Data fitting
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- MeSH
- akademie a ústavy organizace a řízení využití MeSH
- algoritmy MeSH
- finanční podpora výzkumu jako téma MeSH
- jaderná energie zákonodárství a právo MeSH
- lidé MeSH
- matematické výpočty počítačové MeSH
- radioaktivní znečištění ovzduší prevence a kontrola škodlivé účinky zákonodárství a právo MeSH
- statistické modely MeSH
- znečištění životního prostředí prevence a kontrola škodlivé účinky zákonodárství a právo MeSH
- Check Tag
- lidé MeSH
Cílem sdělení je upozornit na nekorektní přístupy, ke kterým dochází při statistickém zpracování dat. Kriticky zde hodnotíme situaci, kdy jsou vyškrtávány nehodící se údaje tak, aby výsledky odpovídaly předem stanovené hypotéze. Ukazujeme, jak je pro statistiku důležité znát kontext celé studie a okolnosti, za kterých byla data vygenerována. Upozorňujeme na nebezpečí, která plynou z mnohonásobného používání statistických testů významnosti na jednom vzorku dat.
The objective of the paper is to draw attention to incorrectness of variaous statistical approaches to research data. We critically assess the situation when first the decision on the hypothesis to be proved is done and then data are made to fit the hypothesis. We demonstrate that data cannot be satisfactorily interpreted without close attention to the manner of their collection. Finnaly we criticize opportunistic data tortuning when researcher explores the data until a significant result is found and then devises a biologically plausible hypothesis.
In this chapter, we demonstrate the advantage of the simultaneous multicurve nonlinear least-squares analysis over that of the conventional single-curve analysis. Fitting results are subjected to thorough Monte Carlo analysis for rigorous assessment of confidence intervals and parameter correlations. The comparison is performed on a practical example of simulated steady-state reaction kinetics complemented with isothermal calorimetry (ITC) data resembling allosteric behavior of rabbit muscle pyruvate kinase (RMPK). Global analysis improves accuracy and confidence limits of model parameters. Cross-correlation between parameters is also reduced with accompanying enhancement of the model-testing power. This becomes especially important for validation of models with "difficult" highly cross-correlated parameters. We show how proper experimental design and critical evaluation of data can improve the chance of differentiating models.
The study deals with the process of estimation of material parameters from uniaxial test data of arterial tissue and focuses on the role of transverse strains. Two fitting strategies are analyzed and their impact on the predictive and descriptive capabilities of the resulting model is evaluated. The standard fitting procedure (strategy A) based on longitudinal stress-strain curves is compared with the enhanced approach (strategy B) taking also the transverse strain test data into account. The study is performed on a large set of material data adopted from literature and for a variety of constitutive models developed for fibrous soft tissues. The standard procedure (A) ignoring the transverse strain test data is found rather hazardous, leading often to unrealistic predictions of the model exhibiting auxetic behaviour. In contrast, the alternative fitting method (B) ensures a realistic strain response of the model and is proved to be superior since it does not require any significant demands of computational effort or additional testing. The results presented in this paper show that even the artificial transverse strain data (i.e., not measured during testing but generated ex post based on assumed Poisson's ratio) are much less hazardous than total disregard of the transverse strain response.
- MeSH
- arterie * MeSH
- biologické modely * MeSH
- Publikační typ
- časopisecké články MeSH
Genome duplication (polyploidy) is a recurrent evolutionary process in plants, often conferring instant reproductive isolation and thus potentially leading to speciation. Outcome of the process is often seen in the field as different cytotypes co-occur in many plant populations. Failure of meiotic reduction during gametogenesis is widely acknowledged to be the main mode of polyploid formation. To get insight into its role in the dynamics of polyploidy generation under natural conditions, and coexistence of several ploidy levels, we developed a general gametic model for diploid-polyploid systems. This model predicts equilibrium ploidy frequencies as functions of several parameters, namely the unreduced gamete proportions and fertilities of higher ploidy plants. We used data on field ploidy frequencies for 39 presumably autopolyploid plant species/populations to infer numerical values of the model parameters (either analytically or using an optimization procedure). With the exception of a few species, the model fit was very high. The estimated proportions of unreduced gametes (median of 0.0089) matched published estimates well. Our results imply that conditions for cytotype coexistence in natural populations are likely to be less restrictive than previously assumed. In addition, rather simple models show sufficiently rich behaviour to explain the prevalence of polyploids among flowering plants.
... about Change 7 -- 1.3 Three Important Features of a Study of Change 9 -- 2 Exploring Longitudinal Data ... ... on Change 16 -- 2.1 Creating a Longitudinal Data Set 17 -- 2.2 Descriptive Analysis of Individual Change ... ... Estimated Variance Components 72 -- 4 Doing Data Analysis with the Multilevel Model for Change 75 -- ... ... the Cox Regression Model to Data 516 -- 14.3 Interpreting the Results of Fitting the Cox Regression ... ... Model to Data 523 -- 14.4 Nonparametric Strategies for Displaying the Results of Model Fitting 535 -- ...
xx, 644 s. : il, tab. ; 24 cm
- MeSH
- longitudinální studie MeSH
- sociální vědy metody MeSH
- výzkum MeSH
- výzkumný projekt MeSH
- Publikační typ
- monografie MeSH
- Konspekt
- Sociologie
- NLK Obory
- sociologie
The susceptible-infected-removed (SIR) and the susceptible-exposed-infected-removed (SEIR) epidemic models with constant parameters are adequate for describing the time evolution of seasonal diseases for which available data usually consist of fatality reports. The problems associated with the determination of system parameters starts with the inference of the number of removed individuals from fatality data, because the infection to death period may depend on health care factors. Then, one encounters numerical sensitivity problems for the determination of the system parameters from a correct but noisy representative of the number of removed individuals. Finally as the available data is necessarily a normalized one, the models fitting this data may not be unique. We prove that the parameters of the (SEIR) model cannot be determined from the knowledge of a normalized curve of "Removed" individuals and we show that the proportion of removed individuals, [Formula: see text], is invariant under the interchange of the incubation and infection periods and corresponding scalings of the contact rate. On the other hand we prove that the SIR model fitting a normalized curve of removed individuals is unique and we give an implicit relation for the system parameters in terms of the values of [Formula: see text] and [Formula: see text], where [Formula: see text] is the steady state value of [Formula: see text] and [Formula: see text] and [Formula: see text] are the values of [Formula: see text] and its derivative at the inflection point [Formula: see text] of [Formula: see text]. We use these implicit relations to provide a robust method for the estimation of the system parameters and we apply this procedure to the fatality data for the H1N1 epidemic in the Czech Republic during 2009. We finally discuss the inference of the number of removed individuals from observational data, using a clinical survey conducted at major hospitals in Istanbul, Turkey, during 2009 H1N1 epidemic.
- MeSH
- biologické modely MeSH
- chřipka lidská epidemiologie MeSH
- epidemie statistika a číselné údaje MeSH
- lidé MeSH
- matematické pojmy MeSH
- pandemie statistika a číselné údaje MeSH
- počítačová simulace MeSH
- roční období MeSH
- statistické modely * MeSH
- virus chřipky A, podtyp H1N1 MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Česká republika MeSH
- Turecko MeSH
1st ed. xvii, 438 s., grafy, tab.
Body length and body weight are two forms of the organism's genotype expression. The growth curve of body length in newborns, the growth curve of body height in children and adolescents, and the growth curve of body weight from birth to adolescence express the individual dynamics of the body length and body weight phenotype development. The body length growth curve from birth to maturity is, according to Karlberg, divided into three components: Infancy (I), Childhood (C), and Puberty (P). This paper shows that not only the body length growth curve expressed in length size parameters (D) but also the body weight growth (G) of individual boys corresponds to a growth curve composed of the three I-, C-, P- components expressed by the construction of three separate logistic curves. Each individual logistic curve component distinctly fits, within the defined probability, into the set of the measured phenotype values of body length (D) or body weight (G). Each of the fitted logistic curves is determined by the three constants referred to as the parameters of the Dynamic Phenotype. In the body length growth trait the parameters of the Dynamic Phenotype are (D0, DLi, dDmax) and in the body weight growth trait the parameters of the Dynamic Phenotype are (G0, GLi, dGmax) for each I-, C-, P- logistic curve component. It is shown that the Dynamic Phenotype parameter method described not only determines logistic curve components, but also enables exact construction of the whole individual I-, C-, P- growth curve composed of the corresponding I-, C-, P- sections of the logistic curves. Each I-, C-, P- logistic growth curve component begins by age (t0) and the initial value of the variable (X0) of the I-, C-, P- logistic curve component. The inflexion point of the growth curve component marked by age (t*(X)) indicates the age of the maximal growth velocity of the variables (dXmax). The Dynamic Phenotype method can also be applied to the growth data represented by the average values estimated in the reference groups of probands and to the interpretation of the percentile growth curves.
- MeSH
- biometrie metody MeSH
- dítě MeSH
- fenotyp MeSH
- financování organizované MeSH
- lidé MeSH
- logistické modely MeSH
- longitudinální studie MeSH
- mladiství MeSH
- růst fyziologie MeSH
- statistika jako téma metody MeSH
- tělesná hmotnost fyziologie genetika MeSH
- tělesná výška fyziologie genetika MeSH
- vývoj dítěte fyziologie MeSH
- Check Tag
- dítě MeSH
- lidé MeSH
- mladiství MeSH
Ultrasound guidance is used for many surgical interventions such as biopsy and electrode insertion. We present a method to localize a thin surgical tool such as a biopsy needle or a microelectrode in a 3-D ultrasound image. The proposed method starts with thresholding and model fitting using random sample consensus for robust localization of the axis. Subsequent local optimization refines its position. Two different tool image models are presented: one is simple and fast and the second uses learned a priori information about the tool's voxel intensities and the background. Finally, the tip of the tool is localized by finding an intensity drop along the axis. The simulation study shows that our algorithm can localize the tool at nearly real-time speed, even using a MATLAB implementation, with accuracy better than 1 mm. In an experimental comparison with several alternative localization methods, our method appears to be the fastest and the most robust one. We also show the results on real 3-D ultrasound data from a PVA cryogel phantom, turkey breast, and breast biopsy.
- MeSH
- algoritmy MeSH
- chirurgie s pomocí počítače metody MeSH
- elektrody MeSH
- fantomy radiodiagnostické MeSH
- hydrogely MeSH
- jehly MeSH
- krocani MeSH
- kryogely MeSH
- lidé MeSH
- maso MeSH
- počítačová simulace MeSH
- polyvinylalkohol MeSH
- prsy MeSH
- statistické modely MeSH
- ultrasonografie metody MeSH
- zobrazování trojrozměrné metody MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
