Repeated measures regression mixture models.

Regression mixture models are one increasingly utilized approach for developing theories about and exploring the heterogeneity of effects. In this study we aimed to extend the current use of regression mixtures to a repeated regression mixture method when repeated measures, such as diary-type and experience-sampling method, data are available. We hypothesized that additional information borrowed from the repeated measures would improve the model performance, in terms of class enumeration and accuracy of the parameter estimates. We specifically compared three types of model specifications in regression mixtures: (a) traditional single-outcome model; (b) repeated measures models with three, five, and seven measures; and (c) a single-outcome model with the average of seven repeated measures. The results showed that the repeated measures regression mixture models substantially outperformed the traditional and average single-outcome models in class enumeration, with less bias in the parameter estimates. For sample size, whereas prior recommendations have suggested that regression mixtures require samples of well over 1,000 participants, even for classes at a large distance from each other (classes with regression weights of .20 vs. .70), the present repeated measures regression mixture models allow for samples as low as 200 participants with an increased number (i.e., seven) of repeated measures. We also demonstrate an application of the proposed repeated measures approach using data from the Sleep Research Project. Implications and limitations of the study are discussed.

Health and demographic discriminators of an insomnia identity and self-reported poor quantitative sleep.

OBJECTIVES: To identify factors that most saliently characterize the profile of individuals who complain of chronic insomnia, with or without quantitative sleep impairment. DESIGN: Community-dwelling adults reported on their demographics and functioning via questionnaires and completed 2 weeks of sleep diaries. SETTING: Shelby County in the Memphis, TN, area. PARTICIPANTS: Population-based sample, stratified by sex and age to maximally represent sleep and health across the life span. MEASUREMENTS: Participants were classified into 4 groups according to whether or not they endorsed a chronic insomnia complaint and whether they demonstrated good or poor quantitative sleep on diaries. Discriminant analysis determined which of the following variables significantly maximized spread among the sleep groups: age, sex, race, body mass index, household education, number of medications, frequency of substance use, number of medical conditions, depression, anxiety, fatigue, daytime sleepiness, and daytime insomnia impact. RESULTS: On the most powerful discriminant function, participants with more medical conditions, greater depression and anxiety, and older age were more likely to complain of chronic insomnia than to not complain and, within these levels, to have poor rather than good quantitative sleep. A second function found African Americans particularly likely to be noncomplaining poor sleepers compared to Whites. CONCLUSIONS: Findings make progress in clarifying the profile of individuals who self-identify as having chronically poor sleep. Notably, general depression and anxiety surpassed sleep-related daytime impairment measures in discriminating complaining sleepers. Negativistic self-appraisals driving diffuse psychological symptoms may thus be viable intervention targets for reducing persistent insomnia complaints independently of sleep-specific concerns.

Intraindividual sleep variability and its association with insomnia identity and poor sleep.

OBJECTIVE: Insomnia identity refers to the conviction that one has insomnia, which can occur independently of poor sleep. Night-to-night variability in sleep (termed intraindividual variability [IIV]) may contribute to insomnia identity yet remain undetected via conventional mean analyses. This study compared sleep IIV across four subgroups: noncomplaining good sleepers (NG), complaining poor sleepers (CP), complaining good sleepers (CG), and noncomplaining poor sleepers (NP). METHODS: This study analyzed 14 days of sleep diary data from 723 adults. Participants were classified according to presence/absence of a sleep complaint and presence/absence of poor sleep. A 2 × 2 multivariate analysis of covariance (MANCOVA) was performed to explore differences on five measures of sleep IIV: intraindividual standard deviation in total sleep time (iSD TST), sleep onset latency (iSD SOL), wake after sleep onset (iSD WASO), number of nightly awakenings (iSD NWAK), and sleep efficiency (iSD SE). RESULTS: MANCOVA revealed significant main effects of poor sleep, sleep complaint, and their interaction on sleep IIV. Poor sleepers exhibited greater IIV across all sleep parameters compared to good sleepers. Similarly, individuals with a sleep complaint exhibited greater IIV compared to individuals with no complaint. The interaction revealed that iSD SOL was significantly greater among CP than NP, and iSD NWAK was significantly greater among CG than NG. CONCLUSIONS: Greater night-to-night variability in specific sleep parameters was present among complaining versus noncomplaining sleepers in good and poor sleep subgroups. These findings suggest certain aspects of sleep consistency may be salient for treatment-seeking individuals based on their quantitative sleep status.

Insomnia Complaint Versus Sleep Diary Parameters: Predictions of Suicidal Ideation.

The purpose of this study was to determine which aspects of insomnia best predict suicidal ideation (SI). Participants were grouped according to whether they complained of insomnia and whether their sleep would be characterized as poor or good by applying quantitative criteria for insomnia to their sleep diary data. Analyses revealed that insomnia complaint was more strongly associated with SI than was poor sleep. These findings suggest that patients who complain of insomnia, regardless of the presence or absence of poor sleep, may be at greater risk for suicide than those who are content with their sleep.

Variability in self-reported normal sleep across the adult age span.

OBJECTIVES: Illustrate the importance of examining within- and between-person differences in sleep across the adult age span. METHOD: Two weeks of sleep diary data were analyzed for 592 normal sleepers ranging in age from 20 to 96 years. Variability in total sleep time (TST), number of nighttime awakenings (NWAK), sleep-onset latency (SOL), and wake-time after sleep onset (WASO) were examined overall and by age, sex, and race utilizing multilevel models and multiple regression. RESULTS: Night-to-night differences in sleep within the same individual generally exceeded differences between individuals for TST, SOL, and WASO. The amount of intraindividual variability in TST and NWAK decreased with older age. Further, the degree of reduction in variability in TST associated with age depended on sex and race, with young black females showing the greatest variability. In general, females tended to have more intraindividual variability in SOL and NWAK than males, while race differences were complicated by high variability between blacks. DISCUSSION: To truly assess and understand individual differences in the sleep of older adults, future research needs to take into account night-to-night variability (including what makes sleep vary from one night to the next), in addition to average sleep.

Hopelessness mediates the relation between insomnia and suicidal ideation.

INTRODUCTION: A growing body of literature indicates that insomnia is related to suicidality. However, the mechanism through which insomnia correlates with suicide risk is unclear. The goal of the present research was to determine whether hopelessness, a robust predictor of suicidality, mediates the relation between insomnia and suicidal ideation (SI). METHODS: The present study used archival data from community-dwelling adults. Participants (n = 766) completed a Health Survey, two weeks of daily sleep diaries, and five measures of daytime functioning, including the Beck Depression Inventory (BDI). BDI item 2 was used to assess hopelessness, and BDI item 9 was used to assess SI. Criteria from the DSM-5 as well as quantitative criteria were used to identify participants with insomnia (n = 135). RESULTS: The analyses revealed that hopelessness is a significant mediator of the relation between insomnia and SI. After adding depression as an additional mediator, hopelessness remained a significant predictor of SI. CONCLUSION: The present research suggests the need for clinicians to routinely screen clients who have insomnia for hopelessness and SI, and to treat hopelessness when it is present. Further research should address the limitations in this sample and should also consider other potential mediators of the insomnia-SI link.

Epidemiology of bedtime, arising time, and time in bed: analysis of age, gender, and ethnicity.

This study investigated the epidemiology of bedtime (BT), arising time (AT), and time in bed (TIB) as a function of age, gender, and ethnicity. Sleep diary data were analyzed for 746 randomly selected community participants. This sample was comprised of 364 men (48.8%) and 382 women (51.2%), 532 Caucasians (71.3%) and 214 African Americans (28.7%), and participant ages ranged from 20 to 98 years. Regression analyses showed a main effect of age on subjective BT, AT, and TIB. The addition of gender and ethnicity to the regression model added significant variance for TIB, but not BT or AT. In general, BT declined across the lifespan, but AT showed a quadratic pattern that peaked in young adulthood, was stable in the middle years, and peaked again in the later years. This age-related combination of BT and AT resulted in greater TIB for older adults than other age groups. Women spent significantly greater TIB than men, and African Americans spent significantly more TIB than Caucasians. These results suggest that there are distinct behavioral sleep patterns associated with age and, in the case of TIB, gender and ethnicity. These patterns may have significant clinical implications, particularly with respect to age.

Predictors of perceived sleep quality among men and women with insomnia.

The present study determined which self-reported sleep variables and daytime impairment measures are most closely associated with sleep quality ratings (SQR) in men and women with insomnia. The participants were 137 people with insomnia, 56 men and 81 women. Multiple regression found that for men, sleep efficiency best predicted SQR, explaining 26.9% of variance. A similar analysis was conducted for women. After race was entered as a covariate, number of awakenings and total sleep time were significant predictors of SQR. Collectively, race, number of awakenings, and total sleep time explained 35.7% of variance. This suggests that the middle-of-the-night experience predicts sleep quality rating in women with insomnia, whereas the full night experience predicts sleep quality ratings in men with insomnia.

Association between report of insomnia and daytime functioning.

OBJECTIVES: The relationship between reports of insomnia and daytime functioning was investigated using hierarchical regression. The presence or absence of a report of insomnia was the predictor of primary interest. A number of covariates were included in the model: demographic variables, health variables, and quantitative sleep parameters. METHODS: Data were collected from a community sample in the Memphis, Tennessee area. Data from 734 volunteers, ranging in age from 20 to 96years were analyzed. The sample included 235 individuals who reported having chronic insomnia and 499 individuals who reported no sleep problems. Participants completed a 2-week sleep diary, a battery of daytime functioning questionnaires, and a medical disorders checklist. Demographic information was also collected. The daytime functioning assessment included the Beck Depression Inventory, the State-Trait Anxiety Inventory, the Epworth Sleepiness Scale, the Insomnia Impact Scale, and the Fatigue Severity Scale. The hierarchical regression model included four sets. The first three sets consisted of 18 variables capturing demographic, health, and sleep diary parameters. The fourth set included a single dichotomous variable representing the presence or absence of a report of insomnia. RESULTS: Reports of insomnia were a significant predictor of all five daytime functioning measures, which is consistent with previous research. We also showed that reports of insomnia were able to uniquely explain a significant amount of variability in self-reported daytime functioning after controlling for demographics, health, and sleep diary variables. The pattern of individual variables that reached significance in the first three sets varied depending on which daytime functioning measure was predicted, however, age, the presence of pain, the presence of mental health problems, SOL, and WASO were the most commonly significant predictors of poor daytime functioning from these sets across measures. CONCLUSIONS: Individuals' perceptions of their sleep are related to differences in their reported daytime functioning, which are not accounted for by demographic factors, health surveys, or quantitative sleep assessments. Reports of insomnia may be related to a set of common cognitive factors among individuals who report having insomnia which cause them to be distressed with their sleep and increase their dissatisfaction with daytime functioning. Relevance of the findings to insomnia research and clinical management are discussed.

Self-reported sleep, demographics, health, and daytime functioning in young old and old old community-dwelling seniors.

Sleep, demographics, health, and daytime functioning were examined in young old (60-74 years; n = 175) and old old (75-98 years; n = 147) community-dwelling seniors. Sleep diaries (2 weeks), 6 daytime functioning measures, and a demographics-health questionnaire were collected. The old old reported worse sleep than the young old. Women reported worse sleep than men. Hierarchical regressions revealed demographic information alone was not sufficient for understanding sleep. Specifically, demographic information predicted sleep onset latency and sleep efficiency for both groups, but not number of awakenings or total nap time. Health and daytime functioning accounted for significant increases in the variance in sleep "over and above" that accounted for by demographics alone or demographics and health combined, respectively. All variables combined accounted for 15% to 30% of the variance in sleep. Because the importance of specific measures varied by group and sleep variable, research exploring the differential utility of specific measures for young old versus old old appears warranted.

Vitamins and sleep: an exploratory study.

STUDY OBJECTIVE: We analyzed archival data from an epidemiology study to test the association between vitamin use and sleep. DESIGN: Random digit dialing was used to recruit 772 people ranging in age from 20 to 98 for a study of people's sleep experience. These individuals completed a set of questionnaires about their sleep, health, and daytime functioning. Five hundred and nineteen of these participants had available vitamin use data. SETTING: Home. PARTICIPANTS: Five hundred and nineteen people participated. Recruitment applied minimal screening criteria and no attempt was made to favor people with or without sleep disturbance. INTERVENTIONS: This survey included no intervention. Participants completed 2 weeks of sleep diaries and a set of questionnaires. Of particular salience to the present study, participants reported their vitamin use in listing all medications and nutritional supplements being used currently. MEASUREMENTS AND RESULTS: For those individuals taking a multivitamin or multiple single vitamins, sleep diaries revealed poorer sleep compared to non-vitamin users in the number and duration of awakenings during the night. After controlling for age, ethnicity, and sex the difference in number of awakenings was still marginally significant. The rate of insomnia, conservatively defined, and consumption of sleep medication were also marginally significantly higher among individuals taking multi-/multiple vitamins compared to those not taking vitamins. CONCLUSIONS: Disturbed sleep maintenance was associated with multi-/multiple vitamin use. Five equally plausible explanations were advanced to explain this association including vitamins cause poor sleep, poor sleepers seek vitamins, and unidentified factors promote both poor sleep and vitamin use. These data are considered preliminary. Methodological characteristics of future studies were described that hold the promise of more clearly illuminating the association between vitamins and sleep.

Comorbidity of chronic insomnia with medical problems.

STUDY OBJECTIVES: Determine the comorbidity of insomnia with medical problems. DESIGN: Cross-sectional and retrospective. PARTICIPANTS: Community-based population of 772 men and women, aged 20 to 98 years old. MEASUREMENTS: Self-report measures of sleep, health, depression, and anxiety. RESULTS: People with chronic insomnia reported more of the following than did people without insomnia: heart disease (21.9% vs 9.5%), high blood pressure (43.1% vs 18.7%), neurologic disease (7.3% vs 1.2%), breathing problems (24.8% vs 5.7%), urinary problems (19.7% vs 9.5%), chronic pain (50.4% vs 18.2%), and gastrointestinal problems (33.6% vs 9.2%). Conversely, people with the following medical problems reported more chronic insomnia than did those without those medical problems: heart disease (44.1% vs 22.8%), cancer (41.4% vs 24.6%), high blood pressure (44.0% vs 19.3%), neurologic disease (66.7% vs 24.3%), breathing problems (59.6% vs 21.4%), urinary problems (41.5% vs 23.3%), chronic pain (48.6% vs 17.2%), and gastrointestinal problems (55.4% vs 20.0%). When all medical problems were considered together, only patients with high blood pressure, breathing problems, urinary problems, chronic pain, and gastrointestinal problems continued to have statistically higher levels of insomnia than those without these medical disorders. CONCLUSION: This study demonstrates significant overlap between insomnia and multiple medical problems. Some research has shown it is possible to treat insomnia that is comorbid with select psychiatric (depression) and medical (eg, pain and cancer) disorders, which in turn increases the quality of life and functioning of these patients. The efficacy of treating insomnia in many of the above comorbid disorders has not been tested, indicating a need for future treatment research.

The influence of age, gender, ethnicity, and insomnia on Epworth sleepiness scores: a normative US population.

BACKGROUND AND PURPOSE: This study explored the distribution of Epworth Sleepiness Scale (ESS) scores in a randomly sampled, community population and provided percentile scores that will assist in decision-making in both research and clinical settings. PATIENTS AND METHODS: Participants included 703 individuals between the ages of 20 and 98, with 116 people with insomnia (PWI) and 587 people not having insomnia (PNI). Analyses produced main effects for sleep status and ethnicity. RESULTS: PWI had higher ESS scores than PNI and African-Americans had higher ESS scores than Caucasians, although effect sizes were small. Gender, age group, and season did not impact ESS scores. Receiver operating characteristic (ROC) curve analysis proved the ESS to discriminate poorly between PWI and PNI. CONCLUSIONS: This study found higher percentages of 'sleepy' individuals than previous studies. PWI did have slightly elevated scores on the ESS, but this elevation was not necessarily predictive of an insomnia diagnosis. Results support a continuum of sleepiness/alertness among PWI.

Sleep hygiene practices in two community dwelling samples of older adults.

STUDY OBJECTIVES: Common sleep hygiene practices were examined in 2 community-based samples of older adults to determine which practices differentiated 4 sleep subgroups: noncomplainers without insomnia symptoms, complainers without insomnia symptoms, noncomplainers with insomnia symptoms, and complainers with insomnia symptoms. DESIGN: Two weeks of sleep diaries provided napping and bed/out-of-bed time variability data. A retrospective questionnaire provided data on caffeine, cigarette, and alcohol usage. Recruitment involved random digit dialing (Sample 1) and advertisements (Sample 2). SETTING: Memphis, TN area (Sample 1); Gainesville, FL area (Sample 2). PARTICIPANTS: 310 individuals 60-96 years (Sample 1); 103 individuals 60-89 years (Sample 2). INVENTIONS: N/A. MEASUREMENTS AND RESULTS: Older individuals with sleep complaints did not report engaging in poorer sleep hygiene practices than those without complaints with the exception of frequency of napping. For Sample 1 only, complainers reported napping on 1.5-2.0 more days per week than noncomplainers. Sleep subgroups in both samples did not differ for the other sleep hygiene practices studied. CONCLUSIONS: Overall, sleep hygiene behaviors did not differentiate the 4 sleep subgroups. The efficacy of sleep hygiene as a therapy for late life insomnia appears questionable in this context. Both complaining sleep subgroups napped more frequently than both noncomplaining subgroups in Sample 1. Additional research is needed to clarify the clinical implications of nap frequency as these results did not replicate in Sample 2, and the impact of napping on nighttime sleep remains unclear. Inconsistencies with previous research in younger samples support the need for more research specifically targeting older individuals' sleep patterns and behaviors.

Socioeconomic status and insomnia.

This investigation compared the likelihood of insomnia and insomnia-related health consequences among individuals of different socioeconomic status. A random-digit dialing procedure was used to recruit at least 50 men and 50 women in each age decade from 20 to 80+ years old. Participants completed 2 weeks of sleep diaries as well as questionnaires related to fatigue, sleepiness, and psychological distress. Socioeconomic status was measured by education status assessed at 3 different levels: individual, household, and community. Results indicated that individuals of lower individual and household education were significantly more likely to experience insomnia even after researchers accounted for ethnicity, gender, and age. Additionally, individuals with fewer years of education, particularly those who had dropped out of high school, experienced greater subjective impairment because of their insomnia.

The relation between smoking and sleep: the influence of smoking level, health, and psychological variables.

The relation between smoking and sleep was examined in a randomly selected sample of 769 individuals (379 men and 390 women, ages 20 to 98). Participants completed 2 weeks of sleep diaries, provided a global report on their sleep, indicated the number of cigarettes smoked per day, and supplied information on health, depressive symptoms, anxiety, and caffeine and alcohol use. After controlling for demographic, health, psychological, and behavioral variables, light smoking (< 15 cigarettes per day), but not heavier smoking, was associated with self-reported chronic insomnia and reduced sleep diary total sleep time and time in bed. Smokers did not differ significantly from nonsmokers on diary measures of sleep-onset latency, number of awakenings during the night, wake time after sleep onset, or sleep efficiency.

The reliability and predictive value of adolescents' reports of initial reactions to smoking.

A sample of 372 adolescents completed annual surveys regarding their initial reactions to smoking (IRTS) and their current smoking status. Each annual survey asked participants if they had the following five reactions the first time they smoked a cigarette: coughing, or feeling dizzy, sick, high, or relaxed. Time 1 IRTS data were collected within 1 year of the reported initial smoking experience, and Time 2 IRTS data were collected 1 year later. Kappa values for two IRTS items, coughing (.45) and dizziness (.40), indicated modest but acceptable reliability across a 1-year period, but the remaining items showed poor reliability (all < or =.31). Logistic regression analyses indicated that no IRTS item significantly predicted regular (at least weekly) smoking 1 year later. However, when IRTS and smoking status were assessed concurrently (at Time 2), reports of feeling relaxed and not coughing during the initial episode were significantly correlated with regular smoking. Participants who progressed from experimental to regular smoking from Time 1 to Time 2 were more likely to report relaxation as an initial reaction to smoking at Time 2 after denying relaxation at Time 1.

Ethnic differences in smoking withdrawal effects among adolescents.

Smoking withdrawal effect information was collected from 75 adolescents (54 males and 21 females) making a quit attempt during a school-based smoking cessation program. A strong need to smoke was the most common withdrawal effect (60%), followed by irritability (51%), and difficulty concentrating (41%). Most (61%) participants experienced two or more withdrawal effects during the quit attempt, and withdrawal effects were evident in those smoking less than daily. Significant ethnic differences were found, with African Americans reporting significantly fewer withdrawal effects than Caucasians. After controlling for smoking frequency, African Americans were still less likely to report irritability, difficulty concentrating, and restlessness. Participants who chose to use nicotine replacement during the quit attempt were more likely to report difficulty concentrating, restlessness, and feeling miserable.

'Young old' and 'old old' poor sleepers with and without insomnia complaints.

OBJECTIVE: Sleep, psychological adjustment, health and insomnia complaints were examined in 277 community-dwelling seniors in order to identify characteristics that distinguish poor sleepers with complaints (likely to seek treatment) and those without complaints (unlikely to seek treatment). METHODS: Two weeks of sleep diaries and other sleep-related measures were collected. Young old (65-74 years) and old old (75+) participants were categorized as: good sleepers, poor sleepers with complaints (complainers), and poor sleepers without complaints (noncomplainers). RESULTS: In both age groups, complainers had poorer sleep than noncomplainers. Complainers also reported more depressive symptoms and had poorer health than noncomplainers. The old old slept longer each night, but took longer to fall asleep, napped more, and were more likely to complain of insomnia than the young old; otherwise, the young old/old old distinction did not explain sleep differences among the three types of sleepers. CONCLUSIONS: Implications for treating late-life insomnia include greater inclusion of the old old in treatment outcome research and more focus on the development of integrated intervention and prevention strategies that target health, depressive symptoms, and sleep.

Characteristics of adolescents caught with cigarettes at school: implications for developing smoking cessation programs.

A potential method of recruiting adolescents for smoking cessation interventions is to offer treatment to students who have been caught with cigarettes at school. The present investigation surveyed 110 adolescents after they were caught with cigarettes at school. The majority of participants were daily smokers (65%) and 17% of the sample scored > or =6 on a version of the Fagerström Tolerance Questionnaire. Smoking was pervasive in their social environment, with approximately half the sample reporting that all five of their five best friends smoked. Interest in quitting was evident. Most had made a quit attempt during the past year (71%) and two-thirds planned to quit within the next 6 months. However, questionable strategies (e.g., increasing caffeine consumption) had been used during previous quit attempts. The implications for developing school-based smoking cessation programs are discussed.