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PubMed2002

Corpectomy versus laminoplasty for multilevel cervical myelopathy: an independent matched-cohort analysis.

STUDY DESIGN: Matched patient cohorts using retrospective chart and radiographic review with independent clinical and radiographic follow-up were reviewed. OBJECTIVE: To compare the clinical and radiographic outcomes of multilevel corpectomy and laminoplasty using an independent matched-cohort analysis. SUMMARY OF BACKGROUND DATA: The treatment of choice for multilevel cervical myelopathy remains a matter of investigation. For the decompression of three or more motion segments, multilevel corpectomy and laminoplasty have proven effective while avoiding the pitfalls of laminectomy. Direct clinical comparisons of these two procedures are few in number and are limited by the heterogeneity in their patient groups. METHODS: Medical records of all patients treated for multilevel cervical myelopathy with either multilevel corpectomy or laminoplasty between 1994 and 1999 at the Emory Spine Center were reviewed. From a pool of 38 patients meeting stringent inclusion and exclusion criteria, 13 patients who underwent multilevel corpectomy were blindly matched with 13 patients who underwent laminoplasty based on known prognostic criteria. A single physician independently evaluated each patient and their radiographs at their latest follow-up appointment. RESULTS: The cohorts were well matched by age, duration of symptoms, severity of myelopathy (Nurick grade), and preoperative sagittal alignment (C2-C7). Mean operative time, blood loss, and hospital stay were nearly identical. The mean follow-up for multilevel corpectomy and laminoplasty were 49 and 40 months, respectively. Improvement in function averaged 1.6 Nurick grades after laminoplasty and 0.9 grades after multilevel corpectomy (P > 0.05). Subjective improvements in strength, dexterity, sensation, pain, and gait were similar for the two operations. The prevalence of axial discomfort at the latest follow-up was the same for each cohort, but the analgesic requirements tended to be greater for patients who underwent multilevel corpectomy. Sagittal motion from C2 to C7 decreased by 57% after multilevel corpectomy and by 38% after laminoplasty. One complication (C6-C7 herniated nucleus pulposus [HNP] requiring anterior discetomy with fusion) occurred in the laminoplasty group. Multilevel corpectomy complications included progression of myelopathy, nonunion, persistent dysphagia, persistent dysphonia, and subjacent motion segment ankylosis. CONCLUSIONS: Both multilevel corpectomy and laminoplasty reliably arrest myelopathic progression in multilevel cervical myelopathy and can lead to significant neurologic recovery and pain reduction in a majority of patients. Surprisingly, the laminoplasty cohort tended to require less pain medication at final follow-up than did the multilevel corpectomy cohort. Given this and the higher prevalence of complications among multilevel corpectomy patients, it is believed that laminoplasty may be the preferred method of treatment for multilevel cervical myelopathy in the absence of preoperative kyphosis.

Adult↗
PubMed1996

Effect of physician profiling on utilization. Meta-analysis of randomized clinical trials.

OBJECTIVES: An American Medical Association survey reported that more than half of physicians are subjects of either clinical or economic profiling. This multilevel meta-analysis was designed to assess the clinical effect of peer-comparison feedback intervention (profiles) in changing practice patterns. METHODS: Systematic computerized and manual searches were combined to retrieve articles on randomized controlled clinical trials testing profiling reports. Eligible studies were randomized, controlled clinical trials that tested peer-comparison feedback intervention and measured utilization of clinical procedures. To use all available information, data were abstracted and analyzed on three levels: (1) direction of effects, (2) p value fro the statistical comparison, and (3) odds ratio (OR). MAIN RESULTS: In the 12 eligible trials, 553 physicians were profiled. The test result was p < .05 for the vote-counting sign test of 12 studies (level 1) and p < .05 for the z-transformation test of 8 studies (level 2). There were 5 trials included in the OR analysis (level 3). The primary effect variable in two of the 5 trials had a nonsignificant OR. However, the overall OR calculated by the Mantel-Haenszel method was significant (1.091, confidence interval: 1.045 to 1.136). CONCLUSIONS: Profiling has a statistically significant, but minimal effect on the utilization of clinical procedures. The results of this study indicate a need for controlled clinical evaluations before subjecting large numbers of physicians to utilization management interventions.

Confidence Intervals↗
PubMed2002

Smoking in young adolescents: an approach with multilevel discrete choice models.

STUDY OBJECTIVE: To understand the context for tobacco smoking in young adolescents, estimating the effects of individual, family, social, and school related factors. DESIGN: Cross sectional analysis performed by multilevel logistic regression with pupils at the first level and schools at the second level. The data came from a stratified sample of students surveyed on their own, their families' and their friends' smoking habits, their schools, and their awareness of cigarette prices and advertising. SETTING: The study was performed in the Island of Gran Canaria, Spain. PARTICIPANTS: 1877 students from 30 secondary schools in spring of 2000 (model's effective sample sizes 1697 and 1738). MAIN RESULTS: 14.2% of the young teenagers surveyed use tobacco, almost half of them (6.3% of the total surveyed) on a daily basis. According to the ordered logistic regression model, to have a smoker as the best friend increases significantly the probability of smoking (odds ratio: 6.96, 95% confidence intervals (CI) (4.93 to 9.84), and the same stands for one smoker living at home compared with a smoking free home (odds ratio: 2.03, 95% CI 1.22 to 3.36). Girls smoke more (odds ratio: 1.85, 95% CI 1.33 to 2.59). Experience with alcohol, and lack of interest in studies are also significant factors affecting smoking. Multilevel models of logistic regression showed that factors related to the school affect the smoking behaviour of young teenagers. More specifically, whether a school complies with antismoking rules or not is the main factor to predict smoking prevalence in schools. The remainder of the differences can be attributed to individual and family characteristics, tobacco consumption by parents or other close relatives, and peer group. CONCLUSIONS: A great deal of the individual differences in smoking are explained by factors at the school level, therefore the context is very relevant in this case. The most relevant predictors for smoking in young adolescents include some factors related to the schools they attend. One variable stood out in accounting for the school to school differences: how well they enforced the no smoking rule. Therefore we can prevent or delay tobacco smoking in adolescents not only by publicising health risks, but also by better enforcing no smoking rules in schools.

Adolescent↗
PubMedDate not supplied

Kin influence on female reproductive behavior: the evidence from reconstitution of the Bejsce parish registers, 18th to 20th centuries, Poland.

The phenomenon of kin-oriented help, according to inclusive fitness theory, should be of crucial importance with respect to the process of reproduction. This is due to the fact that the devoted time and resources might indirectly contribute to the reproductive performance of a donor. This study aimed at analyzing the kin effects on fertility in order to check whether help received from kinsmen enhance a recipient's reproduction in terms of parity transition risk, completed fertility, and the number of survivors. The data came from reconstitution of church registers from Bejsce parish, Poland. To estimate the kin effect, regression models for count outcomes and techniques of multilevel event history analysis were applied. The analyses have shown that completed fertility and parity-specific transition risks are strongly influenced by various kin groups. Moreover, a multilevel hazard model revealed differences in the patterns of the kin influence among controlled fertility than among natural fertility birth cohorts. Female reproductive outcome is influenced mainly by the presence of siblings and postreproductive helpers (grandparents). However, there is a negative impact of so-called helpers-at-the-nest (older children in the household) on parity transition risks.

Cohort Studies↗
PubMed1996

The effect of human immunodeficiency virus infection and drug use on birth characteristics.

OBJECTIVE: To explore the effect of human immunodeficiency virus (HIV) infection and drug use on birth weight, length, and gestational duration at delivery. METHODS: Subjects had a history of injection drug use or a sexual partner who was an injection drug user, were Scottish, and their HIV serostatus during pregnancy was known. Control pregnancies were matched for age, parity, ethnic group, year of delivery, and postal code sector of home address. In addition, some were matched for smoking and housing deprivation score. Birth weights were standardized for gestational age by expressing them as z scores with a mean of zero and a standard deviation of unity. Statistical analysis was by univariate and multiple regression with multilevel modeling. RESULTS: Regression analysis for birth weight, gestational age, and gestation-adjusted birth weights (z score) included 789 pregnancies in 693 women. Human immunodeficiency virus seropositivity was associated with a z score that was 0.27 lower (P = .03), but there was no significant difference in gestational duration at delivery. Current oral or injection drug use were associated with a reduction in standardized birth weight (z score -0.27, P = .06, and z score -0.28, P = .04, respectively), and injection drug use with a reduction in occipitofrontal circumference only (1.8 cm reduction, P = .05). Injection drug use, but not the other factors, had an effect on gestational age at delivery (1.54 weeks earlier, P < .001). CONCLUSION: Although HIV seropositivity is associated with a small reduction in standardized birth weight, this effect is less than that attributable to smoking and may not be of clinical significance. The effect seems to be associated with placental size. Opiate use, regardless of route, had a small association with reduced birth weight, suggesting a specific drug effect. However, only injection drug use had a strong association with early delivery, and this effect was likely to be clinically significant at the population level.

Birth Weight↗
PubMed2001

Efficiency analysis of diffractive lenses.

Multilevel diffractive optical elements are necessary for achieving high-efficiency performance. Here the diffraction efficiency of a multilevel phase-only diffractive lens is analyzed. Approximate, as well as more accurate, approaches are presented. Both plane-wave and Gaussian illumination are discussed. It is shown that for many practical cases the diffraction efficiency can be determined by only a single parameter that takes into account the spatial bandwidth product as well as the focal length of the lens and the illumination wavelength. The analysis is based on the scalar theory and the thin-element approximation. Justification for doing this is presented. The results are valid for lenses with at least F/5.

Journal Article↗
PubMed2006

Centering or not centering in multilevel models? The role of the group mean and the assessment of group effects.

In multilevel regression, centering the model variables produces effects that are different and sometimes unexpected compared with those in traditional regression analysis. In this article, the main contributions in terms of meaning, assumptions, and effects underlying a multilevel centering solution are reviewed, emphasizing advantages and critiques of this approach. In addition, in the spirit of Manski, contextual and correlated effects in a multilevel framework are defined to detect group effects. It is shown that the decision of centering in a multilevel analysis depends on the way the variables are centered, on whether the model has been specified with or without cross-level terms and group means, and on the purposes of the specific analysis.

Evaluation Studies as Topic↗
PubMed2006

Marginal modeling of nonnested multilevel data using standard software.

Epidemiologic data are often clustered within multiple levels that may not be nested within each other. Generalized estimating equations are commonly used to adjust for correlation among observations within clusters when fitting regression models; however, standard software does not currently accommodate nonnested clusters. This paper introduces a simple generalized estimating equation strategy that uses available commercial or public software for the regression analysis of nonnested multilevel data. The authors describe how to obtain empirical standard error estimates for constructing valid confidence intervals and conducting statistical hypothesis tests. The method is evaluated using simulations and illustrated with an analysis of data from the Breast Cancer Surveillance Consortium that estimates the influence of woman, radiologist, and facility characteristics on the positive predictive value of screening mammography. Performance with a small number of clusters is discussed. Both the simulations and the example demonstrate the importance of accounting for the correlation within all levels of clustering for proper inference.

Adult↗
PubMed1993

[Aortofemoral bypass and extensive profunda-plasty in combined arterial occlusive disease of the pelvic-femoral type--a stage oriented analysis].

121 patients with multilevel, lower extremity arterial occlusive disease were treated by aortofemoral reconstruction and extended profundoplasty. Early and late results of 201 limbs were analyzed according to their preoperative grade of ischemia. In the case of moderate claudication the success rate was 43% postoperatively and 81% after 5 years. When having severe claudication the success rate was 62% and 79% after 5 years. The revascularisation of the deep femoral artery helps developing the collateral arteries, responsible for an improvement after a considerable period of time. In limbs with rest pain we got a success rate of 78% postoperatively and 76% after 5 years. In the case of gangrene the primary success rate was 40% and 68% after 5 years. Angiographically, severe arteriosclerotic lesions were documented in the deep femoral artery and popliteal artery when limb-threatening ischemia was present. Nevertheless, the combined aortofemoral and extended deep femoral artery reconstruction was efficient in treating the multilevel occlusive disease; subsequent femoro-distal bypass was necessary only in case of threatening ischemia for 9.3% of limbs. Our findings show there is no indication for simultaneous aortofemoral and femoro-distal bypass grafting in the treatment of the multilevel disease.

Aorta, Abdominal↗
PubMed2006

C-reactive protein and angiographic characteristics of stable and unstable coronary artery disease: data from the prospective PREVEND cohort.

AIMS: High sensitive-C-reactive protein (hs-CRP) is associated with coronary risk, which may be explained by an association with (unstable) coronary artery disease (CAD). Until now, histopathological and angiographic studies have failed to consistently demonstrate a strong relationship. However, most of these studies were limited by a cross-sectional design. Our aim was to prospectively evaluate the association between hs-CRP and plaque instability. Therefore, firstly, we investigated the relation between hs-CRP measured long before coronary angiography (CAG) and angiographic characteristics of stable and unstable CAD. In addition, we investigated the association with coronary events during follow up in the total PREVEND population. METHODS AND RESULTS: Of the population based Prevention of Renal and Vascular Endstage Disease (PREVEND) study, 8139 subjects without previous documented CAD were followed for the incidence of CAG and coronary events from 1997 to 2003. For the qualitative angiographic analysis, 216 CAGs were available. Mean time to CAG was 37+/-19 months. The 864 coronary vessels were graded as follows: 436 coronary vessels as normal, 175 as non-obstructive CAD, 179 as stable obstructive CAD and 74 as unstable obstructive CAD. Multilevel ordinal regression analysis was performed to study associations between baseline clinical variables and angiographic findings. Hs-CRP contributed significantly to the multivariate model after adjustment for age, gender, smoking, lipids and blood pressure. In 8139 subjects, 201 (2.5%) first coronary events occurred during follow up. Cox survival analysis showed age- and sex-adjusted hazard ratios for hs-CRP 1-3 and >3mg/L of, respectively, 1.26 (95% CI 0.67-2.40) and 3.16 (95% CI 1.26-3.16), relative to hs-CRP <1mg/L. CONCLUSION: In the prospective PREVEND study of subjects without previous documented CAD, hs-CRP levels at baseline were associated with angiographic characteristics and clinical consequences of plaque instability during follow up. This observation supports the concept that hs-CRP significantly contributes to coronary atherogenesis.

Aged↗
PubMed2006

Neighborhood social capital and dental injuries in Brazilian adolescents.

OBJECTIVES: Evidence suggests that communities with higher levels of social capital have better health, but this association has not been explored specifically in relation to dental injury. We investigated the association between social capital and dental injury. METHODS: We conducted a multilevel study assessed individual and neighborhood effects on dental injury of 1302 14- to 15-year-old adolescents in 39 schools of Distrito Federal, Brazil. Children underwent a dental examination and, with their parents, answered a questionnaire about their local environments. Our data analysis used logistic multilevel modeling of students and neighborhood (the latter defined by catchment areas of schools). RESULTS: The prevalence of dental injury was significantly lower in neighborhoods with higher levels of social capital, especially among boys. After control for individual and neighborhood variables, the adjusted odds ratio for a 1-unit increase in the standardized social capital index was 0.55 (95% confidence interval=0.37, 0.81; P=.002) among boys. CONCLUSIONS: Social capital may explain inequalities in rates of dental injury, especially among boys.

Adolescent↗
PubMed2006

The potential impact of neighborhood empowerment on dental caries among adolescents.

OBJECTIVE: Empowerment has been considered a dimension of social capital. It refers to social interaction processes that enable people to enhance their individual and collective skills and to exert greater control over their lives. This relationship has not been explored in relation to dental health. The objective of this study was to investigate the association between neighborhood empowerment and dental caries in adolescents. METHODS: A multilevel study was designed to assess the individual and neighborhood effects on the oral health of adolescents. Four sources of data were used: (a) clinical examinations (WHO), (b) students' questionnaires, (c) parents' questionnaires and (d) census data. The study population was 1302, 14/15-year-old students from 39 public schools of two cities of the Distrito Federal (DF), Brazil. Data analysis used logistic multilevel modeling at two levels: students (sources a and b) and neighborhood as defined by catchment areas of schools (sources c and d). RESULTS: High DMFT (DMFT > median, DMFT > or =3) rates were significantly lower in areas with higher levels of empowerment. This relationship was independent of socioeconomic variables at the individual and area levels and of all other individual risk factor variables such as sex, fluoride, sugar consumption, tooth brushing and dental attendance [OR for low compared with high empowerment was 1.54 (95% CI = 1.09-2.18), P = 0.014]. CONCLUSIONS: Neighborhood empowerment may play an important role in explaining inequalities in the levels of dental caries. New perspectives are needed so that more effective interventions can be implemented using area-based perspectives.

Adolescent↗
PubMed2006

Modeling crash outcome probabilities at rural intersections: application of hierarchical binomial logistic models.

It is important to examine the nature of the relationships between roadway, environmental, and traffic factors and motor vehicle crashes, with the aim to improve the collective understanding of causal mechanisms involved in crashes and to better predict their occurrence. Statistical models of motor vehicle crashes are one path of inquiry often used to gain these initial insights. Recent efforts have focused on the estimation of negative binomial and Poisson regression models (and related deviants) due to their relatively good fit to crash data. Of course analysts constantly seek methods that offer greater consistency with the data generating mechanism (motor vehicle crashes in this case), provide better statistical fit, and provide insight into data structure that was previously unavailable. One such opportunity exists with some types of crash data, in particular crash-level data that are collected across roadway segments, intersections, etc. It is argued in this paper that some crash data possess hierarchical structure that has not routinely been exploited. This paper describes the application of binomial multilevel models of crash types using 548 motor vehicle crashes collected from 91 two-lane rural intersections in the state of Georgia. Crash prediction models are estimated for angle, rear-end, and sideswipe (both same direction and opposite direction) crashes. The contributions of the paper are the realization of hierarchical data structure and the application of a theoretically appealing and suitable analysis approach for multilevel data, yielding insights into intersection-related crashes by crash type.

Accidents, Traffic↗
PubMed2005

[More social exclusion of chronically ill patients with lower incomes].

OBJECTIVE: To determine whether income is connected with the variation in the social exclusion of chronically ill patients. DESIGN: Descriptive. METHOD: In 223 chronically ill patients that had been detected via patients' associations, general practitioners and outpatient clinics, a structured interview was administered during a home visit 4 times during a period of 7 months (October 2003-April 2004). Due to dropouts, the actual number of patients interviewed at each of the 4 times was 223, 176, 143 and 105, respectively. Social exclusion was measured with the aid of the 'Autonomy outside the home' subscale of the 'Impact on participation and autonomy' questionnaire. The possible total score varied from 5 (little social exclusion) to 25 (much social exclusion). In order to explain a possible effect of income, various other patient characteristics were added to the analysis model: type of primary disease (rheumatism, multiple sclerosis, pulmonary emphysema, other), duration of the primary disease, comorbidity, educational level, whether or not the patient was employed or engaged in volunteer work, whether or not the patient lived together with a partner, the self-rated health, physical functioning, social functioning, mental functioning, and the subjective pain. The data were analysed by means of multilevel repeated regression analysis. RESULTS: A low income was associated with social exclusion at all 4 times of measurement. The regression coefficient of income was -1.47 (95% CI: -2.28- -0.65), indicating that the score on the scale for social exclusion decreased by 1.47 for every euro 544,- (= 1 x SD) increase in net monthly income. This relationship could not be explained by the other patient characteristics, not even by a low educational level. CONCLUSION: The supportive care intended for the prevention of social exclusion of chronically ill patients should be concentrated sufficiently on those who have too little income to organise such care for themselves.

Adolescent↗
PubMed2003

Early reconstruction failures after multilevel cervical corpectomy.

STUDY DESIGN: A retrospective analysis of graft and plate complications after multilevel anterior cervical corpectomy and fusion (ACF) attributed to spondylosis, stenosis, and ossification of posterior longitudinal ligament was conducted. OBJECTIVE: To identify factors contributing to graft and plate complications in this population. SUMMARY OF BACKGROUND DATA: Biomechanical factors contributing to the increased morbidity associated with plated multilevel ACF were evaluated. METHODS: Graft- and/or plate-related complications were retrospectively reviewed in 33 patients undergoing two-level ACF reconstructions and in seven patients having three-level ACF reconstructions performed with iliac crest grafting and instrumentation with a fixed-plated design (cervical spine locking plate). Neurologic status was assessed before surgery and after surgery using both the Nurick Grading Scale and modified JOA (Japanese Orthopaedic Association) Score. The patients were observed an average of 31.4 months after surgery. The follow-up included lateral flexion and extension radiographs and a neurologic examination. RESULTS: Two of the 33 patients undergoing two-level fusions available for long-term follow-up after surgery developed reconstruction failures. All of the remaining fusions were successful, demonstrated by lateral flexion and extension radiographs. Seven patients had plated three-level corpectomy reconstructions. Five of the seven who had anterior-only reconstruction failed. DISCUSSION: A two-level ACF reconstruction is reliable with an anterior strut graft and fixed screw plate construct. A three-level ACF reconstruction is not reliably achieved with an anterior-only construct. The construct failures may be attributed in part to the fixed-plated design being used, as well as the long lever arm of the construct. CONCLUSION: There is a 6% failure rate after fixed-plated (cervical spine locking plate) two-level ACF reconstruction but a 71% failure rate after three-level fixed-plated ACF reconstruction. Future consideration should be given to simultaneous posterior fusion.

Bone Plates↗
PubMed2005

Explained variation in a model of therapeutic decision making is partitioned across patient, physician, and clinic factors.

BACKGROUND AND OBJECTIVE: Data on therapeutic decision making have a multilevel structure that can include patient-, provider-, and facility-level variables. A statistical method is presented for attributing explained variation in patient care to different levels of aggregation in a multilevel model with the aim of prioritizing and targeting quality improvement interventions. STUDY DESIGN AND SETTING: The proposed method is used in an analysis of adherence to evidence-based guidelines for the care of patients at risk of osteoporosis. Explained variation from a multilevel model of appropriate care is partitioned across patient-, physician-, and clinic-level factors. RESULTS: The combination of patient, physician, and clinic factors explained 20.0% of the variation in patient care. Individual physician effects explained 14.0% of the variation in the data; however, more than half of this explained variation could have been attributed to the individual clinic effect. Patient fixed effects alone explained 13.4% of the variation in the observed clinical decisions. CONCLUSION: The proposed approach is an intuitive and statistically valid method for attributing explained variation in a multilevel analysis of therapeutic decision making.

Administration, Oral↗
PubMed2004

A meta-analysis of trials of transurethral needle ablation for treating symptomatic benign prostatic hyperplasia.

OBJECTIVES: To investigate the short- and long-term effectiveness of transurethral needle ablation (TUNA) of the prostate for clinical benign prostatic hyperplasia (BPH), using a meta-analysis of all clinical studies involving TUNA. METHODS: Data were extracted from two randomized trials, two non-randomized observational protocols and 10 single-arm studies conducted on TUNA, according to a determined protocol. The meta-analysis was based on the change in the mean score at the end of study from that at baseline. The estimation of the effects from the meta-analysis used a multilevel model including random effects for the studies. RESULTS: In all studies the patients recruited had severe lower urinary tract symptoms and a mean International Prostate Symptom Score (IPSS) of > 20 before treatment. The effect of TUNA was to halve the mean IPSS at 1 year after treatment and, although there was a slight tendency for the IPSS to increase in all arms from year 1 to year 5, this decrease by half was maintained at 5 years. The maximum urinary flow rate (Q(max)) also increased by approximately 70% from baseline to 1 year and in virtually all studies the mean Q(max) approached or exceeded 15 mL/s. Although there was a tendency for Q(max) to decline slightly over time, the mean Q(max) 5 years after treatment was > 50% over baseline. CONCLUSIONS: This meta-analysis shows that TUNA is an effective and minimally invasive treatment for men with clinical BPH, even when the symptoms are severe. There is a significant improvement in symptoms and flow rate after 1 year which persists for at least 5 years. TUNA therapy would appear to be an alternative to surgery and an attractive option for men who do not wish to undergo long-term medical therapy, are poor candidates for surgery or are concerned about the side-effects of TURP.

Aged↗