Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “multilevel analysis”

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 487 records · Page 27Linked to original sources
PubMed2002

A method for estimating within-patient variability in maximal urinary flow rate adjusted for voided volume.

OBJECTIVES: To investigate whether volume adjustment can be used to reduce the within-patient variability of the maximal urinary flow rate (Qmax) without affecting the variability between patients. METHODS: We analyzed 2049 urinary flow curves of 208 men with lower urinary tract symptoms suggestive of bladder outlet obstruction and studied the relation between Qmax and voided volume (VV) in individual patients using multilevel regression analysis. RESULTS: In agreement with most previous studies, we found a hyperbolic relation between the VV and Qmax. Although hyperbolic on average, the slope of the regression line relating the VV to Qmax differed substantially across individual patients. In some patients, Qmax even tended to be lower with an increased VV. CONCLUSIONS: The reproducibility of Qmax is poor, in part because of its dependence on the VV. The current methods to adjust Qmax for VV, such as the Siroky nomogram, minimize between-patient dependency, whereas our findings emphasize the importance of within-patient variability. A common approach to adjust Qmax for VV, however, is not feasible, because the relation of Qmax to VV differs substantially across patients. The only valid, although impractical option, remains to record a large number of urinary flow curves for each patient.

Diagnostic Techniques, Urological↗
PubMed1997

Analysis of a randomly assorted cDNA library from BW 5147 lymphoid cells. Frequency estimates based on computer aided concatenation matching of 2D gel polypeptide products.

A cDNA library was divided into 291 sectors of low complexity, 800-1000 recombinant phage plaques per sector. Aliquots of DNA from sectors prepared from high titer phage were subjected to in vitro transcription using T7 polymerase and thereafter RNA was translated in a cell-free rabbit reticulocyte system in the presence of [35S] methionine. The resulting polypeptides were separated by 2D gel electrophoresis. Radiofluorographs of the gels prepared from 10 sectors were subjected to scanning and image analysis. A multilevel spot matching procedure was employed allowing us to recognise spot occurrence in the 10 sectors. The number of detected polypeptide spots per sector varied between 147 and 325. Overall, 1082 different spots were counted totalling 1983 spots considering multiple entries. The distribution of the spots and the frequency distribution of the RNA population among the 10 sectors are shown. The highest detected frequency is 10(-2), while one half of the RNA molecular species are present at a frequency of 10(-3) or lower.

Animals↗
PubMed1999

Quality of life in depression: daily life determinants and variability.

Identifying daily influences on subjective well-being can be helpful in understanding the burden of depression. This study used experience sampling methodology (ESM) to examine the contribution of mood states, physical complaints and enjoyment of activities to a momentary measure of quality of life (mQoL), assessed by responses to the question 'In general, how is it going with you right now?' Sixty-three depressed and 22 healthy control subjects completed ESM self-reports during daily activities, 10 times per day for 6 days. In comparison to control subjects, depressed subjects had lower levels of mQoL, positive mood, and enjoyment of activity, higher negative mood, and more frequent and severe complaints. Depressed subjects were more likely than control subjects to be doing nothing and less likely to be engaged in work. Multilevel regression analysis showed that positive mood and enjoyment of the current activity were associated with higher mQoL, whereas negative mood and complaints were associated with lower mQoL. In depressed subjects, mQoL was more variable over time than in control subjects. In contrast to the ESM results, only negative mood and depression were significant predictors of global measures of QoL. We conclude that QoL has important situational determinants that can in part explain the impact of depression on daily functioning and well-being.

Adolescent↗
PubMed1999

Influence of farm, feed-producer and season on incidence of gastrointestinal disorders in Danish farm mink.

The distribution of gastrointestinal disorders in mink in Danish farms is presented based on data collected in a longitudinal design. The time at risk was from weaning in June until pelting in November. The occurrence of gastrointestinal disorders after weaning of the mink kits together with the distribution within farms was studied. The period of highest risk was in the months immediately after weaning (July and August). More than 17% of the farms recorded GI disorders among > or = 10% of pairs of animals. A multilevel statistical analysis showed that besides the effect of time after weaning, a significant part of the variation in the incidence could be attributed to the farm and feed-producer. The potential for bias is discussed.

Age Factors↗
PubMed2003

General multilevel linear modeling for group analysis in FMRI.

This article discusses general modeling of multisubject and/or multisession FMRI data. In particular, we show that a two-level mixed-effects model (where parameters of interest at the group level are estimated from parameter and variance estimates from the single-session level) can be made equivalent to a single complete mixed-effects model (where parameters of interest at the group level are estimated directly from all of the original single sessions' time series data) if the (co-)variance at the second level is set equal to the sum of the (co-)variances in the single-level form, using the BLUE with known covariances. This result has significant implications for group studies in FMRI, since it shows that the group analysis requires only values of the parameter estimates and their (co-)variance from the first level, generalizing the well-established "summary statistics" approach in FMRI. The simple and generalized framework allows different prewhitening and different first-level regressors to be used for each subject. The framework incorporates multiple levels and cases such as repeated measures, paired or unpaired t tests and F tests at the group level; explicit examples of such models are given in the article. Using numerical simulations based on typical first-level covariance structures from real FMRI data we demonstrate that by taking into account lower-level covariances and heterogeneity a substantial increase in higher-level Z score is possible.

Algorithms↗
PubMedDate not supplied

Segmental pedicle screw fixation or cross-links in multilevel lumbar constructs. a biomechanical analysis.

BACKGROUND CONTEXT: The placement of segmental pedicle screws and cross-links in short segment posterior pedicle screw constructs has been shown to increase the construct stiffness in some planes. To date, no studies have looked at the contributions of segmental pedicle screw and cross-link placement in longer constructs. PURPOSE: To evaluate the influence of segmental pedicle screw and/or cross-link placement on flexion/extension, lateral bending and axial torsion stiffness in two- and three-level posterior pedicle screw fixation constructs. STUDY DESIGN/SETTING: An in vitro biomechanical analysis of two- and three-level posterior pedicle screw constructs with and without segmental fixation and/or cross-links was performed using calf lumbar spines. Stiffness of the constructs was compared. METHODS: Six calf lumbar specimens were used to test stiffness in one-, two- and three-level posterior pedicle screw fixation constructs in 12 configurations. A custom-made, four-axis spine simulator applied pure cyclical (+/-5 Nm) flexion/extension, lateral bending and axial torsion moments at 0.1 Hz under a constant 50-N axial compressive load. The stiffness of each construct was calculated about each axis of rotation. Data were analyzed using nonparametric techniques with statistical significance determined at alpha less than .05. RESULTS: The stiffness of the instrumented spines were significantly greater than the noninstrumented intact spines in all loading conditions for one-, two- and three-level constructs. There were no significant changes in flexion/extension stiffness with the addition of either the cross-links or the segmental pedicle screws. In lateral bending, the addition of segmental pedicle screws significantly increased the stiffness in the two- and three-level constructs. The addition of two cross-links increased lateral bending stiffness in the longer three-level constructs, with little change in the two-level constructs. In axial torsion, the progressive addition of cross-links showed a tendency toward increased stiffness in both the two- and three-level constructs. Segmental pedicle screws further increased torsional stiffness of the longer, three-level constructs. CONCLUSIONS: As the use of segmental spinal instrumentation progresses from one to two and three levels, the contribution of cross-links and segmental pedicle screws to the overall construct stiffness increases.

Animals↗
PubMed2001

Factors associated with unfavourable birth outcomes in Kenya.

Studies addressing factors associated with adverse birth outcomes have almost exclusively been based on hospital statistics. This is a serious limitation in developing countries where the majority of births do not occur within health facilities. This paper examines factors associated with premature deliveries, small baby's size at birth and Caesarean section deliveries in Kenya based on the 1993 Kenya Demographic and Health Survey data. Due to the hierarchical nature of the data, the analysis uses multilevel logistic regression models to take into account the family and community effects. The results show that the odds of unfavourable birth outcomes are significantly higher for first births than for higher order births. Furthermore, antenatal care (measured by frequency of antenatal care visits and tetanus toxoid injection) is observed to have a negative association with the incidence of premature births. For the baby's size at birth, maternal nutritional status is observed to be a predominant factor. Short maternal stature is confirmed as a significant risk factor for Caesarean section deliveries. The observed higher odds of Caesarean section deliveries among women from households of high socioeconomic status are attributed to the expected association between socioeconomic status and the use of appropriate maternal health care services. The odds of unfavourable birth outcomes vary significantly between women. In addition, the odds of Caesarean section deliveries vary between districts, after taking into account the individual-level characteristics of the woman.

Adolescent↗
PubMed2005

Family background, schooling and childlessness in Australia.

Using data from Wave 1 of the Household Income and Labour Dynamics in Australia (HILDA) survey, this paper analyses the extent to which childlessness among Australian women aged 40-54 years varies according to the size and type of family in which they were brought up, and the level and type of schooling they had. Multilevel logistic analysis shows that having been educated in a non-government school, having stayed at school to year 12, having a small number of siblings, at age 14 having a father who was either dead or absent, at age 14 having a father who was employed in a professional occupation, or being a migrant from North or West Europe, North America, East Asia or South-East Asia, all are significantly associated with higher rates of childlessness among women in the 40-54 years age range. The effects of these early lifecourse variables on marital and socioeconomic status in later life, and hence on childlessness, are also considered. The implications of the findings for fertility trends and for Australia's public debate are discussed.

Adult↗
PubMed2006

Changes in perceptions of quality of, and access to, services among clients of a fractional franchise network in Nepal.

With declining levels of international donor funding for financing reproductive health programmes, developing country governments and international donors are looking towards private sector strategies to expand the supply of quality reproductive health services. One of the challenges of a health franchise is to improve the quality of services provided by independent private practitioners. Private providers are more likely to abide by the quality standards set by a franchiser if they see a financial benefit resulting from franchise participation. This study was conducted to measure whether (a) there were improvements in perceived quality of care and perceived access to health facilities once these facilities became part of a franchise and (b) improvements in perceived quality and perceived access were associated with increased client loyalty to franchised clinics. Franchisees were given basic reproductive health training for seven days and services marketing training for two days. Exit interviews were conducted with male and female clients at health facilities. A pre-test measurement was taken in April 2001, prior to the start of project activities. A post-test measurement was taken in February/March 2002, about 9 months after the pre-test. Multilevel regression analysis, which takes the hierarchical structure of the data into account, was used for the analysis. After taking provider-level variation into account and controlling for client characteristics, the analyses showed significant improvements in perceived quality of care and perceived access to services. Private provider participation in a franchise network helps improve client perceptions of quality of, and access to, services. Improvements in client perceptions of quality and access contribute to increased client loyalty to franchised clinics. Once increased client loyalty translates into higher client volumes, providers are likely to see the benefits of franchise participation. In turn, this should lead to increased provider willingness to remain part of the franchise and to abide by the standards of quality set by the franchiser.

Adult↗
PubMed2002

Prenatal life and post-natal psychopathology: evidence for negative gene-birth weight interaction.

BACKGROUND: Many studies suggest that pregnancy and birth complications (PBCs) are environmental risk factors for child psychopathology. However, it is not known whether the effects of PBCs occur independently of genetic predisposition. The current study examined the possibility of gene-environment interaction in a twin design. METHOD: The East Flanders Prospective Twin Survey prospectively records the births of all twin pairs born in East Flanders, Belgium. The current study included 760 twin pairs aged 6-17 years. Multilevel regression analysis was used to assess the effects of several PBCs collected around the time of birth. Using structural equation modelling, ACE models assuming additive genetic (A), shared environmental (C) and unique environmental (E) influences, were compared in order to examine whether the contribution of genetic factors to parent-rated child problem behaviour varied as a function of exposure to dichotomously and continuously defined PBCs. RESULTS: A main independent effect of lower birth weight, corrected for gestational age (small for gestational age--SGA), on child problem behaviour was found. In addition, there was an interaction between genetic influence and SGA, in that being smaller for gestational age resulted in less influence of additive genetic factors on individual differences in problem behaviour. CONCLUSIONS: Results are suggestive of negative gene-birth weight interaction. Children who are SGA are less sensitive to the genetic effects, and those with high genetic vulnerability are less sensitive to the effects of being SGA in bringing about post-natal mental health effects.

Adolescent↗
PubMed2004

Personality as a predictor of weight loss maintenance after surgery for morbid obesity.

OBJECTIVE: Personality characteristics are assumed to underlie health behaviors and, thus, a variety of health outcomes. Our aim was to examine prospectively whether personality traits predict short- and long-term weight loss after laparoscopic adjustable gastric banding. RESEARCH METHODS AND PROCEDURES: Of patients undergoing laparoscopic adjustable gastric banding, 168 (143 women, 25 men, 18 to 58 years old, mean 37 years, preoperative BMI 45.9 +/- 5.6 kg/m(2)) completed the Dutch Personality Questionnaire on average 1.5 years before the operation. The relationship between preoperative personality and short- and long-term postoperative weight loss was determined using multilevel regression analysis. RESULTS: The average weight loss of patients progressively increased to 10 BMI points until 18 months after surgery and stabilized thereafter. A lower baseline BMI, being a man, and a higher educational level were associated with a lower weight loss. None of the personality variables was associated with weight outcome at short-term follow-up. Six of seven personality variables did not predict long-term weight outcome. Egoism was associated with less weight loss in the long-term postoperative period. The effect sizes of the significant predictions were small. DISCUSSION: None of the personality variables predicted short-term weight outcome, and only one variable showed a small and unexpected association with long-term weight outcome that needs confirmation. This suggests that personality assessment as intake psychological screening is of little use for the prediction of a poor or successful weight outcome after bariatric surgery.

Adolescent↗
PubMed2005

Distinguishing adaptive from nonadaptive genetic differentiation: comparison of Q(ST) and F(ST) at two spatial scales.

Genetic differentiation in 20 hierarchically sampled populations of wild barley was analyzed with quantitative traits, allozymes and Random Amplified Polymorphic DNAs (RAPDs), and compared for three marker types at two hierarchical levels. Regional subdivision for both molecular markers was much lower than for quantitative traits. For both allozymes and RAPDs, most loci exhibited minor or no regional differentiation, and the relatively high overall estimates of the latter were due to several loci with exceptionally high regional differentiation. The allozyme- and RAPD-specific patterns of differentiation were concordant in general with one another, but not with quantitative trait differentiation. Divergent selection on quantitative traits inferred from very high regional Q(ST) was in full agreement with our previous results obtained from a test of local adaptation and multilevel selection analysis. In contrast, most variation in allozyme and RAPD variation was neutral, although several allozyme loci and RAPD markers were exceptional in their levels of regional differentiation. However, it is not possible to answer the question whether these exceptional loci are directly involved in the response to selection pressure or merely linked to the selected loci. The fact that Q(ST) and F(ST) did not differ at the population scale, that is, within regions, but differed at the regional scale, for which local adaptation has been previously shown, implies that comparison of the level of subdivision in quantitative traits, as compared with molecular markers, is indicative of adaptive population differentiation only when sampling is carried out at the appropriate scale.

Adaptation, Biological↗
PubMed2003

Carbon dioxide elimination during laparoscopy in children is age dependent.

UNLABELLED: The absorption of carbon dioxide (CO2) used for positive pressure pneumoperitoneum may lead to an increased CO2 load. CO2 elimination during laparoscopy has not been investigated previously in paediatrics. The aim of this study was to characterise the pattern of CO2 elimination during laparoscopic surgery in infants and children. METHODS: Twenty children undergoing laparoscopy and 19 children undergoing laparotomy for elective abdominal operations were studied. Pneumoperitoneum was achieved using insufflation of unheated CO2. CO2 elimination (metabolically produced + absorbed; milliliters per kilogram per minute) was measured minute by minute during the operation by indirect calorimetry. End-tidal CO2 (kPa) was recorded every 10 minutes. The above variables were assessed before CO2 insufflation, during pneumoperitoneum, and after desufflation. RESULTS: Before insufflation, CO2 elimination was 4.6 +/- 0.3 ml/kg/min and increased after 15 minutes of pneumoperitoneum to 5.2 +/- 0.3 (P <.001). Post desufflation, CO2 elimination decreased toward preinsufflation values, but did not return to baseline by the end of operation (5.8 +/- 0.3; P <.001). End-tidal CO2 was 4.7 +/- 0.2 preinsufflation, peaked at 1 hour (5.3 +/- 0.2; P <.001) and subsequently decreased in response to ventilatory adjustments. The total amount of CO2 insufflated was positively correlated with patient age (r2 = 0.27; P <.01). CO2 elimination was age related, as indicated by multilevel model analysis and by negative correlations between maximum increase in CO2 elimination and both age (r2 = 0.27; P <.01) and weight (r2 = 0.29; P <.01). These data suggest that the younger or smaller the child, the larger the increase in CO2 elimination. Seven patients (35%) responded to desufflation with a sharp transient increase in CO2 elimination, which did not appear to be related to patient age, length of pneumoperitoneum, abdominal pressure, or type of operation. CONCLUSIONS: During pneumoperitoneum, younger children absorb proportionately more CO2 than older individuals. The short-lived increase in CO2 elimination postdesufflation may be related to an increase in venous return from the lower limbs after release of the abdominal pressure. These findings suggest that small children warrant close monitoring during laparoscopy and during the immediate postoperative period.

Adolescent↗
PubMed2006

Longitudinal reference ranges for estimated fetal weight.

OBJECTIVE: The aims of the present study were to establish reference ranges for the growth of estimated fetal weight (EFW) between gestational weeks 20 and 42 and to determine the effect of fetal and maternal factors. METHODS: This prospective longitudinal study was based on 634 low-risk pregnancies and a total of 1799 examinations. Gestational age was computed from last menstrual period. Head circumference, abdominal circumference, and femur length were measured using ultrasound, and EFW was calculated using the formula of Combs et al. The statistical analysis was based on regression analysis and multilevel modeling. RESULTS: Intrauterine growth expressed by EFW showed a continuous pattern until term. Males were calculated to be 5% heavier than female fetuses at 20 gestational weeks and 3% at 40 weeks. Otherwise, the fetal and maternal effects on intrauterine growth correspond to a weight shift of 1.3% for breech/nonbreech, 2.5% for each increase in maternal height tertile, and -4% for smoking/nonsmoking. Maternal age higher than 34 years had a significant increased EFW of 4.5% compared with maternal age less than 24 years. Cephalic index in the third tertile had a 1.1% lower EFW compared with the first tertile. Maternal weight, body mass index, and parity did not influence the EFW. Terms for customization to individualize the growth patterns are presented. CONCLUSIONS: The present growth chart is recommended as robust reference ranges for assessing EFW and growth. Fetal and maternal variables can be added into the models to individualize the prediction of EFW.

Adult↗
PubMed2006

Factors related to medication adherence in memory disorder clinic patients.

Medication adherence is a substantial problem in the elderly. It may be even more important among elderly persons with memory problems, since other factors that lead to non-adherence may be compounded with the memory problems themselves. The objective was to determine whether a model that integrates research on medication adherence from several research domains is useful in understanding adherence in elderly patients. The methodology involved a cross-sectional observational study using a convenience sample of 63 patients drawn from a university-affiliated outpatient memory disorders clinic. The primary measure of medication adherence was caregivers' reports of patients' medication adherence. Patients and their caregivers were asked questions assessing their beliefs about the seriousness of each condition for which a medication was prescribed and the likely outcome of that condition without treatment. Additional data collected included presence of side effects, total number of medications taken, and patients' mood and cognitive status. Multilevel path analysis confirmed several model-based predictions. Caregivers' reports of adherence were predicted by estimates of disease outcome, the presence of side effects, and patients' relying on themselves to remember to take medications. Results partially confirm the integrative model in understanding medication adherence in these patients. Patients' beliefs about the likely effect of medication treatment for their condition and the presence of side effects influence reported medication adherence. Results thus suggest that efforts to educate patients about the likely response of their medical condition to treatment and to assess and deal with medication side effects might improve patient adherence.

Aged↗
PubMed2006

Influences affecting adolescent smoking behavior in China.

This study examined multiple influences on the use of tobacco by adolescents in China. Using the theory of triadic influences as a guide, we selected interpersonal, attitudinal/cultural, and intrapersonal constructs from baseline data to predict adolescent smoking 1 year later. We used prospective data from middle and high school students (N = 11,583) and their parents from the China Seven Cities Study, a longitudinal study that is evaluating the effects of changing economic and social factors on health behaviors including tobacco use. A multilevel regression analysis provided some support that each of the influences in the theory of triadic influences affects adolescent smoking in China. After adjusting for important confounders including age, gender, socioeconomic status, and smoking behaviors (lifetime and past 30-day) at baseline, we found significant risk factors within each of the three categories, including interpersonal influences (parental monitoring, good friend smoking, and peer smoking), attitudinal/cultural influences (school academic ranking, initial liking of smoking, and the meaning of smoking), and intrapersonal influences (susceptibility to smoking, and low self-confidence to quit smoking). Results suggest that the etiology of smoking among adolescents in China might be similar to that observed in western countries and that some of the techniques used successfully in prevention programs in those countries might be useful guides when developing prevention programs in China.

Adolescent↗
PubMed2003

Neighborhood mechanisms and the spatial dynamics of birth weight.

This study addresses two questions about why neighborhood contexts matter for individuals via a multilevel, spatial analysis of birthweight for 101,662 live births within 342 Chicago neighborhoods. First, what are the mechanisms through which neighborhood structural composition is related to health? The results show that mechanisms related to stress and adaptation (violent crime, reciprocal exchange and participation in local voluntary associations) are the most robust neighborhood-level predictors of birth weight. Second, are contextual influences on health limited to the immediate neighborhood or do they extend to a wider geographic context? The results show that contextual effects on birth weight extend to the social environment beyond the immediate neighborhood, even after adjusting for potentially confounding covariates. These findings suggest that the theoretical understanding and empirical estimation of 'neighborhood effects' on health are bolstered by collecting data on more causally proximate social processes and by taking into account spatial interdependencies among neighborhoods.

Birth Weight↗
PubMed2005

The relative influence of individual and contextual socio-economic status on consumption of fruit and soft drinks among adolescents in Europe.

BACKGROUND: The number of studies among children and adolescents that focus on socio-economic differences in food habits is limited. Moreover, most are done in only one country and often include a non-representative sample. The present study examines whether socio-economic differences in the consumption of fruit and soft drinks can be found among young adolescents in a wide range of European countries. METHODS: Multilevel statistical analysis of 114 558 school-pupils aged 11, 13 and 15 from 28 countries participating in the WHO collaborative cross-national study of Health Behaviours among School-aged Children 2001-2002. The individual outcomes were daily fruit and soft drink consumption and the socio-economic predictors at the individual level were occupation of the head of household and family material wealth. Family material wealth was aggregated at the country level to operationalize country-level socio-economic status. RESULTS: In general, girls and younger pupils consumed fruit more often and soft drinks less often. Significant between-school, between-country and between-region differences were found. Fruit consumption increased with family material wealth and higher parental occupational status. Soft drink consumption was lower among pupils of higher parental occupational status in Northern, Southern and Western European countries, but not in Central and Eastern European countries. Only in Central and Eastern European countries was a significant increase in soft drink consumption with increasing family affluence found. The country level of family affluence did not seem to have an effect on either outcome variable. CONCLUSION: The findings underscore the importance of socio-economic factors in relation to the food habits of young adolescents.

Adolescent↗