Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “linear mixed model”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78Linked to original sources
PubMed2002

Impact of body mass index on changes in common carotid artery wall thickness.

OBJECTIVE: To examine associations between changes in body mass index (BMI) and changes in carotid artery intima-media thickness (IMT) in a community-based sample. RESEARCH METHODS AND PROCEDURES: Carotid artery IMT and BMI were assessed at baseline (between 1987 and 1990) and in three subsequent examinations at 3-year intervals in participants in the Atherosclerosis Risk in Communities cohort. The 9,316 African-American and white men and women in the analysis were 45 to 64 years of age at baseline. Cross-sectional associations between BMI and IMT were assessed using general linear models. Longitudinal associations were examined using mixed models analysis. RESULTS: Cross-sectional associations between BMI and IMT were confirmed. At baseline, a 1-kg/m(2) increase in BMI was associated with an increase in IMT that ranged from 2.5 to 7.5 micro m among the ethnic-gender groups examined. Changes in BMI were not associated with changes in IMT in models that adjusted for aging and other covariates. Results were similar across ethnic-gender groups. DISCUSSION: Among free-living, 45- to 64-year-old adults, changes in common carotid artery IMT associated with changes in BMI are either very small or absent.

Aged↗
PubMed2005

Prediction of lower permanent canine and premolars width by correlation methods.

The aim of this study was to determine linear regression equations to estimate the widths of unerupted lower permanent canines and premolars using measurements obtained from 45 degrees oblique teleradiographs. The sample consisted of 30 white Caucasian patients orthodontically treated at the Faculty of Dentistry, Universidade Federal do Rio de Janeiro. The records for each patient included a 45 degrees oblique teleradiograph (left side) in the mixed dentition period and a dental cast of the permanent dentition. Pearson's test was applied between each lower canine, first and second premolars measured on the radiograph, and the sum of their actual widths measured on the dental cast. The strongest correlation occurred for the first premolars for one side (.82) and both sides (.84). One linear regression equation was determined to estimate the widths of un-erupted lower canine and premolars of both sides from a single measurement of the first premolar.

Bicuspid↗
PubMed2006

Profile likelihood-based confidence intervals using Monte Carlo integration for population pharmacokinetic parameters.

Population pharmacokinetic (PPK) analysis usually employs nonlinear mixed effects models using first-order linearization methods. It is well known that linearization methods do not always perform well in actual situations. To avoid linearization, the Monte Carlo integration method has been proposed. Moreover, we generally utilize asymptotic confidence intervals for PPK parameters based on Fisher information. It is known that likelihood-based confidence intervals are more accurate than those from the usual asymptotic confidence intervals. We propose profile likelihood-based confidence intervals using Monte Carlo integration. We have evaluated the performance of the proposed method through a simulation study, and analyzed the erythropoietin concentration data set by the method.

Computer Simulation↗
PubMed2003

Effect of fluoroquinolone expenditures on susceptibility of Pseudomonas aeruginosa to ciprofloxacin in U.S. hospitals.

The effect of fluoroquinolone use on the susceptibility of Pseudomonas aeruginosa to fluoroquinolones in U.S. hospitals was studied. Benchmarking surveys were sent annually to pharmacists practicing in U.S. hospitals from 1993 to 1999. Data collected included hospital characteristics, antimicrobial expenditures and use, antimicrobial stewardship activities, and bacterial susceptibilities. Antimicrobial expenditures were normalized for the number of occupied beds (OBs) per year. General linear modeling and repeated-measures mixed-effects modeling were used to determine factors predictive of P. aeruginosa susceptibility to fluoroquinolones. A total of 174 hospitals provided data for fluoroquinolone expenditures and susceptibility of P. aeruginosa; the median number of years of data was 3 (range, 1-6), representing 416 hospital years. Community hospitals contributed a majority of the data. Median fluoroquinolone expenditures increased gradually from $230 per OB in 1993 to $400 per OB in 1998. A 55% increase to $620 per OB occurred in 1999, largely because of increased spending on levofloxacin. Susceptibility to ciprofloxacin was commonly used to assess fluoroquinolone susceptibility. The median susceptibility of P. aeruginosa to ciprofloxacin decreased from 84% to 71%. Increasing expenditures for ofloxacin and levofloxacin, but not ciprofloxacin, were associated with decreasing P. aeruginosa susceptibility to ciprofloxacin. In the final multivariable model, each study year after 1993 and every increase in ofloxacin expenditure of $100 per OB were associated with decreases in P. aeruginosa susceptibility. Data from a benchmarking survey of U.S. hospitals for 1993-1999 revealed increases in levofloxacin expenditures, total fluoroquinolone expenditures, expenditures for nonfluoroquinolone antipseudomonal antimicrobials, and total antimicrobial expenditures in 1999. Increases in expenditures for levofloxacin and ofloxacin were associated with a significant decrease in P. aeruginosa susceptibility to ciprofloxacin.

Anti-Bacterial Agents↗
PubMed2004

Circadian and homeostatic modulation of sleep in older adults during a 90-minute day study.

STUDY OBJECTIVES: To identify age-associated changes in circadian and homeostatic characteristics of sleep in healthy elderly and young adults using electroencephalogram (EEG) power spectral analysis during a 90-minute sleep-wake schedule. DESIGN: Controlled clinical experiment. SETTING: University sleep laboratory. PARTICIPANTS: 16 older (77 +/- 5 years) and 19 younger adults (23 +/- 3 years). INTERVENTIONS: Subjects followed a 90-minute sleep-wake schedule (30 minutes in bed, 60 minutes awake) for 60 hours. Sleep was recorded for each bed-rest episode, and core body temperature was continuously recorded. The EEG power density was determined for non-rapid eye movement sleep in each bed-rest episode. Power density data were analyzed with mixed-effects models to assess rhythmic and linear components. RESULTS: Younger subjects had greater power in delta, theta, and sigma power bands across the study interval. Significant circadian rhythms were observed in delta, sigma, and beta power bands. Age-related differences in circadian modulation of EEG activity, indicated by significant interaction terms, were present in alpha and beta bands. A significant linear component was present in delta and theta power bands, with no significant age-interaction effect. CONCLUSIONS: Despite overall differences in the level of EEG power, older and younger adults exhibited similar rhythmic and linear patterns in most frequency bands. Age appears to affect circadian rhythmicity in higher EEG frequencies and homeostatic drive in lower EEG frequencies.

Adult↗
PubMed1996

HIV-1 prevalence in community-wide samples of injecting drug users in London, 1990-1993.

OBJECTIVE: To provide time-trend estimates of HIV-1 prevalence among injecting drug users (IDU) in London. DESIGN: HIV-1 prevalence and HIV testing behaviour were measured in four serial point prevalence surveys of IDU recruited at multiple sites in community-based non-treatment and drug treatment settings between 1990 and 1993. METHODS: Community subjects were recruited through social network sampling by trained indigenous interviewers; treatment subjects were interviewed at agencies. With informed consent, subjects responded to a structured questionnaire covering risk behaviour. Volunteered saliva samples were tested anonymously for anti-HIV-1. Statistical comparisons across years were examined using mixed binomial logistic and log-linear models. Pearson's chi 2 and Fisher's exact tests were also used for some two-group comparisons. RESULTS: Similar samples were recruited each year. HIV-1 prevalence rate declined from 12.8% in 1990, 9.8% in 1991, 7.0% in 1992, to 6.9% in 1993. The statistical modelling suggested that the overall trend in prevalence rates was one of decelerating decline. There was no difference in prevalence rate by gender and length of injecting. Less than one-half (46%) had received a named HIV test. Over one-half of the HIV-positive IDU were unaware of their status. CONCLUSIONS: The pattern of decline in HIV prevalence rate is attributed to changes in risk behaviour following HIV prevention interventions.

Adult↗
PubMed2003

Are there gender and race differences in cellular immunity patterns over age in infected and uninfected children born to HIV-infected women?

This study investigated whether age-related patterns of immunologic markers in 1488 uninfected (9789 measurements) and 186 infected (3414 measurements) children differed by gender and race. CD4+, CD8+, and absolute lymphocytes by HIV infection status, gender, and race were assessed using linear mixed-effects natural cubic spline models, allowing for prematurity and maternal CD4+ cell count. In uninfected children, levels of all 3 markers peaked twice in the first few months of life, declining to adult levels by around 8 years of age; uninfected boys and uninfected black children had significantly reduced CD4+ and absolute lymphocyte counts; the gender difference was especially pronounced in black children. Infected children had substantially lower levels and distinctly different patterns; with, e.g., by age 6 months CD4+ cell counts nearly 1200 per mm3 lower than in uninfected infants. Levels also significantly differed by gender and race for infected children, although for gender in the opposite direction. The gender and race differences in CD4+ levels were not explained by a general lymphocytosis nor were they confounded by treatment. These substantial differences in immunologic markers may reflect underlying genetic influence on the cellular immune system and may have implications for clinical decisions about therapeutic management.

Age Factors↗
PubMed2006

Age and size are the major covariates for prediction of levobupivacaine clearance in children.

BACKGROUND: We aimed to identify and quantify major factors describing the variability of levobupivacaine clearance in children. METHODS: Data from three published studies were used to estimate population pharmacokinetics of levobupivacaine in children who were given epidural regional blockade. Covariate analysis included weight and postnatal age (PNA). Time-concentration profile analysis was undertaken using nonlinear mixed effects models. A one-compartment linear disposition model with first order input and first order elimination was used to describe the data. RESULTS: There were 86 children (weight 9.4, sd 5.5, range 1.9-23 kg; PNA 16.1, sd 22.7, range 0.6-98 months). The population parameter estimate for volume of distribution (V) was 189 l.70 kg(-1). Clearance (CL) was 5.8 l.h(-1).70 kg(-1) at 1-month PNA and increased with a maturation half-time of 2.3 months to reach 80% of the mature value (22.1 l.h(-1).70 kg(-1)) by 6-month PNA. The between subject variability (BSV) for V and CL were 48.5% and 35.2%. Overall, 85.7% of the variability of CL was predictable. Weight alone explained 62.4% and the addition of PNA a further 23.3%. Overall, 69.2% of the variability of V was predictable and attributable to weight; V did not change with age in this cohort. The absorption half-time decreased from 0.36 h at 1-month PNA to 0.14 h (CV 48.1%) at 6-month PNA with a maturation half-time of 0.8 months. CONCLUSIONS: Size and PNA are the major contributors to clearance variability in children. These covariates should be considered when establishing safe epidural infusion regimens. Reduced clearance and slower absorption half-time contribute to delayed T(max) in neonates and young infants.

Age Factors↗
PubMedDate not supplied

Evaluation of propofol as a general anesthetic for horses.

This study provides baseline information on the potential use of propofol as a general anesthetic for horses. Using a Latin square design, propofol (2, 4, and 8 mg/kg) was administered intravenously on three separate occasions to six mature horses. Information about anesthetic induction, duration, and recovery was recorded along with results of rectal temperature, heart rate, respiratory rate, pHa, PaCO2 and PaO2. Statistical analysis included a mixed model analysis of variance, a general linear model analysis and least square means test for post hoc comparisons. A P < .05 was considered significant. The quality of induction of anesthesia varied from poor to good. Two horses were not recumbent following the lowest dose of propofol. Brief paddling limb movements occurred occasionally and unpredictably after recumbency induced by all three doses. During recovery, horses were uniformly calm and coordinated in their moves to stand. Duration of recumbency (minutes) was dose related; 15.05 +/- 1.58 (mean +/- SD) following 2 mg/kg, 31.06 +/- 5.56 following 4 mg/kg, and 47.85 +/- 13.63 following 8 mg/kg. During recumbency at all doses, heart rate significantly increased from a predrug value of 40 +/- 6 beats per minute. Substantial respiratory depression, characterized by a significant decrease in respiratory rate (from 11.7 +/- 2.9 to 3.7 +/- 1.6 breaths per minute) and increased PaCO2 (from 44.5 +/- 2.5 to 52.7 +/- 8.0 mm Hg) was seen only after 8 mg/kg. A significant decrease in PaO2 was observed throughout the recumbency induced by 8 mg/kg, and also at 3 and 5 minutes following induction of anesthesia with 4 mg/kg propofol.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗
PubMed2002

Pharmacokinetic modeling and simulations of interaction of amprenavir and ritonavir.

Data from three pharmacokinetic drug interaction studies of amprenavir and ritonavir were used to develop a pharmacokinetic interaction model using NONMEM (nonlinear mixed-effect model). A two-compartment linear model with first-order absorption best fit the amprenavir data, while a one-compartment model was used to describe the ritonavir data. The inhibition of elimination of amprenavir by ritonavir was modeled with a maximum effect (Emax) inhibition model and the observed ritonavir concentration. Monte Carlo simulation was then used to predict amprenavir concentrations for various combinations of amprenavir and ritonavir in twice-daily and once-daily dosing regimens. Simulated minimum amprenavir concentrations in plasma (Cmin) in twice-daily and once-daily dosing regimens were compared with protein binding-adjusted 50% inhibitory concentrations (IC50s) for clinical human immunodeficiency virus isolates with different susceptibilities to protease inhibitors (central tendency ratios). The model based on the first two studies predicted the results of the third study. Data from all three studies were then combined to refine the final model. The observed and simulated noncompartmental pharmacokinetic parameters agreed well. From this model, several candidate drug regimens were simulated. These simulations suggest that, in patients who have clinically failed a traditional amprenavir regimen, a regimen of 600 mg of amprenavir with 100 mg of ritonavir twice daily would result in Cmin-to-IC50 ratios similar to that of 1,200 mg of amprenavir twice daily alone for wild-type viruses. In addition, once-daily regimens that result in C(min)s above the protein binding-corrected IC50s for wild-type virus are clearly feasible.

Adolescent↗
PubMed2006

Visual stimulus-induced changes in human near-infrared fundus reflectance.

PURPOSE: Imaging studies from anesthetized feline, primate, and human retinas have revealed near-infrared fundus reflectance changes induced by visible light stimulation. In the present study, the spatial and temporal properties of similar changes were characterized in normal, awake humans. METHODS: Five normal human subjects were studied. A modified fundus camera was used to image changes in retinal reflectance of 780-nm near-infrared light imaged onto a 12-bit charge-coupled device (CCD) camera in response to a green (540 nm) visual stimulus. During 60 seconds of recording (frame rate, 3 Hz) 10 cycles were recorded, during each of which 3 seconds of blank and then 3 seconds of either vertical bar or blank stimulus was projected. The change in the average near-infrared reflectance of the stimulated retinal region relative to an equal-sized nonstimulated region (r is the ratio of reflectance between the two retinal areas) was analyzed with a mixed model for repeated measures. RESULTS: The mixed model showed a significant average decrease in r of 0.14% (95% CI, -0.25 to -0.03) over all subjects induced by bar stimulus cycles, with a gradual return to baseline after stimulus offset, compared with only a 0.04% (95% CI, -0.11-+0.20) decrease in r induced by blank, nonstimulated cycles. The mixed model for individuals showed a decreasing linear trend in r over time during bar stimulation, but no decrease for blank cycles in three of five subjects. CONCLUSIONS: There was a localized decrease in reflectance in response to 780-nm near-infrared light in the retinal region exposed to a visual stimulus, which was significant in three of five subjects. It is presumed that the reflectance change represents the functional activity of the retina in response to a visual stimulus.

Adult↗
PubMed2004

The characteristics of quality of life impairment in adult growth hormone (GH)-deficient survivors of cancer and their response to GH replacement therapy.

We studied 50 (27 women and 23 men) GH-deficient (GHD) cancer survivors and 47 (24 women and 23 men) GHD patients with pituitary pathologies. All GHD patients were considered for GH replacement on the basis of subjectively poor quality of life (QOL). Primary outcome measures were scores of QOL instruments psychological general well-being schedule (PGWB) and assessment of GH deficiency in adults (AGHDA) at baseline and early (6-13 months) and long-term (24-77 months) treatment follow-up. Of secondary interest were six PGWB domains. Linear mixed effect regression was used to model each QOL outcome. The groups differed with respect to three covariates: age, gender, and body mass index. These variables were included in all fitted models. Baseline scores for PGWB and AGHDA were not different between groups. Ranking of PGWB domains were similar between groups at baseline (lowest domain, vitality). The pattern of change in mean scores for all outcome measures from baseline did not differ between groups (P = 0.86). All QOL variables improved significantly with treatment [estimated mean change +/- se: PGWB, 16.2 +/- 1.7; AGHDA, -6.2 +/- 0.6; PGWB domains (transformed percentage scales): anxiety, 12.4 +/- 1.7; depression, 14.1 +/- 2.1; health, 12.4 +/- 1.7; self-control, 11.3 +/- 2.0; well-being, 15.2 +/- 1.7; vitality, 22.5 +/- 2.0 (vitality, greatest change)]. There was no evidence of group difference in early follow-up or long-term follow-up means for any outcome variable. The QOL in adult GHD cancer survivors was comparable to that in GHD adults with pituitary pathologies and improved with GH replacement in a similar manner. We conclude that QOL impairment in adult GHD cancer survivors appears mainly related to GHD rather than cancer diagnosis and treatment.

Adenoma↗
PubMed2006

Do changes in body mass index percentile reflect changes in body composition in children? Data from the Fels Longitudinal Study.

OBJECTIVE: Our aim was to examine the degree to which changes in BMI percentile reflect changes in body fat and lean body mass during childhood and how age and gender affect these relationships. METHODS: This analysis used serial data on 494 white boys and girls who were aged 8 to 18 years and participating in the Fels Longitudinal Study (total 2319 observations). Total body fat (TBF), total body fat-free mass (FFM), and percentage of body fat (%BF) were determined by hydrodensitometry, and then BMI was partitioned into its fat and fat-free components: fat mass index (FMI) and FFM index (FFMI). We calculated predicted changes (Delta) in FMI, FFMI, and %BF for each 10-unit increase in BMI percentile using mixed-effects models. RESULTS: FFMI had a linear relationship with BMI percentile, whereas FMI and %BF tended to increase dramatically only at higher BMI percentiles. Gender and age had significant effects on the relationship between BMI percentile and FFMI, FMI, and %BF. Predicted Delta%BF for boys 13 to 18 years of age was negative, suggesting loss of relative fatness for each 10-unit increase in BMI percentile. CONCLUSIONS: In this longitudinal study of white children, FFMI consistently increased with BMI percentile, whereas FMI and %BF had more complicated relationships with BMI percentile depending on gender, age, and whether BMI percentile was high or low. Our results suggest that BMI percentile changes may not accurately reflect changes in adiposity in children over time, particularly among male adolescents and children of lower BMI.

Adolescent↗
PubMed2000

Comparative study between children with and without cleft lip and cleft palate, part 1: cephalometric analysis.

OBJECTIVE: This study was conducted to compare craniofacial relationships, position, and curvature of the cervical spine between children with cleft lip and cleft palate who had been operated on and children without clefts. METHOD: This study was performed in 28 children with mixed dentition. They were divided into two groups. The study group included 14 children with unilateral operated cleft lip and cleft palate, ranging in age from 6 to 12 years, who clinically presented with a short upper lip, abnormal lip seal, and inhibition of sagittal development of the midface that was radiographically assessed. The control group included 14 children without clefts, ranging in age from 8 to 11 years. All of them had normal lip seal, nasal breathing, and a clinically normal body posture. DESIGN: A lateral craniocervical radiograph in a self-balanced natural head position in an erect posture, and without using a head holder, was taken for each child of both groups, with the mandible in maximum intercuspation and lips in habitual posture. The true vertical was marked on all the films. Specific angular and linear dimensions were used to assess the craniocervical relationships, as were the position of the cervical spine, its curvature, or both. RESULTS AND CONCLUSIONS: The study group presented a significant increase in the extension of the head on the neck, forward position of the cervical spine, and a decrease in the curvature of the cervical spine in comparison with the children without clefts. These results are more relevant considering that the study group also presented higher significant values of lower facial height than children without clefts.

Cephalometry↗
PubMed2005

Genetic analysis of age at first service, return rate, litter size, and weaning-to-first service interval of gilts and sows.

The aim of this study was to estimate genetic parameters of seven traits related to sow reproductive performance. Data on all Norwegian Landrace pigs (NL) born in nucleus herds and raised in nucleus or multiplying herds from 1990 to 2000 were extracted from the Norwegian national recording scheme. Reproductive traits investigated were age at first service (AFS), return rate in gilts (RRg), age at first farrowing (AFF), live-born piglets in the first litter (NBA1), interval from weaning to first service after first litter (WTS1), return rate after first litter (RR1), live-born piglets in the second litter (NBA2), and interval from weaning to first service after second litter (WTS2). After editing, the data set comprised 12,583 to 56,042 records, depending on the trait. A mixed linear and a joint linear threshold animal model were used to estimate (co)variance components. A full Bayesian approach via Gibbs sampling was adopted. The statistical model used for analysis included contemporary groups of herd-year (-season), purebred or crossbred litter, single or double insemination, mating type, parity in which the animal was born, a regression on lactation length, and an additive genetic effect. Neither the estimated heritabilities nor the genetic correlations differed much between the two approaches, but there was a tendency for higher genetic correlations using the joint linear threshold model approach. Average heritabilities were as follows: AFS = 0.31; RRg = 0.03; RR1 = 0.02; NBA1 = 0.12; NBA2 = 0.14; WTS1 = 0.08; and WTS2 = 0.03. The highest genetic correlations were estimated between NBA1 and NBA2 (r(g) = 0.95), RR1 and WTS1 (r(g) = 0.93), and between WTS1 and WTS2 (r(g) = 0.78). The estimated genetic correlation between NBA and WTS were close to zero. Selection for increased NBA will slightly increase AFS and reduce the probability of a return. Selection for decreased AFS will have a favorable effect on WTS intervals; however, selection for decreased AFS seems to have an unfavorable effect on return rate both on gilts and sows. Conversely, selection for decreased WTS intervals will reduce the probability of a return. Potential selection candidates to include in a multivariate fertility index are AFS, NBA, and WTS1. Due to the low heritability and low, but favorable, genetic correlations to NBA and WTS, RR is not recommended as a selection candidate.

Age Factors↗
PubMed2000

[The predication equation of the permanent canine and premolar crown].

OBJECTIVE: It is important to predict mesiodistal crown diameter of the permanent canines and premolars in the mixed dentition, which helps to determine malocclusion and its further development. But there is still no article about this equation of Chinese used to predict mesiodistal crown diameter of cuspids and premolars. This research is to measure mesiodistal crown diameters, to study relationship between lower incisors and canines and premolars, and to provide the most accurate and easy basis in orthodontic diagnosis and treatment for Chinese people. METHODS: 140 Chinese students (60 male, 80 female) who were from eighteen to twenty-five years old without orthodontic history Chengdu were randomly collected in. All teeth must be free of visible malform, aberration, and fully erupted. Impressions were taken, and measurements were made, parallel to the occlusal plane at the greatest mesiodistal width of each tooth on dental cast with electronic caliper (0.01 mm). Each tooth was measured twice and the average of the two readings was taken as the dimension for that individual tooth. Mesiodistal crown diameters were statistically analyzed with t-test and linear regression, using the SAS (Statistic Analyses System) computer package. RESULTS: It was found that mesiodistal crown diameters had significantly statistical difference in gender. Hence the mesiodistal crown diameters were assessed and investigated separately for the male and the female. It was also found that the total mesiodistal crown diameter of lower incisors was closely correlated with the total mesiodistal crown diameter of canines and premolars. The correlation coefficients between the independent variable and dependent variables were 0.599 for upper canines and premolars and 0.654 for lower canines and premolars in the males and 0.586 and 0.635, respectively, in the females. The P were found to be less than 0.001 for both arches. The correlation coefficients had significantly statistical difference. CONCLUSION: The equations predicting overall mesiodistal crown diameters of upper and lower unerupted canines and premolars for male and female Chinese people were established respectively: Maxillary (y = 10.87 + 0.51 x (male)), y = 11.88 + 0.46 x (female), Mandibular (y = 10.36 + 0.50 x (male), y = 10.03 + 0.49 x (female)), y (total mesiodistal crown diameter of canines and premolars), and x (total mesiodistal crown diameter of lower incisors).

Adolescent↗
PubMed2004

Correlates of sleep-wake patterns among children and young adolescents in Taiwan.

STUDY OBJECTIVE: To determine correlates of morning and evening sleep-wake patterns in a community sample of children. DESIGN: A school-based cross-sectional survey. PARTICIPANTS: Sample included 1572 students, grades 4 to 8 (response rate, 98.4%), using a multistage sampling method. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Student participants completed a Sleep Habits Questionnaire, which included sleep schedules, a mood scale, substance use, the morningness/eveningness (M/E) scale, pubertal development scale, sleep disturbance scale, and parental monitoring scale. The morning (n = 367) and evening (n = 364) groups were operationally defined as participants who scored in the top or bottom 25% of the M/E scale, respectively. Linear mixed and tree-based classification models were used to explore correlates of sleep-wake patterns. Our results showed the evening type was associated with older school grade level, increased coffee drinking, moodiness, decreased parental monitoring, daytime sleepiness, and several sleep disturbances, including early insomnia, fear of sleeping in darkness, bedwetting, and going to bed later than 3 am. The 2 most potent discriminators between evening and morning subtypes were higher grade level, an index of age, and moodiness. The association of moodiness with the evening type was greater in boys than girls. CONCLUSIONS: These findings suggest that further research should address explanations for the association between evening type and mood and anxiety symptoms, including order of the effects, developmental factors, environmental determinants of sleep time such as school start time and parental bedtime monitoring, and circadian maturation.

Adolescent↗
PubMed2005

Mixed-effects variance components models for biometric family analyses.

Recent substantive research on biometric analyses of twin and family data has used both a biometric path analysis model (PAM) and a biometric variance components model (VCM). Methodological research on these same topics have suggested benefits of using linear structural equation model algorithms (SEMA) as well as mixed effect multilevel algorithms (MEMA). To better understand the potential similarities and differences among these approaches we first highlight the algebraic equivalence between the standard biometric PAM and the corresponding biometric VCM models for family data. Second, we demonstrate how several SEMA programs based on either the PAM or VCM approach produce equivalent estimates for all phenotypic and biometric parameters. Third, we show how the biometric VCM approach (but not the PAM approach) can be easily programmed using current MEMA programs (e.g., SAS PROC MIXED). We then expand the scope of these different approaches to include measured covariates, observed variable interactions and multiple relatives within each family. MEMA software is compared to SEMA software for programming complex models, including the flexibility of data input, treatment of missing data, inclusion of covariates, and ease of accommodating varying numbers of observations (per family or individual).

Algorithms↗