A., Silva, E. J., Rimmer, D. W., and Duffy, J. F., (1999). Correlation of Intrinsic circadian period with morningness-eveningness in young men. Personality and individual differences, 26, 231-242.
Derogatis, L., R., (1977). SCL-90-R: Administration, scoring and procedures manual 1 for the R(evised) version. John Hopkins University School of Medicine, Clinical Psychometrics Unit.
Drennan, M., D., Klauber, M., R., Kripke, D., F., Goyette, L., M., (1991). The effects of age on the Horne and Ostberg morningness-eveningness score. Journal of Affective Disorders, 23, 93-98.
Eysenck. M., W., (1982). Endogenous determinants of arousal. In: Eyesenck, M., W., (Ed.) Attention and arousal. Springer-Verlag, New York.
Fife-Schaw, C. (1995). Questionnaire design. In Breakwell, G. M., Hammond, S. and Fife-Schaw, C. (Eds.), Research Methods in Psychology. London, Sage.
Folkard, S. and Monk, T. (1983). Chronopsychology: Circadian rhythms and human performance. In: Gale, A. and Edwards, J. (Ed.), Physiological correlates of human behaviour. Academic Press., London.
Folkard, S. and Monk, T. (Eds.). (1985). Hours of work: Temporal factors in work scheduling. New York: Wiley.
Freeman, G. and Hovland, C., (1934). Diurnal variations in performance and related physiological processes. Psychological Bulletin, 31, 777-799.
Horne, H., J., and Ostberg, O., (1976). A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. International Journal of Chronobiology, 4, 97-110.
Kerkhof, G., A., (1985). Inter-individual differences in the human circadian system. A Review. Biological Psychology, 20, 83-112.
Kirkaldy, B. D., (1984). Performance and circadian rhythms. European Journal of Apllied Physiology, 52, 375-379.
Kleitman, N. (1939/1963). Sleep and wakefulness. Chicago, IL: University of Chicago Press.
Kripke, D. F., Mullaney, D. J., Atkinson, M. S., Wolf, C. (1987). Circadian rhythm disorders in manic depressives. Biological Psychology, 13, 720-724.
Levy, D. A., (1985). Optimism and pessimism: relationship to circadian rhythms. Psychological Reports, 57, 1123-1126.
Lewy, A. J., Sack, R. L., Singer, C. M., (1985). Treating phase typed chronobiologic disorders using appropriately timed bright artificial light. Psychopharmocological Bulletin, 21, 368-372.
Lewy, A. J., Sack, R. L., Singer, C. M., (1987). Antidepressant and circadian phase-shifting effects of light. Science, 235, 352-354.
Matthews, G. (1988). Morningness-eveningness as a dimension of personality: Trait, state and psychophysiological correlates. European Journal of Personality, 2, 277-293.
May, C. P., Hasher, L. and Stoltzfus, E. R., (1993). Optimal time of day and the magnitude of age differences in memory. Psychological Science, 4, 326-330.
Mecacci, L., Scaglione, R., and Vitrano, I., (1991). Diurnal and monthly variations of temperature and self-reported activation in relation to sex and circadian typology. Personality and Individual Differences, 16, 671-684.
Mecacci, L., and Rocchetti, G., (1998). Morning and evening types: Stress related personlity aspects. Personlity and Individual Differences, 25, 537-542.
Mignot, E., Katzenberger, D., Lin, L., Young, T., Finn, L., (198). The human CLOCK gene as a predictor of morningness-eveningness preference in adults. Sleep, 13, 234-240.
Monk, T. H., Reynolds, C. F., and Buysse, D. J., (1991). Circadian characteristics of healthy 80-year-olds and their relationship to objectively recorded sleep. Journals of Gerontology, 45, M171-M175.
Openheim, A. N., (1992). Questionnaire design. Interviewing and attitude measurement. London: Pinter.
Rao, M. L., and Mager, T. (1987) Influence of the pineal gland on the pituitary function in humans. Psychoendicronology, 12, 141-147.
Roberts, R. D., and Irvine, S., (1999). Construction and validation of the lark-owl (chronotype) indicator (LOCI): status report. Unpublished manuscript.
Roberts, R. D., and Kyllonen, P. C., (1999). Morningness-eveningness and intelligence: Early to bed early to rise will make you anything but wise! Personality and individual differences, 27, 1123-1133.
Roberts, R. D., Irvine, S., and Kyllonen, P. C., (1998). Personlity and circadian type: a Review and empirical investigation. Unpublished manuscript.
Rosenthal, N. E., and Blehar, M. C., (1989). Seasonal affective disorders and phototherapy. Guilford Press. New York.
Seligman, M. E. P., (1975) Helplessness: On depression, development and death. San Francisco: W H Freeman.
Soetre, E., Salvati, E., Belugou, J. L., Roberts, P., Brunet, G., and Darcourt, G., (1988). Antidepressant effect of 5-methoxypsoralen: A preliminary report. Psychopharmacology, 95, 430-431.
Steiner, M., Werstuik, E. S., and Seggie, J., (1987). Dysregulation of neuroendocrine crossroads: depression, circadian rhythms and the retina — a hypothesis. Progress in Neuro psychopharmacology and Biological Psychiatry, 11, 267-278.
Tankova, I., Adan, A., and Buela-Casal, G., (1994). Circadian typology and individual differences. A Review. Personality and Individual Differences, 16, 671-684.
Weissman, M. M., Leaf, P. J., and Tischler, G. L., (1988). Affective disorders in five United States communities. Psychological Medicine, 18, 141-153.
Wilson, G. D., (1990). Personality, time of day and arousal. Personality and Individual Differences, 11, 153-168.
Zetin, M., Plotkin, S., and Urbancheck, M., (1987). Melatonin in depression. Psychiatric Annals, 17, 676-681.

Appendix 1: Pilot study data

Appendix 2: The Lark-Owl (Chronotype) Indicator (LOCI)

Appendix 3: The SCL-R-90

This questionnaire will ask you about how you feel about your life. You will be presented with a statement and asked to rate how strongly you agree or disagree with this statement. Please respond by underlining a number which best reflects your level of agreement/disagreement with that statement.

For example:
Oranges are my favourite fruit
Strongly agree 1 2 3 4
— 5 6 7 Strongly disagree

Please note that the poles of “agree” and “disagree” lie at the opposite end of the scale upon alternate questions. Please try to answer all questions quite quickly without thinking.

My life is running over with exciting good things
Strongly agree 1 2 3 4 5 6 7 Strongly disagree

I often seem to change my main objectives in life
Strongly disagree 1 2 3 4 5 6 7 Strongly agree

My life is in my hands and I am in control of it
Strongly agree 1 2 3 4 5 6 7 Strongly disagree

Some people are very frightened of death but I am not
Strongly disagree 1 2 3 4 5 6 7 Strongly agree

I think about the ultimate meaning of life
Strongly agree 1 2 3 4 5 6 7 Strongly disagree

I hope for something exciting in the future
Strongly disagree 1 2 3 4 5 6 7 Strongly agree

I feel that the greatest fulfilment of my life lies yet in the future
Strongly agree 1 2 3 4 5 6 7 Strongly disagree

Life to me seems very exciting
Strongly disagree 1 2 3 4 5 6 7 Strongly agree

I feel the lack of and need to find a real meaning and purpose in life

Strongly agree 1 2 3 4 5 6 7 Strongly disagree

I determine what happens in my life
Strongly disagree 1 2 3 4 5 6 7 Strongly agree

I am generally less concerned about death than those around me
Strongly agree 1 2 3 4 5 6 7 Strongly disagree

I am seeking a meaning, purpose or mission for my life
Strongly disagree 1 2 3 4 5 6 7 Strongly agree

Appendix 4: The data matrix

Appendix 5: Frequencies data

Appendix 6: Correlation data

Word count

Abstract 180 words

Introduction 2,736 words

Method 1,149 words

Results 782 words

Discussion 2,378 words

Total 7,498 words