Journal of Psychosomatic Research 63 (2007) 157 – 166
Psychological and health-related quality of life factors associated with insomnia in a population-based sampleB Me´lanie LeBlanca,b, Simon Beaulieu-Bonneaua,b, Chantal Me´rettec,d, Jose´e Savarda,e, Hans Iversb, Charles M. Morina,b,4 a´
Ecole de psychologie, Universite´ Laval, Que´bec, Canada Centre d’e´tude des troubles du sommeil, Centre de recherche Universite´ Laval-Robert-Giffard, Que´bec, Canada c Centre de Recherche Universite´ Laval-Robert-Giffard, Que´bec, Canada d De´partement de Psychiatrie, Universite´ Laval, Que´bec, Canada e Centre de recherche en cance´rologie de l’Universite´ Laval, l’Hoˆtel-Dieu de Que´bec, Que´bec, Canada Received 13 June 2006
Abstract Objective: This study examined the relationship of psychological and health-related quality of life variables to insomnia in a population-based sample. Methods: Data were derived from a longitudinal epidemiological study assessing the natural history of insomnia. The present results are based on the first of four postal evaluations conducted over a 2-year period. Participants (n=953) completed questionnaires assessing sleep, psychological and personality variables, and health-related factors. Participants were categorized into three sleep status subgroups using an algorithm based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision and International Classification of Diseases, 10th Edition diagnostic criteria for insomnia: (1) insomnia syndrome (n=147), (2) insomnia symptoms (n=308), and (3) good sleepers (n=493). Results: Compared to individuals with insomnia symptoms and good sleepers, individuals with insomnia syndrome presented lower quality of
life and higher scores on measures of depression, anxiety, neuroticism, extraversion, arousal predisposition, stress perception, and emotion-oriented coping. The same pattern was observed for individuals with insomnia symptoms in comparison with good sleepers. An ordinal logistic regression analysis showed that the presence of a past episode of insomnia, higher depressive symptoms, and lower scores on the 12-item Short Form Health Survey vitality and role physical subscales were the most useful variables to predict subgroups membership. Conclusion: The findings indicate that insomnia is associated with increased psychological symptomatology and perceived stress, higher predisposition to arousal, and more impairment of health quality. Longitudinal follow-ups are now being conducted to assess the relative contribution of those variables in the development and natural course of insomnia. D 2007 Elsevier Inc. All rights reserved.
Keywords: Associated factors; Correlates; Epidemiology; Insomnia; Sleep
Introduction Several epidemiological studies have been conducted to document the prevalence and correlates of insomnia. An B
This research was supported by a Canadian Institute of Health Research grant (#42504). 4 Corresponding author. E´cole de psychologie, Universite´ Laval, Que´bec, Canada G1K 7P4. Tel.: +1 418 656 2131x3275; fax: +1 418 656 5152. E-mail address: [email protected]
(C.M. Morin). 0022-3999/07/$ – see front matter D 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jpsychores.2007.03.004
estimated 30% of the adult population presents insomnia symptoms, and about 5–10% are affected by an insomnia syndrome [1–3]. Epidemiological studies have also demonstrated that prevalence rates increase with age and are higher among women, the unemployed, unmarried, and those with lower socioeconomic status [1,4–9]. In addition to sociodemographics, higher levels of depressive and anxiety symptoms have consistently been associated with insomnia . Individuals with insomnia also report more medical problems (e.g., arthritis, vascular disease),
M. LeBlanc et al. / Journal of Psychosomatic Research 63 (2007) 157 – 166
an increased use of medications, drugs, and alcohol and more frequent personal history of insomnia compared to good sleepers [6,10–15]. Most epidemiological studies examining insomnia correlates have restricted their investigation to depression, anxiety, and specific health problems [1,4–15]. To our knowledge, none has explored other variables (e.g., personality, arousability) that may be involved in the etiology of insomnia in the general population. For instance, in clinical samples, the personality patterns of individuals with insomnia have been characterized by the presence of neurotic traits, inhibition of emotions, rumination, and inability to discharge anger outwardly [16–20]. Individuals with insomnia have also been described as having fewer adaptive coping skills, relying more on emotion-oriented coping strategies than problem-solving strategies, and reporting lower feelings of mastery [21–23]. A higher arousability (i.e., physiological, cognitive, and emotional) during the day, at bedtime and at night has also been associated with insomnia [22–25]. Studies have shown that individuals with insomnia are more emotionally reactive, more alert and vigilant, and experience more intrusive thoughts than good sleepers [21,26–28]. Besides psychological factors, reduced quality of life has been associated with insomnia in population-based samples [29,30]. Finally, individuals with insomnia tend to report higher rates of family history of insomnia than good sleepers [31–33]. With the exception of one study on quality of life , results from clinical samples have never been replicated to the general population. Studies of insomnia correlates have generally considered single factors separately. Examining several factors simultaneously in the same sample can provide a more precise and exhaustive description of the profile of individuals with insomnia compared to that of good sleepers. Moreover, most studies that documented correlates of insomnia have relied on treatment-seeking individuals recruited from sleep clinics. Such studies, while valuable, are restricted to describing a single group of individuals with chronic insomnia [16,17,31], or when a comparative group of good sleepers is included, it is typically based on a convenience sample not drawn from the same population [18,20–22]. In addition, there has been no systematic investigation of the characteristics (e.g., personality, depression, and anxiety symptoms) of individuals with insomnia symptoms only (i.e., who do not fulfill all the diagnostic criteria of insomnia, although they represent approximately 30% of the general population) [1,2]. Consequently, the relationship between insomnia correlates and less severe or transient insomnia remains unknown. For instance, it is not known whether the higher levels of depressive and anxiety symptoms usually observed in individuals with an insomnia syndrome are also noticeable in individuals with insomnia symptoms. The investigation of these factors in individuals with less severe insomnia could guide the development of effective early intervention programs to
prevent the development of chronic insomnia and subsequent mental health disorders. The objective of the present study was to examine the relationship between insomnia and psychological and healthrelated quality of life factors in a population-based sample, through a comparison of subgroups of individuals with insomnia symptoms, insomnia syndrome, and good sleepers.
Methods Study context and sample selection Data from this study are derived from a larger epidemiological study conducted in the province of Quebec, Canada. The study began with a telephone survey, carried out by a professional pool firm . The sample consisted of French-speaking residents of the province of Quebec, 18 years and older. Sample selection involved two procedures: (1) random digit dialing method, which generates geographically stratified phone numbers, and (2) the Kish method , to identify the individual to be interviewed in each household. These methods ensure that the sample is representative of the target population. At the conclusion of the telephone interview, participants were asked if they wanted to take part in the longitudinal phase of the study, which involved completion of four postal evaluations over a 24-month period. The first evaluation was conducted 1 month after the telephone interview. The remaining three postal evaluations were conducted, respectively, 6, 12, and 24 months after the first evaluation. Data from the first postal evaluation only are reported in the present study. Participants and procedure Of the 5991 persons solicited, a total of 2001 (33.4%) respondents completed the telephone interview, and 1467 (73.3%) of them accepted to take part in the longitudinal study. Of this number, 105 were excluded because they reported the presence of a sleep disorder other than insomnia, the only exclusion criterion of the study. The first postal evaluation was mailed to 1362 participants, who were asked to return the completed questionnaire within a 2-week period. Reminder telephone calls were made afterwards for those who had not yet returned the measures. Response rate was 73.2%, with 997 participants having returned the completed measures for which they received a $25 monetary compensation. Of those, 44 additional participants were excluded because they reported the presence of another sleep disorder on the questionnaire, which was not reported at the telephone interview. The final sample included 953 participants. Sleep status groups Participants were classified in three groups according to an algorithm based on a combination of insomnia diagnostic
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criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IVTR) , the International Classification of Diseases, 10th Edition (ICD-10) , and on the utilization of sleeppromoting products (prescribed and over-the-counter). Responses from the Insomnia Severity Index (ISI)  and the Pittsburgh Sleep Quality Index (PSQI)  and from questions on sleep-promoting medication use were used to evaluate the presence or absence of each criterion. The three sleep status groups were defined as follows: !
Insomnia syndrome. Participants in this group met all the diagnostic criteria for insomnia. They were dissatisfied with their sleep [i.e., dissatisfied (3) or very dissatisfied (4) on a 0–4 scale] and presented symptoms of initial, maintenance, or late insomnia at least three nights per week for a minimum duration of 1 month. Psychological distress or daytime impairment related to sleep difficulties was also reported by those individuals [i.e., much (3) or very much (4) on 0–4 scales]. Finally, if prescribed medication was used as a sleep-promoting agent at least three nights per week, participants were automatically classified in the insomnia syndrome group whether or not they presented symptoms of initial, maintenance or late insomnia. Insomnia symptoms. Participants classified in this group presented symptoms of initial, maintenance or late insomnia at least three nights per week, without fulfilling all the diagnostic criteria of an insomnia syndrome (i.e., they could be satisfied with their sleep, not report distress or daytime consequences, or their sleep difficulties could last for b1 month). Also included in this group were individuals dissatisfied with their sleep quality but without symptoms of initial, maintenance or late insomnia. Lastly, participants using prescribed medication to promote sleep less than three nights per week or over-the-counter medication at least one night per week were automatically classified in this group. Good sleepers. These participants were satisfied with their sleep [i.e., very satisfied (0), satisfied (1), or neutral (2) on a 0–4 scale], did not report symptoms of initial, maintenance, or late insomnia and did not use prescribed or over-the-counter medication as a sleep-promoting agent.
Measures Several measures were used for the purpose of the present study. These included French–Canadian versions of validated self-report measures, as well as questions developed specifically for this study, covering four general domains: sleep, physical health and health-care service utilization, coping and life events, and mood and personality. Two sleep questionnaires (ISI and PSQI) [37,38] were
used to classify participants in the three sleep status groups and to describe the sample. All other measures were used to derive dependent variables. Sleep measures The ISI  is a seven-item questionnaire assessing the nature, severity, and impact of sleep difficulties. Dimensions are severity of sleep onset, sleep maintenance, and early morning awakening problems; sleep satisfaction; interference of sleep difficulties with daytime functioning; noticeability of sleep problems by others; and distress caused by the sleep difficulties. A five-point Likert scale (b0Q=not at all, b4Q=extremely) is used to rate each of these items, yielding a total score ranging from 0 to 28. Scores can be classified into four severity categories: absence of insomnia (0-7), subthreshold insomnia symptoms (8–14), moderate insomnia (15–21), and severe insomnia (22–28). The ISI has adequate psychometric properties and is sensitive to measure treatment outcome . The French–Canadian version of the questionnaire has good internal consistency, test–retest reliability and convergent validity (r=.65 when comparing with sleep diary) . The PSQI  is a 19-item questionnaire evaluating sleep quality and disturbances over a 1-month time interval. The first four items are open questions, whereas items 5 to 19 are rated on a four-point Likert scale. Individual items’ scores yield seven components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep-promoting medication, and daytime dysfunction. A total score, ranging from 0 to 21, can be obtained by adding the seven component scores. A score higher than 5 suggests poor sleep quality. Psychometric properties of the PSQI are adequate, especially regarding the diagnostic sensitivity (89.6%) and specificity (86.5%) for psychophysiological insomnia. The validated French– Canadian version has adequate psychometric properties as well . Sleep-promoting products (i.e., prescribed and over-thecounter medications) utilization was assessed with the following questions: bDuring the past month, how many nights per week have you taken prescribed medication to help you sleep?Q and bDuring the past month, how many nights per week have you taken over-the-counter medication (e.g., Nytol, Sominex) to help you sleep?Q Personal and familial histories of insomnia were measured with the following questions: bIn the past, have you ever experienced insomnia a few days per week for more than 1 month? (yes/no),Q bIs a member of your immediate family (parents, children, brothers, sisters) currently experiencing sleep difficulties? (yes/no),Q and bHas a member of your immediate family (parents, children, brothers, sisters) ever experienced sleep difficulties? (yes/no).Q For those answering in the affirmative, follow-up questions asked for identifying the family member(s) and the type of sleep problem (insomnia, excessive daytime sleepiness, sleep apnea, restless legs or periodic limb movements, etc.). A
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family history of insomnia was defined as a report of at least 1 parent or sibling with past or current insomnia. Psychological measures The Beck Depression Inventory II (BDI-II)  contains 21 items rating depressive symptoms experienced during the past 2 weeks on a four-point Likert scale. A total score (ranging from 0 to 63) is derived with a higher score suggesting a higher depressive symptomatology. The cutoff score for depressive symptoms of moderate severity is 20 . The psychometric properties of the French version are well documented and equivalent to those of the original version . The Trait part of the State-Trait Anxiety Inventory (STAI-Trait)  was used to assess anxiety as a personality trait. The STAI-Trait is comprised of 20 items rated on a 4-point Likert scale (b1Q=not at all, b4Q=a lot). Participants have to score how they relate to the statements in general. Total score range from 20 to 80, and 59 was used as the cutoff score reflecting clinically significant anxiety. This cutoff score represents two standard deviations (S.D.) above our sample mean. Psychometric properties of the STAI are excellent  as well as the validated French–Canadian adaptation used in the present study . Stress-related measures The Perceived Stress Scale (PSS)  is a 14-item selfreport scale measuring the degree to which situations in one’s life are appraised as stressful. Items represent feelings and thoughts that have occurred in the past month in relation to stressful situations or events. Individuals rate the frequency of each item on a 5-point Likert scale (b0Q=never, b4Q=very often). The higher the total score, the more the person appraises life as unpredictable and uncontrollable. The PSS has adequate test–retest reliability (.85) and internal consistency (.80) and is correlated with a range of self-report and behavioral criteria . A French–Canadian version of the questionnaire was used in the present study. The Coping Inventory for Stressful Situations (CISS)  is a 48-item self-report measure of coping. It is divided into three subscales, each containing 16 items: task-oriented coping, emotion-oriented coping, and avoidance-oriented coping. CISS items illustrate different ways of coping, and respondents are asked to rate on a 5-point scale (b1Q=not at all, b5Q=very much) how each item is representative of their own ways of coping with stress. The higher the score for a scale, the more likely the respondent tends to rely on the type of coping strategies measured by the scale. The CISS has adequate properties with internal alpha reliabilities ranging from .76 (men on the emotion subscale) to .91 (women on the task subscale) [45,46]. A French–Canadian version of the questionnaire was used in the present study. Arousal predisposition The Arousal Predisposition Scale (APS)  is a 12-item inventory that has been designed to measure arousability.
Respondents are asked to report the frequency to which they experience the proposed emotion or behavior on a 5-point Likert scale (b1Q=Never, b5Q=Always). The APS is a useful measure of individual differences in predisposition towards arousability and presents an adequate internal consistency (0.84) . A French–Canadian version of the measure was used. Personality The NEO Five-Factor Inventory (NEO-FFI)  is a 60-item questionnaire measuring five personality domains: neuroticism (N), extraversion (E), openness (O), agreeableness (A), and conscientiousness (C). Each factor is evaluated by 12 items rated on a 5-point Likert scale (strongly disagree to strongly agree). This five-factor model is considered an excellent representation of personality . The psychometric properties of the NEO-FFI in a Canadian context have been considered adequate with internal consistency coefficients of at least .70 for each of the five subscales . A French-Canadian version was used in the present study . Health-related quality of life The SF-12 Health Survey version 2  is a short form of the SF-36, the most widely used health survey. The 12 items are rated on a 5-point Likert scale, and eight subscale scores can be derived from the answers (physical functioning, role physical, bodily pain, general health, vitality, social functioning, role emotional, and mental health). The psychometric properties of the SF-12 version 2 are adequate with reliability coefficients for the eight subscales ranging from 0.73 to 0.87 in general population . A French–Canadian version was used. Data analysis Between-group comparisons (good sleepers, insomnia symptoms, and insomnia syndrome) were performed using chi-squares and analyses of variance (ANOVAs). When significant, Pearson chi-squares were followed by three post hoc comparisons, comparing each group to the others in 22 contingency tables [54–56]. If the post hoc chisquare was higher than the Bonferroni critical value, m2(1, 1 a/c)=m2(1, 1 .05/3)=5.73 , this comparison was considered significant. For significant ANOVAs, multiple comparisons were conducted using the RyanEinot-Gabriel-Welsh F (REGW F) tests to ensure statistically powerful comparisons while controlling alpha error inflation . Then, following Baron and Kenny’s  suggestion, factorial ANOVA (groupsgender) was used to assess the moderating effect of gender on the relationship between sleep status and insomnia correlates (dependent variables). Lastly, a multivariate ordinal (three levels: good sleepers, insomnia symptoms, and insomnia syndrome) logistic regression with cumulative logit link
M. LeBlanc et al. / Journal of Psychosomatic Research 63 (2007) 157 – 166
Table 1 Demographic characteristics of the sample Good sleepers (n=493)
Insomnia symptoms (n=308)
Insomnia syndrome (n=147)
4.7 44.3 21.9 29.1
(23) (219) (108) (144)
4.5 43.1 23.4 29.0
(13) (125) (68) (84)
5.9 50.0 22.4 21.7
(9) (76) (34) (33)
Gender Women Men Marital Status Single/divorced/widowed Married/common-law relationship Education Grade School High School Junior College University Occupation Working/Student Nonworking/retired Family Income V$60 000 z$60 001
SA, strength of association. For ordinal variables, SA was computed as squared Spearman correlation. For continuous variables, SA was computed as Eta squared. SA represents the percentage of variance explained by the sleep quality for each of the dependent variables. Means with different subscripts are significantly different on the REGW multiple comparison test. 4 Pb.05.
function was performed to identify the most important variables in predicting sleep status group membership [59,60]. All predictors were entered in one step into the regression equation. Variance inflation index and collinearity tests were performed to investigate multicollinearity among predictors. Alpha level was set at a two-tailed 5% for all analyses. Most analyses were performed using SPSS (version 10; SPSS, Chicago, IL, USA) except the logistic regression and multicollinearity tests that were completed under SAS System for Windows, Release 9.1 (Cary, NC). Results Participants The overall sample (n=953) included 60% women, and participants’ mean age was 43.7 years (S.D.=14.0; range 18–83). Most participants were Caucasian (98%), had completed at least a high school degree (94.1%), were married or living with a partner (58.3%) and were working (66.2%). Based on the information gathered in the telephone survey, individuals who did not return the questionnaire (n=365) were significantly younger (mean age, 39.9 years; S.D. =15.4) [ F(1,1360)=17.63, Pb.0001] and included a lower proportion of women (51%) than responders [m2(1, n=1362)=7.5, Pb.01]. There were no significant differences between nonresponders and responders regarding marital
status and education, but there was a significant difference regarding sleep satisfaction, with more nonresponders being dissatisfied with their sleep (28.8%) than responders (23.4%) [m2(1, n=1362)=4.2, Pb.05]. Sleep status Five participants could not be classified in one of the three groups because of missing data. Of the 948 remaining participants, 493 (51.7%) were classified as good sleepers, 308 (32.3%) as having insomnia symptoms and 147 (15.4%) as having an insomnia syndrome. Of the last group, 20 individuals did not fulfill all the insomnia diagnostic criteria but used prescribed sleep medication for at least three nights per week. ISI scores were significantly different between groups. Good sleepers obtained lower scores (M=3.7; S.D.=3.2) than the two other groups, and the insomnia symptoms group (M=8.4; S.D.=4.4) presented lower scores than the insomnia syndrome group (M=15.4; S.D.=4.1) [ F(2,945)=573.3, Pb.001]. The same pattern was observed regarding PSQI scores: good sleepers showed lower scores (M=3.6; S.D.=1.8) than the insomnia symptoms group (M=6.1; S.D.=2.7), which presented lower scores than the insomnia syndrome group (M=10.2; S.D.=3.1) [ F(2, 945)=447.9, Pb.001]. Factors associated with insomnia Table 1 presents demographic characteristics of the three sleep status groups. Groups did not significantly differ
M. LeBlanc et al. / Journal of Psychosomatic Research 63 (2007) 157 – 166
Table 2 Sleep, psychological, and health variables (n=948)
Sleep variables Personal history of insomnia (yes) Familial history of insomnia (yes) Psychological variables BDI-II (score z20) STAI-Trait (score z59)
BDI-II STAI-Trait APS PSS CISS Task-oriented coping Emotion-oriented coping Avoidance-oriented coping NEO-FFI Neuroticism Extraversion Openness Agreeableness Conscientiousness Health-related quality of life SF-12 Health Survey General Health Bodily Pain Social functioning Physical functioning Vitality Role physical Role emotional Mental health
Good sleepers (n=493)
Insomnia symptoms (n=308)
Insomnia syndrome (n=147)
5.7a 37.1a 29.9a 21.5a
(5.9) (8.6) (6.8) (6.6)
8.8b 40.0b 31.7b 23.3b
(7.4) (9.0) (6.3) (6.9)
13.9c 46.6c 34.8c 27.5c
(9.0) (9.4) (6.9) (8.2)
80.0944 64.9344 31.1344 42.7344
14.20 12.30 6.10 8.30
55.9 37.8a 45.0a
(9.5) (10.9) (11.0)
55.2 39.8b 43.1b
(9.9) (10.8) (11.3)
54.4 45.4c 44.8a,b
(9.9) (11.5) (10.0)
1.63 27.0944 3.194
0.30 5.40 0.70
15.5a 29.4a 26.4 34.6 36.9
(8.0) (6.3) (5.9) (5.1) (5.8)
17.5b 28.1b 27.3 34.1 36.2
(7.8) (6.5) (6.6) (5.9) (6.3)
22.4c 26.3c 26.1 33.5 36.3
(8.5) (5.9) (6.6) (5.6) (5.7)
42.1744 14.3144 2.59 2.26 1.26
8.30 3.20 0.60 0.50 0.40
75.2a 87.6a 83.1a 85.5a 71.6a 82.8a 81.4a 73.1a
(17.8) (19.7) (19.8) (24.7) (15.2) (19.8) (18.3) (14.8)
71.2b 82.8b 76.5b 81.3b 67.1b 76.6b 74.2b 67.7b
(19.1) (22.7) (21.6) (25.9) (17.8) (22.0) (20.6) (16.3)
61.5c 71.3c 61.6c 67.5c 53.2c 64.3c 61.4c 55.2c
(23.3) (29.5) (24.9) (34.3) (22.0) (25.6) (23.2) (19.1)
29.0844 30.0744 58.5844 24.9644 63.8844 42.9344 59.0044 71.6844
5.80 6.00 11.00 5.00 12.90 8.5 11.0 13.20
For ordinal variables, SA was computed as squared Spearman correlation. For continuous variables, SA was computed as Eta squared. SA represents the percentage of variance explained by the sleep status group membership for each of the dependent variables. Means with different subscripts are significantly different on the REGW multiple comparison test. 4 Pb.05. 44 Pb.01.
regarding marital status and education. In contrast, there were significant differences between groups regarding age [ F(2,938)=4.0, Pb.05], gender [m2(2, n=946)=7.09, Pb.05], occupation m2 (2, n=937)=8.96, Pb.05], and family income [m2(2, n=888)=8.64, Pb.05]. Post hoc comparisons revealed that the good sleepers group was significantly younger compared to the insomnia syndrome group but not compared to the insomnia symptoms group, which, in turn, did not significantly differ from the insomnia syndrome group. The proportion of women was higher in the insomnia syndrome group relative to the insomnia symptoms and the good sleepers groups. Regarding occupation, the proportion of individuals working or studying was higher in the good sleepers group compared to the insomnia symptoms and syndrome groups. Lastly, the proportion of individuals with higher incomes was higher in the good sleepers group compared to the insomnia syndrome group but not relative to the insomnia symptoms group.
Table 2 presents data for insomnia history (personal and familial), psychological variables, and health-related quality of life. There were significantly more individuals reporting a previous episode of insomnia in the insomnia syndrome group than in the two other groups and in the insomnia symptoms group compared to good sleepers. There was no significant between-group difference for family history of insomnia, although good sleepers presented a lower proportion than the other groups. For psychological measures, both the BDI-II and the STAI-Trait mean scores were significantly different among the three groups. When BDI-II scores were computed without the item assessing sleep disturbances, group means were still significantly different (5.3 for good sleepers, 7.9 for insomnia symptoms and 12.5 for insomnia syndrome) [ F(2,938)=70.15, Pb.01]. The proportion of individuals presenting a score z20 was significantly different between groups, as was the proportion of individuals presenting a STAI-Trait score z59. The were
M. LeBlanc et al. / Journal of Psychosomatic Research 63 (2007) 157 – 166 Table 3 Three-category (good sleepers, insomnia symptoms, and insomnia syndrome) ordinal logistic regression results (n=931) Analysis of estimates
Predictors Previous episode of insomnia BDI-II STAI-Trait PSS CISS Emotion-oriented coping APS NEO-FFI Neuroticism Extraversion SF-12 health survey General health Bodily pain Social functioning Physical functioning Vitality Role physical Role emotional Mental health
Odds ratio point estimatea
95% Wald confidence limits
1.05 0.99 1.00
1.02 0.96 0.97
1.08 1.03 1.03
11.12 0.12 0.05
b.01 .73 .81
1.00 0.99 1.00 1.00 0.99 0.99 0.99 0.99
0.99 0.99 0.99 0.99 0.98 0.98 0.99 0.98
1.01 1.00 1.01 1.00 1.00 1.00 1.00 1.00
0.00 0.49 0.42 0.34 5.37 2.87 1.77 2.29
.97 .48 .52 .56 .02 .09 .18 .13
observations (listwise, missing n=22 cases or 2.3%) were submitted to the analysis (483 good sleepers, 302 individuals with insomnia symptoms, and 146 individuals with an insomnia syndrome). Since two predictors exhibited high variance inflation values (STAI-Trait=5.8; NEO-FFI neuroticism subscale=3.6) but no problems were noted on other multicollinearity tests, no predictors were removed from the logistic regression. The final model exhibited a moderate fit between observed and predicted group membership (pseudo-R 2=.25, 57.0% of correct classification). Three variables [i.e., previous episode of insomnia, BDI-II [odds ratio (OR)=1.05], and SF-12 vitality subscale (OR=0.99)] were significantly associated with the presence of an insomnia syndrome, whereas one other SF-12 subscale (role physical, OR=0.99) was near statistical significance (see Table 3). Thus, individuals who previously experienced insomnia were 2.55 (OR=2.55) times more at risk of being classified in a more severe category of insomnia than those who never experienced insomnia in the past. Moreover, each increase of one point on the BDI-II is associated with a 5% increase (OR=1.05), and each increase of one point of the SF-12 vitality subscale is associated with a 1% decrease (OR=0.99) of the risk of being in a more severe category (i.e., insomnia symptoms or syndrome).
This odds ratio is estimated by exponentiating the corresponding parameter estimate of h, B.
Discussion also significant differences on the PSS, the CISS emotionoriented coping subscale, the APS, and the NEO-FFI neuroticism and extraversion subscales, with the insomnia syndrome group presenting higher scores than the two other groups and the insomnia symptoms group presenting higher scores than good sleepers. Scores on the CISS avoidanceoriented coping subscale were significantly higher for the good sleepers group compared to the insomnia symptoms group but not compared to the insomnia syndrome group. For health-related quality of life, all SF-12 subscales were significantly different across groups. The insomnia syndrome group showed scores suggesting a poorer quality of life than the two other groups, and the insomnia symptoms group showed scores suggesting a poorer quality of life than good sleepers. Factorial ANOVAs (groupgender) were conducted to control for the effect of a higher proportion of women than men in the sample. Results showed that gender did not have a moderating effect on the relationship between sleep status and any of the psychological and health-related quality of life variables. A multivariate ordinal (three levels) logistic regression was performed to identify the most important variables in predicting sleep status membership. Variables entered in the equation included previous episode of insomnia (yes/no), BDI-II, STAI-Trait, APS, PSS, the CISS emotion-oriented coping subscale, the NEO-FFI neuroticism and extraversion subscales, and the eight SF-12 subscales. A total of 931
The present study reveals that almost all factors traditionally associated with insomnia in studies conducted with selected clinical samples also emerge as insomnia correlates in a population-based sample. Results suggest that individuals with insomnia endorse more psychological symptomatology and more impairments of quality of life than good sleepers, with degree of impairment increasing linearly with insomnia severity. Results of this study highlight the critical role of mental health in insomnia. Indeed, several mental health-related variables (e.g., BDI-II, and SF-12 mental health) differed significantly across groups, with depressive symptomatology among the most reliable predictors of sleep status group membership. Moreover, a considerable number of individuals in the insomnia symptoms and syndrome groups (11.5% and 26.8%, respectively) obtained BDI-II scores z20, indicating depressive symptoms of at least moderate intensity , compared to only 4.2% of good sleepers exceeding that threshold. Several epidemiological studies have already shown that individuals with insomnia complaints present higher levels of depression and anxiety symptoms than those without insomnia [6,10–12,61]. In the present study, the distinction between insomnia symptoms and syndrome showed that even when sleep difficulties are less severe, anxiety, neuroticism and depressive symptomatology are more salient than in good sleepers. However, given that all these measures are highly correlated, it is unclear whether this is reflecting different
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psychological dimensions of insomnia or a more generic psychological distress profile. Furthermore, those results are similar to some previous studies that suggested that the presence of neurotic symptoms, emotional inhibition and an inability to discharge anger characterizes individuals with insomnia [16–18,20,22]. Our study was innovative in its use of the NEO-FFI, which provided an overview of emotional, attitudinal, and motivational styles, rather than simply an assessment of symptoms of mental health disorder. Individuals with insomnia (i.e., symptoms or syndrome) reported higher arousal predisposition than good sleepers, suggesting that they were more psychologically aroused, not only at bedtime but as a general trait feature. Those with insomnia symptoms and syndrome also reported higher scores on the PSS and on the CISS emotion-coping subscale than good sleepers. These findings are consistent with our previous study , which also showed that individuals with insomnia presented higher levels of bedtime arousal, perceived their lives as more stressful and relied more on emotion-focused coping strategies than good sleepers. Collectively, these findings support the model suggesting that the relationship between daytime stress and nighttime sleep is mediated by bedtime arousal . Nonetheless, it is only through prospective longitudinal studies that the hypothesis that increased arousal is a predisposing factor for insomnia development may be confirmed. Lastly, we found that a previous episode of insomnia was among the best predictors of sleep status group membership, a finding also reported by Klink et al. . The rate of prior history of insomnia among the insomnia syndrome (51%) was similar to those observed in previous studies (44% ; 56% ). Thus, these results would indicate that insomnia is a recurrent problem for most people. Unlike previous studies [31,32] however, there was no relation between family history of insomnia and presence of insomnia symptoms and syndrome. This research has some limitations, including its crosssectional nature, which precludes any definite conclusions about the direction of the relation between insomnia and its correlates. Do psychological factors and health-related quality of life play a role in the development of sleep difficulties as predisposing factors, precipitating factors or consequences? Personal and family history of insomnia, arousal predisposition, and personality traits are generally conceptualized as predisposing factors to insomnia, whereas health-related quality of life is usually considered as a consequence of insomnia. However, further longitudinal studies are needed to corroborate those hypotheses. The lack of differentiation between primary insomnia and insomnia secondary to a mental, medical, or other sleep disorder also warrants a cautious interpretation of the results. Significant physical and mental health problems are frequently associated with insomnia and may have been confounding factors in the observed associations between sleep status and the variables measured. Insomnia could be
the consequence or a symptom of another difficulty, such as depression or a chronic disease, and the fact that we did not document the presence of physical and mental health disorders with standardized diagnostic procedures restricts the interpretation of our results. For example, the finding that bodily pain and physical conditions are important variables in predicting group membership could be explained by secondary insomnia, or on the other hand, those two variables could simply reflect insomnia consequences. Also, new independent variables like genetic, cultural, environmental, lifestyle, and health-related variables (e.g., medical disorders, medication utilization) should be further explored as potential insomnia correlates. Finally, although the current sample was population-based, the proportion of women and individuals dissatisfied with their sleep was higher than in the general population, limiting the generalization of the results. Despite these limitations, this study sheds new light on the topic of insomnia correlates. Firstly, with a populationbased sample that included both good sleepers and individuals with different degree of insomnia severity, this study may have captured a more accurate representation of the association between sleep quality and psychological and health-related quality of life correlates. The inclusion of individuals with insomnia symptoms suggested that sleep quality may be best illustrated by a continuum rather than dichotomously and that insomnia correlates (e.g., depressive symptoms and anxiety) may also follow the same pattern. Psychological distress and quality-of-life impairment increased with insomnia severity. Those results could also guide the development of effective early intervention programs to prevent chronic insomnia or the development of other mental health disorders (e.g., major depression) as soon as the first insomnia symptoms are noticed. Secondly, this study focuses attention on the importance of rigorous definition of insomnia with the utilization of a welloperationalized algorithm, based on insomnia diagnostic criteria from DSM-IV-TR  and ICD-10 , to determine the quality of participants’ sleep. Moreover, significant between-group differences, both on the PSQI and the ISI, support our sleep status classification algorithm, with scores obtained on these two measures following a linear gradation of sleep difficulties. Longitudinal research is needed to assess the relative contribution of those factors in the first onset and evolution of insomnia over time. With repeated follow-up assessments, we may also be able to identify risk factors for insomnia and predictors or moderating variables of insomnia remission and relapse.
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