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Fitting Model (fitting + model)
Selected AbstractsMaximum likelihood constrained deconvolution.CONCEPTS IN MAGNETIC RESONANCE, Issue 6 2002I: Algorithm, qualitative, quantitative enhancement in synthetic two-dimensional NMR spectra Abstract The maximum likelihood method is a constrained iterative spectral deconvolution technique in which a spectral fitting model is determined by minimizing the variance of fit in the time domain in a nonlinear iterative manner. Application of this method to synthetic 2-dimensional (2-D) NMR spectra, which have heavily overlapped multiplets associated with low signal to noise ratios, yields contrast-enhanced spectra with simultaneous noise suppression and resolution improvement. This protocol greatly facilitates peak recognition and often partitions overlapping multiplets into individual components, leading to a more accurate interpretation of resonance frequencies, coupling constants, and multiplets than does the conventional apodization or Fourier transform method. These advantages are useful for constructing reliable 3-D molecular structures for complex molecular systems. © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 402,415, 2002 [source] Assessment of Family Functioning in Caucasian and Hispanic Americans: Reliability, Validity, and Factor Structure of the Family Assessment DeviceFAMILY PROCESS, Issue 4 2007GREGORY A. AARONS PH.D. The purpose of this study was to examine the factor structure, reliability, and validity of the Family Assessment Device (FAD) among a national sample of Caucasian and Hispanic American families receiving public sector mental health services. A confirmatory factor analysis conducted to test model fit yielded equivocal findings. With few exceptions, indices of model fit, reliability, and validity were poorer for Hispanic Americans compared with Caucasian Americans. Contrary to our expectation, an exploratory factor analysis did not result in a better fitting model of family functioning. Without stronger evidence supporting a reformulation of the FAD, we recommend against such a course of action. Findings highlight the need for additional research on the role of culture in measurement of family functioning. [source] Comparison of spectral fitting methods for overlapping J-coupled metabolite resonancesMAGNETIC RESONANCE IN MEDICINE, Issue 3 2010A. Gonenc Abstract There is increasing interest in the use of two-dimensional J-resolved spectroscopic acquisition (multiecho) methods for in vivo proton magnetic resonance spectroscopy due to the improved discrimination of overlapping J-coupled multiplet resonances that is provided. Of particular interest is the potential for discrimination of the overlapping resonances of glutamate and glutamine. In this study, a new time-domain parametric spectral model that makes use of all available data is described for fitting the complete two-dimensional multiecho data, and the performance of this method was compared with fitting of one-dimensional spectra obtained following averaging multiecho data (echo time-averaged) and single-echo time PRESS (Point Resolved Spectroscopy) acquired spectra. These methods were compared using data obtained from a phantom containing typical brain metabolites and a human brain. Results indicate that improved performance and accuracy is obtained for the two-dimensional acquisition and spectral fitting model. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Statistical hypothesis testing in intraspecific phylogeography: nested clade phylogeographical analysis vs. approximate Bayesian computationMOLECULAR ECOLOGY, Issue 2 2009ALAN R. TEMPLETON Abstract Nested clade phylogeographical analysis (NCPA) and approximate Bayesian computation (ABC) have been used to test phylogeographical hypotheses. Multilocus NCPA tests null hypotheses, whereas ABC discriminates among a finite set of alternatives. The interpretive criteria of NCPA are explicit and allow complex models to be built from simple components. The interpretive criteria of ABC are ad hoc and require the specification of a complete phylogeographical model. The conclusions from ABC are often influenced by implicit assumptions arising from the many parameters needed to specify a complex model. These complex models confound many assumptions so that biological interpretations are difficult. Sampling error is accounted for in NCPA, but ABC ignores important sources of sampling error that creates pseudo-statistical power. NCPA generates the full sampling distribution of its statistics, but ABC only yields local probabilities, which in turn make it impossible to distinguish between a good fitting model, a non-informative model, and an over-determined model. Both NCPA and ABC use approximations, but convergences of the approximations used in NCPA are well defined whereas those in ABC are not. NCPA can analyse a large number of locations, but ABC cannot. Finally, the dimensionality of tested hypothesis is known in NCPA, but not for ABC. As a consequence, the ,probabilities' generated by ABC are not true probabilities and are statistically non-interpretable. Accordingly, ABC should not be used for hypothesis testing, but simulation approaches are valuable when used in conjunction with NCPA or other methods that do not rely on highly parameterized models. [source] Pathological personality traits and externalizing behaviourPERSONALITY AND MENTAL HEALTH, Issue 1 2009Lauren R. Pryor Previous research has identified general personality traits and personality disorders that are associated with externalizing behaviour (EB). There is a dearth of research, however, investigating the relations between pathological personality traits and EB. The current study examined pathological personality traits, as measured by the Schedule for Non-adaptive and Adaptive Functioning (SNAP) and the Dimensional Assessment of Personality Pathology-Basic Questionnaire (DAPP-BQ), in relation to EB. Undergraduates (n = 228) completed the SNAP, DAPP-BQ, and a measure of antisocial behaviour, substance use, gambling, intimate partner violence and risky sexual behaviour. Using confirmatory factor analysis, we identified the best fitting model as one that specified eight factors: five personality factors composed of constructs assessed by the DAPP and SNAP, one externalizing factor and two method factors corresponding to each of the measures. Consistent with the empirical literature using general personality traits, the current results suggest that pathological personality traits related to impulse control (i.e. low conscientiousness), as well as more interpersonally focused traits (i.e. low agreeableness), were most strongly associated with EB. Copyright © 2009 John Wiley & Sons, Ltd. [source] Error rate on the antisaccade task: Heritability and developmental change in performance among preadolescent and late-adolescent female twin youthPSYCHOPHYSIOLOGY, Issue 5 2002Stephen M. Malone We examined heritability of error rate on the antisaccade task among female twin youths. This task appears to be sensitive to prefrontal functioning, providing a measure of individual differences in inhibitory control associated with genetic risk for schizophrenia. The sample consisted of 674 11-year-olds and 616 17-year-olds, comprising the two cohorts of female twins from the Minnesota Twin Family Study, a population-based investigation of substance abuse and related psychopathology. We used biometric model-fitting methods to determine the relative magnitude of genetic and environmental influences on performance. In both age cohorts, the best fitting model contained additive genes and nonshared environment. Despite substantial age-related differences in mean performance levels (effect size = .81), additive genes accounted for greater than half the variance in performance in both age cohorts. These results are consistent with the hypothesis that antisaccade error rate might serve as an endophenotype for behavior disorders reflecting frontal lobe dysfunction or problems with inhibitory control. [source] Attributing Hardy-Weinberg Disequilibrium to Population Stratification and Genetic Association in Case-Control StudiesANNALS OF HUMAN GENETICS, Issue 1 2010Vaneeta K. Grover Summary Loci exhibiting Hardy-Weinberg disequilibrium (HWD) are often excluded from association studies, because HWD may indicate genotyping error, population stratification or selection bias. For case-control studies, HWD can result from a genetic effect at the locus. We extend the modelling to accommodate both stratification and genetic effects. Theoretical genotype frequencies and HWD coefficients are derived under a general genetic model for a population with two strata. Maximum likelihood is used to estimate model parameters and a test for lack of fit identifies the models most consistent with the data. Simulations were used to assess the method. The technique was applied to a group of ethnically and clinically heterogeneous kidney stone formers and controls, both exhibiting HWD for the R990G SNP of the CASR gene. Results indicate the best fitting model incorporates both stratification and genetic association. The ability of our method to apportion HWD to stratification and genetic effects may well be a significant advance in dealing with heterogeneity in case-control genetic association studies. [source] Seasonal dynamics, dispersion, sequential sampling plans and treatment thresholds for the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in a mature lemon block in coastal New South Wales, AustraliaAUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 3 2008Zhong Min Liu Abstract, Studies of citrus leafminer in a coastal orchard in NSW, Australia indicated that an increase in abundance to about one mine per flush was followed during the midseason flush by a rapid increase in population that was related to an increase in the percentage of leaves infested within flushes and the number of mines per leaf. The fits of frequency distributions and Iwao's patchiness regression indicated that populations were highly contagious initially, and as the exponent k of the negative binomial distribution increased with increasing population density, the distribution approached random. Concurrently, the coefficient of variation of mines per flush (which was strongly related to the proportion of un-infested flushes) decreased to about unity as the proportion of un-infested flushes reached zero and fell further as the number of mines per flush increased. Both numerative and binomial sequential sampling plans were developed using a decision threshold based on 1.2 mines per flush. The binomial sampling plan was based on a closely fitting model of the functional relationship between mean density and proportion of infested flushes. Functional relationships using the parameters determined from Iwao's patchiness regression and Taylor's power law were equally satisfactory, and one based on the negative binomial model also fitted well, but the Poisson model did not. The three best fitting models indicated that a decision threshold of 1.2 mines per flush was equivalent to 50% of flushes infested. From a practical point of view, the transition from 25% infestation of flushes through 50% is so rapid that it may be prudent to take action when the 25% level is reached; otherwise, the 50% may be passed before the crop is checked again. For valuable nursery stock should infestation be detected in spring, it may be advisable to apply prophylactic treatment as the midseason flush starts. [source] |