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PubMed1997

Biomechanical analysis of multilevel fixation methods in the lumbar spine.

STUDY DESIGN: The authors measured and compared the stiffness of cadaveric lumbar spines stabilized with several anterior interbody fusion devices. The information obtained provides a foundation for determining how methods of anterior lumbar fixation can maximize rigidity and promote development of bony fusion. OBJECTIVES: To compare the utility of three anterior spinal instrumentation systems for stabilizing the lumbar spine. SUMMARY OF BACKGROUND DATA: Anterior spinal instrumentation is used to prevent progressive spinal deformity and maintain correction after spinal fusion surgery. Newer instrumentation systems developed for anterior interbody fusions can be inserted by minimally invasive procedures. The stability of these systems has not been tested adequately in human cadaveric specimens. METHODS: Fusion constructs were evaluated in 12 human cadaveric specimens sequentially loaded in axial compression and torsion, flexion and extension, and lateral bending. The fusion constructs used were 1) two anterior bilateral threaded interbody fusion devices, 2) lateral hollow interbody screws (Texas Scottish Rite Hospital-B screws), and 3) femoral allograft and conventional anterior Texas Scottish Rite Hospital instrumentation. RESULTS: The construct with Texas Scottish Rite Hospital-B screws connected by a rod produced stiffness comparable with that produced by conventional Texas Scottish Rite Hospital instrumentation with femoral ring allografts. The threaded interbody fusion device stiffness tested in axial rotation was comparable with that achieved with Texas Scottish Rite Hospital instrumentation. CONCLUSIONS: Our data demonstrate the effectiveness of threaded interbody fusion device and the Texas Scottish Rite Hospital-B screw in immobilizing the L3-L4 and L4-L5 disc spaces. Rigidity of fixation in the lumbar spine may aid in the maintenance of lordosis.

Absorptiometry, Photon↗
PubMed2006

Schools, parents, and youth violence: a multilevel, ecological analysis.

Using data from the National Longitudinal Study of Adolescent Health (Add Health), this study utilized an ecological approach to investigate the joint contribution of parents and schools on changes in violent behavior over time among a sample of 6,397 students (54% female) from 125 schools. This study examined the main and interactive effects of parent and school connectedness as buffers of violent behavior within a hierarchical linear model, focusing on both students and schools as the unit of analysis. Results show that students who feel more connected to their schools demonstrate reductions in violent behavior over time. On the school level, our findings suggest that school climate serves as a protective factor for student violent behavior. Finally, parent and school connectedness appear to work together to buffer adolescents from the effects of violence exposure on subsequent violent behavior.

Adolescent↗
PubMed1975

[Diagnostic value of isocount scanning in cerebrovascular diseases (author's transl)].

In the previous report the theoretical background and technical details of the isocount scanning were described. Based on clinical experiences of various brain diseases, the newly developed scanning method was confirmed to be more useful than the conventional scintiscanning. Besides the new scanning method, a new display system was also developed for the sake of more precise analysis of the isocount scanned data. This display method is called multilevel analysis or multilevel slicing of the scanned data. In the present investigation, this method was applied to thirty-two cases of cerebrovascular diseases, including seven cases of cerebral arterio-venous malformation, four cases of hypertensive intracerebral hemorrhage and twenty-one cases of cerebral infarction, positive rates being 86%, 100% and 90% respectively. In case of arterio-venous malformation, minimum size detected by the isocount method was 2 cm in diameter. To twenty one cases of the cerebral infarction, total thirty two scanning examinations were performed, including postictal follow up studies. It is often said that it is two or three weeks after the ictus when the infarcted cerebral lesion is most clearly detectable by the scintigraphic procedures, presumably due to focal neovascularizations which may occur in the lesion most prominently at this postictal stage. Contradicted to the current concept, our experiences show that abnormal dot accumulations are recognized in the scintigrams even at the earlier stage, thus among five cases of cerebral infarction scanned within a week after the ictus positive figures were obtained in four cases, two of which were examined within two days after the ictus. Focal breakdown of blood brain barrier at the acute stage is considered to be responsible for the early positivity in cerebral infarctions. In eight cases among twenty one cerebral infarctions angiographies failed to demonstrate the vessel occluded. The isocount scanning method, however, succeeded in getting positive results in seven of the eight cases. It will be emphasized that the isocount scanning is a preferable diagnostic procedure in the cerebrovascular diseases, especially when the angiography is hesitated to be performed because of the patient severely affected.

Adolescent↗
PubMed2003

Development of cortisol circadian rhythm in infancy.

BACKGROUND AND AIMS: Cortisol is the final product of the hypothalamus-pituitary-adrenal (HPA) axis. It is secreted in a pulsatile fashion that displays a circadian rhythm. Infants are born without a circadian rhythm in cortisol and they acquire it during their first year of life. Studies do not agree on the age of appearance of the circadian rhythm (varying between 2 weeks till the age of 9 months) nor on whether it is related to the appearance of the sleep-wake circadian rhythm. The object of the present study was to find evidence of the age of appearance of the diurnal rhythm of cortisol and to compare the results obtained by several different analysis methods on a new data set. DESIGN AND MEASURES: Cortisol was determined in salival samples of 14 normally developing infants who were followed monthly between the ages of 2 and 5 months. The data were analyzed with several previously published analysis methods as well as with Multilevel Analysis (Hierarchical Linear Modeling). RESULTS: The previously published analysis methods each produced different results when applied to the current data set. Moreover, our results indicate striking differences between young infants in both age of appearance and stability of the diurnal cortisol rhythm. Also, a link was found between the appearance of the sleep-wake circadian rhythm and the cortisol circadian rhythm. An important intraindividual variability in cortisol levels was found even after correcting for the different variables that affect cortisol (i.e. time of sampling, feeding, etc.). CONCLUSIONS: Although the choice of analysis method influences the age of appearance obtained, our use of HLM shows that the infants' own variability in onset and stability of the cortisol circadian rhythm greatly contributes to the different results.

Adult↗
PubMed2006

How to begin a new topic in mathematics: does it matter to students' performance in mathematics?

The authors use Canadian data from the Third International Mathematics and Science Study to examine six instructional methods that mathematics teachers use to introduce new topics in mathematics on performance of eighth-grade students in six mathematical areas (mathematics as a whole, algebra, data analysis, fraction, geometry, and measurement). Results of multilevel analysis with students nested within schools show that the instructional methods of having the teacher explain the rules and definitions and looking at the textbook while the teacher talks about it had little instructional effects on student performance in any mathematical area. In contrast, the instructional method in which teachers try to solve an example related to the new topic was effective in promoting student performance across all mathematical areas.

Adolescent↗
PubMed2001

Diastolic blood pressure and area of residence: multilevel versus ecological analysis of social inequity.

STUDY OBJECTIVES: To study geographical differences in diastolic blood pressure and the influence of the social environment (census percentage of people with low educational achievement) on individual diastolic blood pressure level, after controlling for individual age and educational achievement. To compare the results of multilevel and ecological analyses. DESIGN: Cross sectional analysis performed by multilevel linear regression modelling, with women at the first level and urban areas at the second level, and by single level ecological regression using areas as the unit of analysis. SETTING: Malmö, Sweden (population 250 000). PARTICIPANTS: 15 569 women aged 45 to 73, residing in 17 urban areas, who took part in the Malmö Diet and Cancer Study (1991-1996). MAIN RESULTS: In the "fixed effects" multilevel analysis, low educational achievement at both individual (beta=1.093, SE=0.167) and area levels (beta=2.966, SE=1.250) were independently associated with blood pressure, although in the "random effects" multilevel analysis almost none of the total variability in blood pressure across persons was attributable to areas (intraclass correlation=0.3%). The ecological analysis also found an association between the area educational variable and mean diastolic blood pressure (beta=4.058, SE=1.345). CONCLUSIONS: The small intraclass correlation found indicated very marginal geographical differences and almost no influence of the urban area on individual blood pressure. However, these slight differences were enough to detect an effect of the social environment on blood pressure. The ecological study overestimated the associations found in the "fixed" effects multilevel analysis, and neither distinguished individual from area levels nor provided information on the intraclass correlation. Ecological analyses are inadequate to evaluate geographical differences in health.

Age Factors↗
PubMed1991

Multilevel modelling of longitudinal cephalometric data explained for orthodontists.

Multilevel modelling of longitudinal data is an important new statistical technique. In this article some of the basic concepts and ideas of multilevel modelling are explained. The model is introduced by showing how individual and average growth can be modelled. The intercept, linear and quadratic coefficient, between and within variance, fixed and random part, and other concepts of multilevel modelling are explained. Attention is also given to the reading of statistical tables of the results of multilevel analysis. In the conclusion some of the advantages of multilevel modelling of cephalometric data are mentioned.

Aging↗
PubMed1996

The design and analysis of social-interaction research.

Static models of interacting persons measured at the interval level are reviewed. A discussion of the fundamental sources of variance and key design decisions in social-interaction research is presented. Outlined are the basic designs for social-interaction research and their proper analysis. Multilevel modeling is likely to become the most common data analysis method. Critical issues unique to social-interaction research are examined, particularly the effect of the partner on the interaction actor. Finally, illustrations of analyses from four extended examples are presented.

Adult↗
PubMed2001

A hierarchical analysis of long-term illness and mortality in socially deprived areas.

This article is a multilevel analysis of the effects on self-reported long-term illness and mortality of the socio-economic position of the neighbourhood. Using data from the Swedish Level of Living Survey, neighbourhood social position is measured by a composite Care Need Index, (CNI) together with such indicators of individual socio-economic position as occupation and housing tenure, with adjustment for age, sex, marital status and social network. Data came from 22,236 people aged 25-74, and were collected from 1988 to 1992. The cross-sectional data were analysed using a hierarchical logistic regression model. In a second analysis, each participant was followed from the initial interview until his or her death, or until the termination of data collection (31 December 1996). A neighbourhood's low social position and an individual resident's low socio-economic position (i.e., a manual worker, or person renting a flat) were found to be associated with increased risk of long-term illness. We conclude that a neighbourhood's low socio-economic position, that is, a high score on the CNI, is a risk factor for long-standing illness above and beyond an individual's socio-economic position. The differences in mortality could be explained by the included independent individual variables.

Adult↗
PubMed2006

Risk factors for local progression after percutaneous radiofrequency ablation of lung tumors: evaluation based on a preliminary review of 342 tumors.

BACKGROUND: The purpose of the study was to retrospectively evaluate the risk factors for local progression after percutaneous radiofrequency (RF) ablation of lung tumors. METHODS: The study included 128 patients (77 men, 51 women; mean age, 61.3 years) with 342 tumors (25 primary and 317 metastatic lung neoplasms; mean long-axis diameter, 1.7 cm) treated with RF ablation. The overall primary and secondary technique effectiveness rates were estimated using Kaplan-Meier analysis. Multiple variables were analyzed using the log-rank test, followed by multivariate multilevel analysis to determine independent risk factors for local progression. The primary and secondary technique effectiveness rates were again estimated when considering only tumors without independent risk factors. RESULTS: The median follow-up period was 12 months (range, 6-47 months). The overall primary and secondary technique effectiveness rates were 72% and 84% at 1 year, 60% and 71% at 2 years, and 58% and 66% at 3 years, respectively. Larger tumor size (hazard ratio [HR], 1.97; 95% confidence interval [95% CI], 1.47-2.65; P < .00001) and the use of an internally cooled electrode (HR, 2.32; 95% CI, 1.10-4.90; P = .027) were assessed as independent risk factors for local progression. The primary and secondary technique effectiveness rates when considering tumors smaller than 2 cm and treated with a multitined expandable electrode were 89% and 89% at 1 year and 66% and 78% at 2 years, respectively. CONCLUSIONS: Larger tumor size and the use of an internally cooled electrode were independent risk factors for local progression after RF ablation of lung tumors.

Adult↗
PubMed2005

Exposure to inorganic arsenic in drinking water and total urinary arsenic concentration in a Chilean population.

The relationship of inorganic arsenic exposure through drinking water and total urinary arsenic excretion in a nonoccupationally exposed population was evaluated in a cross-sectional study in three mayor cities of Chile (Antofagasta, Santiago, and Temuco). A total of 756 individuals in three population strata (elderly, students, and workers) provided first morning void urine specimens the day after exposure and food surveys were administered. Arsenic intake from drinking water was estimated from analysis of tap water samples, plus 24-h dietary recall and food frequency questionnaires. Multilevel analysis was used to evaluate the effects of the age group and city factors adjusted by predictor variables. Arsenic levels in drinking water and urine were significantly higher in Antofagasta compared with the other cities. City-and individual-level factors, 12% and 88%, respectively, accounted for the variability in urinary arsenic concentration. The main predictors of urinary arsenic concentration were total arsenic consumption through water and age. These findings indicate that arsenic concentration in drinking water continues to be the principal contributing factor to exposure to inorganic arsenic in the Chilean population.

Adolescent↗
PubMed2003

Unification of the "burst" and "linear" theories of periodontal disease progression: a multilevel manifestation of the same phenomenon.

Previously, burst and linear theories for periodontal disease progression were proposed based on different but limited statistical methods of analysis. Multilevel modeling provides a new approach, yielding a more comprehensive model. Random coefficient models were used to analyze longitudinal periodontal data consisting of repeated measures (level 1), sites (level 2), teeth (level 3), and subjects (level 4). Large negative and highly significant correlations between random linear and quadratic time coefficients indicated that subjects and teeth with greater-than-average linear change experienced decelerated variation. Conversely, subjects and teeth with less-than-average linear change experienced accelerated variation. Change therefore exhibited a dynamic regression to the mean at the tooth and subject levels. Since no equilibrium was attained throughout the study, changes were cyclical. When considered as a multilevel system, the "linear" and "burst" theories of periodontal disease progression are a manifestation of the same phenomenon: Some sites improve while others progress, in a cyclical manner.

Adolescent↗
PubMed2006

Has patients' involvement in the decision-making process changed over time?

OBJECTIVE: To get insight into the changes over time of patients' involvement in the decision-making process, and into the factors contributing to patients' involvement and general practitioners' (GPs) communication related to the Medical Treatment Act (MTA) issues: information about treatment, other available treatments and side-effects; informed decision making; asking consent for treatment. BACKGROUND: Societal developments have changed the doctor-patient relationship recently. Informed decision making has become a central topic. Patients' informed consent was legalized by the MTA (1995). DESIGN: Data of two cross-sectional studies, the First (1987) and Second (2001) Dutch National Survey of General Practice, were compared. SETTING AND PARTICIPANTS: General practice consultations; 16 GPs and 442 patients in 1987; 142 GPs and 2784 patients in 2001. METHODS: Consultations were videotaped and rated using Roter's Interaction Analysis System and observer questionnaires; pre- and post-consultation patient questionnaires; and GP questionnaires. Descriptive analyses and multivariate, multilevel analysis were applied. MAIN RESULTS: Most patients reported to have received the information they had considered as important prior to the consultation. There were discrepancies in involvement in treatment decisions and in giving information about other available treatments, side-effects and risks. GPs who were more affective and gave more information, more often involved their patients, especially younger patients, in decision making. In 2001, more informed decision making was observed and the GPs asked consent for a treatment more often, but they less often asked for the patients' understanding. CONCLUSION: Patients' involvement in decision making has increased over time, but not in every respect. However, this does not apply for all patients, especially the older ones. It should be questioned whether they are willing or capable to be involved and if so, how they could be encouraged.

Adult↗
PubMed1995

Maternal HIV infection, drug use, and growth of uninfected children in their first 3 years.

OBJECTIVE: To determine the separate effects of maternal HIV infection and drug use during pregnancy on growth of uninfected children in their first 3 years. DESIGN: Retrospective analysis of measurements from health visitor records made during routine child health surveillance at 6 weeks, 10 months, and 3 years of age. Multilevel analysis allowed for between-infant variation in fitted growth lines, and adjustment for other factors. Growth was described in terms of an intercept (z score at term) and growth slopes (change in z score per year) up to, and from, 4 months. SUBJECTS: 290 case babies delivered in Edinburgh hospitals to women who reported injection drug use by either themselves or their HIV infected partner, and 186 community controls. A total of 131 (45%) of the case babies were born to women who used drugs, predominantly opiates, during pregnancy and 93 (32%) to HIV infected women. The eight infected children were excluded from analysis. MAIN OUTCOME MEASURES: Age and sex standardised z scores for height, weight, and body mass index. RESULTS: 459 (96%) of the 476 records for cases and controls were traced, yielding 1432 weight and 939 height measurements. Maternal HIV infection was not found to affect growth; at 3 years the estimated effect on weight z score was 0.16 with 95% confidence interval (-0.25 to 0.57) and for height 0.18 (-0.19 to 0.55). Drug use during pregnancy was associated with lighter babies at 40 weeks followed by depressed growth in the first four months, these infants remaining just slightly smaller at 3 years with an estimated effect on z scores of -0.5 for weight with 95% confidence interval (-0.89 to -0.11) and -0.37 (-0.72 to -0.02) for height. CONCLUSIONS: Maternal HIV infection does not adversely affect growth in uninfected infants, and the effect of drug use during pregnancy is limited to small decrease in size at 3 years.

Body Height↗
PubMed2006

An examination of the dynamic relationship between self-efficacy and performance across levels of analysis and levels of specificity.

This research used resource allocation theory to generate predictions regarding dynamic relationships between self-efficacy and task performance from 2 levels of analysis and specificity. Participants were given multiple trials of practice on an air traffic control task. Measures of task-specific self-efficacy and performance were taken at repeated intervals. The authors used multilevel analysis to demonstrate differential and dynamic effects. As predicted, task-specific self-efficacy was negatively associated with task performance at the within-person level. On the other hand, average levels of task-specific self-efficacy were positively related to performance at the between-persons level and mediated the effect of general self-efficacy. The key findings from this research relate to dynamic effects--these results show that self-efficacy effects can change over time, but it depends on the level of analysis and specificity at which self-efficacy is conceptualized. These novel findings emphasize the importance of conceptualizing self-efficacy within a multilevel and multispecificity framework and make a significant contribution to understanding the way this construct relates to task performance.

Adult↗
PubMed2005

Statistical analysis of data in support of the Barker hypothesis, advantages of using random effects regression model in hierarchical data.

In a recent note by Walters and Edwards (2004), the authors argued that summary statistics should be used in analysing hierarchical data from our earlier analysis of a rat model of developmental programming and the Barker hypothesis (Kwong et al., 2000, 2004). We reiterate here why such a view is inappropriate. Hierarchical data merits multilevel analysis using a 'random effects' model to enable estimation of variances at different levels and easy assessment of other parameters in a complex data structure.

Analysis of Variance↗
PubMed2006

Multilevel modelling of the incidence of visceral leishmaniasis in Teresina, Brazil.

Epidemics of visceral leishmaniasis (VL) in major Brazilian cities are new phenomena since 1980. As determinants of transmission in urban settings probably operate at different geographic scales, and information is not available for each scale, a multilevel approach was used to examine the effect of canine infection and environmental and socio-economic factors on the spatial variability of incidence rates of VL in the city of Teresina. Details on an outbreak of greater than 1200 cases of VL in Teresina during 1993-1996 were available at two hierarchical levels: census tracts (socio-economic characteristics, incidence rates of human VL) and districts, which encompass census tracts (prevalence of canine infection). Remotely sensed data obtained by satellite generated environmental information at both levels. Data from census tracts and districts were analysed simultaneously by multilevel modelling. Poor socio-economic conditions and increased vegetation were associated with a high incidence of human VL. Increasing prevalence of canine infection also predicted a high incidence of human VL, as did high prevalence of canine infection before and during the epidemic. Poor socio-economic conditions had an amplifying effect on the association between canine infection and the incidence of human VL. Focusing interventions on areas with characteristics identified by multilevel analysis could be a cost-effective strategy for controlling VL. Because risk factors for infectious diseases operate simultaneously at several levels and ecological data usually are available at different geographical scales, multilevel modelling is a valuable tool for epidemiological investigation of disease transmission.

Animals↗
PubMed1998

Gender and communication style in general practice. Differences between women's health care and regular health care.

OBJECTIVES: Differences were investigated between general practitioners providing women's health care (4 women) and general practitioners providing regular health care (8 women and 8 men). Expectations were formulated on the basis of the principles of women's health care and literature about gender differences. METHODS: Data were used from 405 videotaped consultations of female patients (over 15 years). Roter's Interaction Analysis System (RIAS) was used to measure the verbal affective and instrumental behavior of the doctors and their patients. These data were supplemented by various nonverbal measures. The data were analyzed by means of multilevel analysis. RESULTS: Doctors in the women's health care practice (called Aletta) look at their patients and talk with them more than other doctors. The general practitioners have approximately the same affective behavior, but the Aletta doctors show more verbal attentiveness and warmth. They also give more medical information and advice. Most of the characteristics of Aletta doctors fit female doctors providing regular health care too. Male doctors show a less communicative behavior in most respects. The differences between general practitioners are reflected in their patients' communication style. CONCLUSIONS: The integration into regular care of some aspects of doctor-patient communication that were found in women's health care might be desirable in the light of the further improvement of the quality of care for women and men.

Affect↗