875 resultados para Multilevel thresholding
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This paper analyzes the development of environmental concern by using the three waves of the environmental modules of the International Social Survey Programme (ISSP). First, we discuss the measurement of environmental concern and construct a ranking of countries according to the new 2010 ISSP results. Second, we analyze the determinants of environmental concern by employing multilevel models that take individual as well as context effects into account. Third, we explore the impact of attitudes on environmental behavior and support of environmental policies. The results show that environmental concern is closely correlated with the wealth of nations. However, environmental concern decreased in OECD as well as non-OECD nations slightly during the last two decades. The decline was lower in countries with improving economic conditions suggesting that economic growth helps to maintain higher levels of environmental concern. Furthermore, attitudes have a stronger impact on support of environmental policies as compared to everyday environmental behavior.
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Left ventricular mass (LVM) is a strong predictor of cardiovascular disease (CVD) in adults. However, normal growth of LVM in healthy children is not well understood, and previous results on independent effects of body size and body fatness on LVM have been inconsistent. The purpose of this study was (1) to establish the normal growth curve of LVM from age 8 to age 18, and evaluate the determinants of change in LVM with age, and (2) to assess the independent effects of body size and body fatness on LVM.^ In Project HeartBeat!, 678 healthy children aged 8, 11 and 14 years at baseline were enrolled and examined at 4-monthly intervals for up to 4 years. A synthetic cohort with continuous observations from age 8 to 18 years was constructed. A total of 4608 LVM measurements was made from M-mode echocardiography. The multilevel linear model was used for analysis.^ Sex-specific trajectories of normal growth of LVM from age 8 to 18 was displayed. On average, LVM was 15 g higher in males than females. Average LVM increased linearly in males from 78 g at age 8 to 145 g at age 18. For females, the trajectory was curvilinear, nearly constant after age 14. No significant racial differences were found. After adjustment for the effects of body size and body fatness, average LVM decreased slightly from age 8 to 18, and sex differences in changes of LVM remained constant.^ The impact of body size on LVM was examined by adding to a basic LVM-sex-age model one of 9 body size indicators. The impact of body fatness was tested by further introducing into each of the 9 LVM models (with one or another of the body size indicators) one of 4 body fatness indicators, yielding 36 models with different body size and body fatness combinations. The results indicated that effects of body size on LVM can be distinguished between fat-free body mass and fat body mass, both being independent, positive predictors. The former is the stronger determinant. When a non-fat-free body size indicator is used as predictor, the estimated residual effect of body fatness on LVM becomes negative. ^
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In numerous intervention studies and education field trials, random assignment to treatment occurs in clusters rather than at the level of observation. This departure of random assignment of units may be due to logistics, political feasibility, or ecological validity. Data within the same cluster or grouping are often correlated. Application of traditional regression techniques, which assume independence between observations, to clustered data produce consistent parameter estimates. However such estimators are often inefficient as compared to methods which incorporate the clustered nature of the data into the estimation procedure (Neuhaus 1993).1 Multilevel models, also known as random effects or random components models, can be used to account for the clustering of data by estimating higher level, or group, as well as lower level, or individual variation. Designing a study, in which the unit of observation is nested within higher level groupings, requires the determination of sample sizes at each level. This study investigates the design and analysis of various sampling strategies for a 3-level repeated measures design on the parameter estimates when the outcome variable of interest follows a Poisson distribution. ^ Results study suggest that second order PQL estimation produces the least biased estimates in the 3-level multilevel Poisson model followed by first order PQL and then second and first order MQL. The MQL estimates of both fixed and random parameters are generally satisfactory when the level 2 and level 3 variation is less than 0.10. However, as the higher level error variance increases, the MQL estimates become increasingly biased. If convergence of the estimation algorithm is not obtained by PQL procedure and higher level error variance is large, the estimates may be significantly biased. In this case bias correction techniques such as bootstrapping should be considered as an alternative procedure. For larger sample sizes, those structures with 20 or more units sampled at levels with normally distributed random errors produced more stable estimates with less sampling variance than structures with an increased number of level 1 units. For small sample sizes, sampling fewer units at the level with Poisson variation produces less sampling variation, however this criterion is no longer important when sample sizes are large. ^ 1Neuhaus J (1993). “Estimation efficiency and Tests of Covariate Effects with Clustered Binary Data”. Biometrics , 49, 989–996^
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Blood cholesterol and blood pressure development in childhood and adolescence have important impact on the future adult level of cholesterol and blood pressure, and on increased risk of cardiovascular diseases. The U.S. has higher mortality rates of coronary heart diseases than Japan. A longitudinal comparison in children of risk factor development in the two countries provides more understanding about the causes of cardiovascular disease and its prevention. Such comparisons have not been reported in the past. ^ In Project HeartBeat!, 506 non-Hispanic white, 136 black and 369 Japanese children participated in the study in the U.S. and Japan from 1991 to 1995. A synthetic cohort of ages 8 to 18 years was composed by three cohorts with starting ages at 8, 11, and 14. A multilevel regression model was used for data analysis. ^ The study revealed that the Japanese children had significantly higher slopes of mean total cholesterol (TC) and high density lipoprotein (HDL) cholesterol levels than the U.S. children after adjusting for age and sex. The mean TC level of Japanese children was not significantly different from white and black children. The mean HDL level of Japanese children was significantly higher than white and black children after adjusting for age and sex. The ratio of HDL/TC in Japanese children was significantly higher than in U.S. whites, but not significantly different from the black children. The Japanese group had significantly lower mean diastolic blood pressure phase IV (DBP4) and phase V (DBP5) than the two U.S. groups. The Japanese group also showed significantly higher slopes in systolic blood pressure, DBP5 and DBP4 during the study period than both U.S. groups. The differences were independent from height and body mass index. ^ The study provided the first longitudinal comparison of blood cholesterol and blood pressure between the U.S. and Japanese children and adolescents. It revealed the dynamic process of these factors in the three ethnic groups. ^
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The use of group-randomized trials is particularly widespread in the evaluation of health care, educational, and screening strategies. Group-randomized trials represent a subset of a larger class of designs often labeled nested, hierarchical, or multilevel and are characterized by the randomization of intact social units or groups, rather than individuals. The application of random effects models to group-randomized trials requires the specification of fixed and random components of the model. The underlying assumption is usually that these random components are normally distributed. This research is intended to determine if the Type I error rate and power are affected when the assumption of normality for the random component representing the group effect is violated. ^ In this study, simulated data are used to examine the Type I error rate, power, bias and mean squared error of the estimates of the fixed effect and the observed intraclass correlation coefficient (ICC) when the random component representing the group effect possess distributions with non-normal characteristics, such as heavy tails or severe skewness. The simulated data are generated with various characteristics (e.g. number of schools per condition, number of students per school, and several within school ICCs) observed in most small, school-based, group-randomized trials. The analysis is carried out using SAS PROC MIXED, Version 6.12, with random effects specified in a random statement and restricted maximum likelihood (REML) estimation specified. The results from the non-normally distributed data are compared to the results obtained from the analysis of data with similar design characteristics but normally distributed random effects. ^ The results suggest that the violation of the normality assumption for the group component by a skewed or heavy-tailed distribution does not appear to influence the estimation of the fixed effect, Type I error, and power. Negative biases were detected when estimating the sample ICC and dramatically increased in magnitude as the true ICC increased. These biases were not as pronounced when the true ICC was within the range observed in most group-randomized trials (i.e. 0.00 to 0.05). The normally distributed group effect also resulted in bias ICC estimates when the true ICC was greater than 0.05. However, this may be a result of higher correlation within the data. ^
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In a cross-country comparison of 33 European countries, we tested whether a high degree of female representation attenuates the assumed negative impact of gender on political involvement. Our multilevel analyses show positive interactive effects of female representation: the degree to which the representation of women in a given country's national parliament was descriptively adequate was positively related to women's ratings of the importance of politics and self-reported political interest. With respect to political participation, the findings are mixed.
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Telecommunications have developed at an incredible speed over the last couple of decades. The decreasing size of our phones and the increasing number of ways in which we can communicate are barely the only result of this (r)evolutionary development. The latter has indeed multiple implications. The change of paradigm for telecommunications regulation, epitomised by the processes of liberalisation and reregulation, was not sufficient to answer all regulatory questions pertinent to communications. Today, after the transition from monopoly to competition, we are faced perhaps with an even harder regulatory puzzle, since we must figure out how to regulate a sector that is as dynamic and as unpredictable as electronic communications have proven to be, and as vital and fundamental to the economy and to society at large. The present book addresses the regulatory puzzle of contemporary electronic communications and suggests the outlines of a coherent model for their regulation. The search for such a model involves essentially deliberations on the question "Can competition law do it all?", since generic competition rules are largely seen as the appropriate regulatory tool for the communications domain. The latter perception has been the gist of the 2002 reform of the European Community (EC) telecommunications regime, which envisages a withdrawal of sectoral regulation, as communications markets become effectively competitive and ultimately bestows the regulation of the sector upon competition law only. The book argues that the question of whether competition law is the appropriate tool needs to be examined not in the conventional contexts of sector specific rules versus competition rules or deregulation versus regulation but in a broader governance context. Consequently, the reader is provided with an insight into the workings and specific characteristics of the communications sector as network-bound, converging, dynamic and endowed with a special societal role and function. A thorough evaluation of the regulatory objectives in the communications environment contributes further to the comprehensive picture of the communications industry. Upon this carefully prepared basis, the book analyses the communications regulatory toolkit. It explores the interplay between sectoral communications regulation, competition rules (in particular Article 82 of the EC Treaty) and the rules of the World Trade Organization (WTO) relevant to telecommunications services. The in-depth analysis of multilevel construct of EC communications law is up-to-date and takes into account important recent developments in the EC competition law in practice, in particular in the field of refusal to supply and tying, of the reform of the EC electronic communications framework and new decisions of the WTO dispute settlement body, such as notably the Mexico-Telecommunications Services Panel Report. Upon these building elements, an assessment of the regulatory potential of the EC competition rules is made. The conclusions drawn are beyond the scope of the current situation of EC electronic communications and the applicable law and explore the possible contours of an optimal regulatory framework for modern communications. The book is of particular interest to communications and antitrust law experts, as well as policy makers, government agencies, consultancies and think-tanks active in the field. Experts on other network industries (such as electricity or postal communications) can also profit from the substantial experience gathered in the communications sector as the most advanced one in terms of liberalisation and reregulation.
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Female gender and low income are two markers for groups that have been historically disadvantaged within most societies. The study explores two research questions related to their political representation: (1) ‘Are parties biased towards the ideological preferences of male and rich citizens?’; and (2) ‘Does the proportionality of the electoral system moderate the degree of under-representation of women and poor citizens in the party system?’ A multilevel analysis of survey data from 24 parliamentary democracies indicates that there is some bias against those with low income and, at a much smaller rate, women. This has systemic consequences for the quality of representation, as the preferences of the complementary groups differ. The proportionality of the electoral system influences the degree of under-representation: specifically, larger district magnitudes help in closing the considerable gap between rich and poor.
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The article offers a systematic analysis of the comparative trajectory of international democratic change. In particular, it focuses on the resulting convergence or divergence of political systems, borrowing from the literatures on institutional change and policy convergence. To this end, political-institutional data in line with Arend Lijphart’s (1999, 2012) empirical theory of democracy for 24 developed democracies between 1945 and 2010 are analyzed. Heteroscedastic multilevel models allow for directly modeling the development of the variance of types of democracy over time, revealing information about convergence, and adding substantial explanations. The findings indicate that there has been a trend away from extreme types of democracy in single cases, but no unconditional trend of convergence can be observed. However, there are conditional processes of convergence. In particular, economic globalization and the domestic veto structure interactively influence democratic convergence.
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Threo-methylphenidate is a chiral psychostimulant drug widely prescribed to treat attention-deficit hyperactivity disorder in children and adolescents. An enantioselective CE-based assay with head-column field-amplified sample stacking for analysis of threo-methylphenidate enantiomers in liquid/liquid extracts of oral fluid is described. Analytes are electrokinetically injected across a short water plug placed at the capillary inlet and become stacked at the interface between plug and buffer. Enantiomeric separation occurs within a few minutes in a pH 3.0 phosphate/triethanolamine buffer containing 20 mg/mL (2-hydroxypropyl)-β-CD as chiral selector. The assay with six point multilevel internal calibration provides a linear response for each enantiomer in the 10-200 ng/mL concentration range, is simple, inexpensive, and reproducible, and has an LOQ of 5 ng/mL. It was applied to oral fluid patient samples that were collected up to 12 h after intake of an immediate release tablet and two different extended release formulations with racemic methylphenidate. Drug profiles could thereby be assessed in a stereoselective way. Almost no levorotary threo-methylphenidate enantiomer was detected after intake of the two extended release formulations, whereas this enantiomer was detected during the first 2.5 h after intake of the immediate release preparation. The noninvasive collection of oral fluid is an attractive alternative to plasma for the monitoring of methylphenidate exposure in the pediatric community.
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Food security is important. A rising world population coupled with climate change creates growing pressure on global world food supplies. States alleviate this pressure domestically by attracting agri-foreign direct investment (agri-FDI). This is a high-risk strategy for weak states: the state may gain valuable foreign currency, technology and debt-free growth; but equally, investors may fail to deliver on their commitments and exploit weak domestic legal infrastructure to ‘grab’ large areas of prime agricultural land, leaving only marginal land for domestic production. A net loss to local food security and to the national economy results. This is problematic because the state must continue to guarantee its citizens’ right to food and property. Agri-FDI needs close regulation to maximise its benefit. This article maps the multilevel system of governance covering agri-FDI. We show how this system creates asymmetric rights in favour of the investor to the detriment of the host state’s food security and how these problems might be alleviated.
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AIM To investigate risk factors for the loss of multi-rooted teeth (MRT) in subjects treated for periodontitis and enrolled in supportive periodontal therapy (SPT). MATERIAL AND METHODS A total of 172 subjects were examined before (T0) and after active periodontal therapy (APT)(T1) and following a mean of 11.5 ± 5.2 (SD) years of SPT (T2). The association of risk factors with loss of MRT was analysed with multilevel logistic regression. The tooth was the unit of analysis. RESULTS Furcation involvement (FI) = 1 before APT was not a risk factor for tooth loss compared with FI = 0 (p = 0.37). Between T0 and T2, MRT with FI = 2 (OR: 2.92, 95% CI: 1.68, 5.06, p = 0.0001) and FI = 3 (OR: 6.85, 95% CI: 3.40, 13.83, p < 0.0001) were at a significantly higher risk to be lost compared with those with FI = 0. During SPT, smokers lost significantly more MRT compared with non-smokers (OR: 2.37, 95% CI: 1.05, 5.35, p = 0.04). Non-smoking and compliant subjects with FI = 0/1 at T1 lost significantly less MRT during SPT compared with non-compliant smokers with FI = 2 (OR: 10.11, 95% CI: 2.91, 35.11, p < 0.0001) and FI = 3 (OR: 17.18, 95% CI: 4.98, 59.28, p < 0.0001) respectively. CONCLUSIONS FI = 1 was not a risk factor for tooth loss compared with FI = 0. FI = 2/3, smoking and lack of compliance with regular SPT represented risk factors for the loss of MRT in subjects treated for periodontitis.
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Young peoples’ sport activity in Switzerland differs considerably depending on the linguistic region (Lamprecht, Fischer, & Stamm, 2008). This appears to be based on cultural as well as on structural differences. The question then arises how differing structural conditions in communes (e.g. sport facilities, significance of the municipal promotion of sport) across different linguistic regions of Switzerland cause variation in sport behaviour. Based on the theory of social action (Coleman, 1990), it is assumed that individual behaviour is not only determined by individual but also by structural and socio-cultural factors in which a person is socially embedded. In two case studies, multilevel data was gathered analysing possible influences of structural factors on sports behaviour. Using an online survey, 15 to 25 year old inhabitants (N = 205) living in a German and French speaking commune were questioned about their sports participation in and outside of their commune, as well as their perception of sport-related structural characteristics in their commune. To collect information about communes’ sport facilities, the sport providers (N = 23) were interviewed. Sport-related characteristics of the communes were also collected through two interviews with representatives of the municipal administration. As expected, sport participation is significantly lower in the French speaking commune (Chi2 (1, N = 205) = 3.84, p < .05). Adolescents and young adults living in the French speaking commune are less satisfied with the sport infrastructure (F(1,135) = 9.65, p < .01) and evaluate the opportunities to be physically active in their commune significantly worse (F(1,144) = 15.33, p < .01) than their German-speaking counterparts. These first findings show the impact of structural conditions in communes on sport participation of adolescents and young people. However, it must be noted that this study is explorative and further communes would need to be examined in order to generalize the results. References Coleman, J. S. (1990). Foundations of social theory. Cambridge, MA: Belknap. Lamprecht, M., Fischer, A. & Stamm, H. (2008). Sport Schweiz 2008. Das Sportverhalten der Schweizer Bevölkerung. Magglingen: BASPO.
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Introduction The physical activity of the Swiss population differs considerably depending on the linguistic region. German speakers are more often physically active than people living in the French- or Italian-speaking part of Switzerland (Stamm & Lamprecht, 2008). This study analyses how differing structural conditions in communes (e.g. sport facilities, significance of the municipal promotion of sport) across different linguistic regions of Switzerland correlate with physical activity and sports participation for adolescents and young adults. Methodological approach Based on the theory of social action (Coleman, 1990), it is assumed that individual behaviour is not only determined by individual but also by structural and socio-cultural factors in which a person is socially embedded. In two case studies, multilevel data was gathered analysing possible influences of structural factors on sports behaviour. Using an online survey, 15 to 25 year old inhabitants (N = 205) living in a German- and French-speaking commune were questioned about their sports participation in and outside of their commune, as well as their perception of sport-related structural characteristics in their commune. To collect information about communes’ sport facilities, the sport providers (N = 23) were interviewed. Sport-related characteristics of the communes were also collected through two interviews with representatives of the municipal administration. Results and discussion Physical activity is significantly higher (Chi2 (1, N = 183) = 4.78, p < .05) and sport participation is significantly lower in the French speaking commune (Chi2 (1, N = 205) = 3.84, p < .05). Adolescents and young adults in the French speaking commune (M = 3.15, SD = 1.23) are less satisfied with the opportunities to be physically active in the environment than their counterparts living in the German speaking commune (p < .001, Mann-Whitney U – test). These first findings show the impact of structural conditions in communes on physical activity and sport participation of adolescents and young people. However, it must be noted that this study is explorative and further communes would need to be examined in order to generalize the results. References Coleman J S (1990). Foundations of social theory. Belknap, Cambridge, MA. Stamm H, Lamprecht M (2008). EJSS, 8(1+2), 15-29.