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PubMed1961

Keys to cultural understanding.

Figures of speech are tangible manifestations of deeply rooted modes of perception and conceptualization. They represent categories or models for interpreting the universe-natural and supernatural, and material and non-material phenomena. These categories or models are reflected in all aspects of culture and are fundamentally determined by culture. They should not be considered universal but, rather, extremely relative and highly variable. Some students of language and culture, such as Whorf, would consider figures of speech not to be the most important organizing categories and would give precedence to grammatical constructions-that is, subject-predicate division or verb tenses. The use of figures of speech, however, is in some ways more easily investigated than grammatical categories, and their analysis can provide both unique and corroborative insights into various aspects of a culture, as has been demonstrated here with Palauan social organization.

Child↗

PubMed2004

Interpreting the parameters of the diffusion model: an empirical validation.

The diffusion model (Ratcliff, 1978) allows for the statistical separation of different components of a speeded binary decision process (decision threshold, bias, information uptake, and motor response). These components are represented by different parameters of the model. Two experiments were conducted to test the interpretational validity of the parameters. Using a color discrimination task, we investigated whether experimental manipulations of specific aspects of the decision process had specific effects on the corresponding parameters in a diffusion model data analysis (see Ratcliff, 2002; Ratcliff & Rouder, 1998; Ratcliff, Thapar, & McKoon, 2001, 2003). In support of the model, we found that (1) decision thresholds were higher when we induced accuracy motivation, (2) drift rates (i.e., information uptake) were lower when stimuli were harder to discriminate, (3) the motor components were increased when a more difficult form of response was required, and (4) the process was biased toward rewarded responses.

Adult↗

PubMed1990

Comments on a time-dependent version of the linear-quadratic model.

The accuracy and interpretation of the "LQ + time" model (E = D(alpha + beta d) - gamma T) are discussed. Evidence is presented, based on data in the literature, that this model does not accurately describe the changes in isoeffect dose occurring with protraction of the overall treatment time during fractionated irradiation of the lung. This lack of fit of the model explains, in part, the surprisingly large values of gamma/alpha that have been derived from experimental lung data. The large apparent time factors for lung suggested by the model are also partly explained by the fact that gamma T/alpha, despite having units of dose, actually measures the influence of treatment time on the effect scale, not the dose scale, and is shown to consistently overestimate the change in total dose. The unusually high values of alpha/beta that have been derived for lung using the model (approximately 5 Gy) are shown to be influenced by the method by which the model was fitted to data. Reanalyses of the data using a more statistically valid regression procedure produce estimates of alpha/beta more typical of those usually cited for lung (approximately 3 Gy). Most importantly, published isoeffect data from lung indicate that the true deviation from the linear-quadratic (LQ) model is nonlinear in time, instead of linear, and also depends on other factors such as the effect level and the size of dose per fraction. Thus, we do not advocate the use of the "LQ + time" expression as a general isoeffect model.

Animals↗

PubMed1998

Use of structural equation modeling to test the construct validity of the SF-36 Health Survey in ten countries: results from the IQOLA Project. International Quality of Life Assessment.

A crucial prerequisite to the use of the SF-36 Health Survey in multinational studies is the reproduction of the conceptual model underlying its scoring and interpretation. Structural equation modeling (SEM) was used to test these aspects of the construct validity of the SF-36 in ten IQOLA countries: Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden, the United Kingdom, and the United States. Data came from general population surveys fielded to gather normative data. Measurement and structural models developed in the United States were cross-validated in random halves of the sample in each country. SEM analyses supported the eight first-order factor model of health that underlies the scoring of SF-36 scales and two second-order factors that are the basis for summary physical and mental health measures. A single third-order factor was also observed in support of the hypothesis that all responses to the SF-36 are generated by a single, underlying construct--health. In addition, a third second-order factors, interpreted as general well-being, was shown to improve the fit of the model. This model (including eight first-order factors, three second-order factors, and one third-order factor) was cross-validated using a holdout sample within the United States and in each of the nine other countries. These results confirm the hypothesized relationships between SF-36 items and scales and justify their scoring in each country using standard algorithms. Results also suggest that SF-36 scales and summary physical and mental health measures will have similar interpretations across countries. The practical implications of a third second-order SF-36 factor (general well-being) warrant further study.

Cross-Cultural Comparison↗

PubMed1998

Extending the simple linear regression model to account for correlated responses: an introduction to generalized estimating equations and multi-level mixed modelling.

Much of the research in epidemiology and clinical science is based upon longitudinal designs which involve repeated measurements of a variable of interest in each of a series of individuals. Such designs can be very powerful, both statistically and scientifically, because they enable one to study changes within individual subjects over time or under varied conditions. However, this power arises because the repeated measurements tend to be correlated with one another, and this must be taken into proper account at the time of analysis or misleading conclusions may result. Recent advances in statistical theory and in software development mean that studies based upon such designs can now be analysed more easily, in a valid yet flexible manner, using a variety of approaches which include the use of generalized estimating equations, and mixed models which incorporate random effects. This paper provides a particularly simple illustration of the use of these two approaches, taking as a practical example the analysis of a study which examined the response of portable peak expiratory flow meters to changes in true peak expiratory flow in 12 children with asthma. The paper takes the reader through the relevant practicalities of model fitting, interpretation and criticism and demonstrates that, in a simple case such as this, analyses based upon these model-based approaches produce reassuringly similar inferences to standard analyses based upon more conventional methods.

Adolescent↗

PubMedDate not supplied

Multiplicative and additive models with external controls in a cohort study of cancer mortality.

The use of additive and multiplicative hazard models is examined for a cohort study of 2696 women followed up for 12 years. The multiplicative model implied that women with a haemoglobin level less than 12 g/dl were at higher risk from cancer, and the additive model showed that this risk was confined to women after the menopause. Despite difficulties in fitting and in interpretation, additive model can be useful in the analysis of cohort studies.

Adult↗

PubMed2005

Influence of erythromycin A on the microbial populations in aquaculture sediment microcosms.

Degradation of erythromycin A was studied using two sediment samples obtained from the salmon and trout hatchery sites at Hupp Springs (HS) and Goldendale (GD), Washington, United States. The former site had been treated for 3 years with erythromycin-medicated feed prior to the experiments, and the latter site had not been treated with any antibiotic for at least 6 years. The two sediment microcosms treated with either N-[methyl-14C]erythromycin A or [1,3,5,7,9,11,13-14C]erythromycin A showed S-curves for erythromycin A mineralization with a prolonged lag time of 120 days, except for GD microcosms treated with [1,3,5,7,9,11,13-14C]erythromycin A. We proposed a simplified logistic model to interpret the mineralization curves under the assumption of the low densities of initial populations metabolizing erythromycin A. The model was helpful for knowing the biological potential for erythromycin A degradation in sediments. Although erythromycin A added to the two sediment microcosms did not significantly alter the numbers of total viable aerobic bacteria or erythromycin-resistant bacteria, it affected the bacterial composition. The influence on the bacterial composition appeared to be greater in GD microcosms without pre-exposure to antibiotics. PCR-RFLP and DNA sequence analyses of the 16S ribosomal RNA gene and the erythromycin esterase (ere) gene revealed that ereA type 2 (ereA2) was present in potentially erythromycin-degrading Pseudomonas spp. strains GD100, GD200, HS100, HS200 and HS300, isolated from erythromycin-treated and non-treated GD and HS microcosms. Erythromycin A appeared to influence the development and proliferation of strain GD200, possibly via the lateral gene transfer of ereA2.

Anti-Bacterial Agents↗

PubMed1999

Direct three-dimensional localization and positive identification of RNA helices within the ribosome by means of genetic tagging and cryo-electron microscopy.

BACKGROUND: Ribosomes are complex macromolecular machines that perform the translation of the genetic message. Cryo-electron microscopic (cryo-EM) maps of the Escherichia coli 70S ribosome are approaching a resolution of 10 A and X-ray maps of the 30S and 50S subunits are now available at 5 A. These maps show a lot of details about the inner architecture of the ribosome and ribosomal RNA helices are clearly visible. However, in the absence of further biological information, even at the higher resolution of the X-ray maps many rRNA helices can be placed only tentatively. Here we show that genetic tagging in combination with cryo-EM can place and orient double-stranded RNA helices with high accuracy. RESULTS: A tRNA sequence inserted into the E. coli 23S ribosomal RNA gene, at one of the points of sequence expansion in eukaryotic ribosomes, is visible in the cryo-EM map as a peripheral 'foot' structure. By tracing its acceptor-stem end, the location of helix 63 in domain IV and helix 98 in domain VI of the 50S subunit could be precisely determined. CONCLUSIONS: Our study demonstrates for the first time that features of a three-dimensional cryo-EM map of an asymmetric macromolecular complex can be interpreted in terms of secondary and primary structure. Using the identified helices as a starting point, it is possible to model and interpret, in molecular terms, a larger portion of the ribosome. Our results might be also useful in interpreting and refining the current X-ray maps.

Base Sequence↗

PubMed2006

Improving methods of assessing natural killer cell cytotoxicity.

Natural killer (NK) cells are a class of lymphocytes important in immune resistance to viral and other serious diseases. The cytotoxic function, or 'killing activity' of NK cells has become important in studies of the effects of stress and other psychosocial factors on physical health. Unfortunately, research on NK cell function has been plagued by discrepancies in the methods of interpreting NK cytotoxicity data. We briefly review some of the variations in measuring NK cell activity and present a new model for interpreting these results, introducing maximal target cell lysis (A) and the slope of the cytolytic curve (k) as parameters that attempt to make full use of the information and the statistical power in NK cell cytotoxicity data. Examples of these interpretation methods are presented using NK cytotoxicity data from a group of metastatic breast cancer patients. This approach will be useful in applications of NK cell measurement in psychoneuroimmunology research.

Analysis of Variance↗

PubMed1995

Some limitations of spatio temporal source models.

The spatio temporal source model (STSM) interprets the successive scalp topographies of an electrophysiological event as the summed activity of a few fixed generators. This modeling methodology is expected to provide a unique solution for a fixed number of sources. Because in general there is no "a priori" available physiological information, independent criteria need to be applied for determining the correct number of sources (Ns). This study illustrates theoretically as well as in simulations, that the existence of a unique solution can only be claimed when Ns is known a priori. Since most of the methods proposed for estimate Ns are not accurate as illustrated here, STSM may result in unpredictable non-physiological solutions. Basic modeling aspects and additional factors affecting reliability of STSM such as those related to the optimization process associated to the source parameter search are discussed. Some of the possible inverse solutions are illustrated in our simulations. Our main conclusion is the need to improve STSM before claims about neural generator localization can be accepted. We will also discuss, how attempts to apply STSM to clinical data, apparently supporting their reliability, are plagued with incorrect assumptions and do not justify the expectancy aroused about such models. We discuss some ways for improving STSM and the need to develop measures to evaluate their reliability, independent of the physiological plausibility of the solutions obtained. Finally we propose two mathematical measures that can be incorporated to the optimization process to contribute to the evaluation of its performance.

Algorithms↗

PubMed2006

Kinetics of liquid phase semiconductor photoassisted reactions: supporting observations for a pseudo-steady-state model.

The kinetics of liquid phase semiconductor photocatalytic and photoassisted reactions are an area of some debate, reignited recently by an article by Ollis(1) in which he proposed a simple pseudo-steady-state model to interpret the Langmuir-Hinshelwood type kinetics, commonly observed in such systems. In the current article, support for this model, over other models, is provided by a reinterpretation of the results of a study, reported initially in 1999,(2) of the photoassisted mineralization of 4-chlorophenol, 4-CP, by titania films and dispersions as a function of incident light intensity, I. On the basis of this model, these results indicate that 4-CP is adsorbed more strongly on P25 TiO2 when it is in a dispersed, rather than a film form, due to a higher rate constant for adsorption, k(1). In addition, the kinetics of 4-CP removal appear to depend on I(beta), where beta = 1 or 0.6 for when the TiO2 is in a film or a dispersed form, respectively. These findings are discussed both in terms of the pseudo-steady-state model and other popular kinetic models.

Journal Article↗

PubMed2003

Movement systems as dynamical systems: the functional role of variability and its implications for sports medicine.

In recent years, concepts and tools from dynamical systems theory have been successfully applied to the study of movement systems, contradicting traditional views of variability as noise or error. From this perspective, it is apparent that variability in movement systems is omnipresent and unavoidable due to the distinct constraints that shape each individual's behaviour. In this position paper, it is argued that trial-to-trial movement variations within individuals and performance differences observed between individuals may be best interpreted as attempts to exploit the variability that is inherent within and between biological systems. That is, variability in movement systems helps individuals adapt to the unique constraints (personal, task and environmental) impinging on them across different timescales. We examine the implications of these ideas for sports medicine, by: (i) focusing on intra-individual variability in postural control to exemplify within-individual real-time adaptations to changing informational constraints in the performance environment; and (ii) interpreting recent evidence on the role of the angiotensin-converting enzyme gene as a genetic (developmental) constraint on individual differences in physical performance. The implementation of a dynamical systems theoretical interpretation of variability in movement systems signals a need to re-evaluate the ubiquitous influence of the traditional 'medical model' in interpreting motor behaviour and performance constrained by disease or injury to the movement system. Accordingly, there is a need to develop new tools for providing individualised plots of motor behaviour and performance as a function of key constraints. Coordination profiling is proposed as one such alternative approach for interpreting the variability and stability demonstrated by individuals as they attempt to construct functional, goal-directed patterns of motor behaviour during each unique performance. Finally, the relative contribution of genes and training to between-individual performance variation is highlighted, with the conclusion that dynamical systems theory provides an appropriate multidisciplinary theoretical framework to explain their interaction in supporting physical performance.

Adaptation, Physiological↗

PubMed1970

Conduction mechanisms in Lillie's iron-wire model of nerve.

Based on theory and experiment, we found that the conduction through the oxide film in Lillie's iron-wire model is dominated by Schottky emission at low fields (below 10(6) v/cm), by electron tunneling from trap to trap at intermediate fields and by direct tunneling (Fowler-Nordheim type) at higher fields (above 3 x 10(6) v/cm). The trap-to-trap tunneling is considered to give rise to the negative resistance and the fixed position of the current maximum as observed. Some of the nervelike properties of the Lillie's model are interpreted on this tunneling mechanism.

Electrophysiology↗

PubMed1996

Design and analysis of lipid tracer kinetic studies.

A fundamental problem in lipid metabolism is designing experiments to quantitate the kinetics of the plasma lipids and lipoproteins in the body. Tracers have been used extensively. In this review, we will combine our knowledge of the theory and application of tracer kinetic studies to discuss current state of the art methodologies for lipid metabolism. We will review the use of stable and radioactive isotopes pointing out the importance of the measurement variables, and the theory and application of noncompartmental and compartmental models to interpret the data.

Humans↗

PubMed1978

General theory of critical periods and development of obesity.

The general systems theory (GST), the general theory of organization (GTO), and the general theory of critical periods (GTCP) have been applied to some nutritional problems. This theoretical approach seems to be in good agreement with most of the data of the literature and with the personal experience, pointing at the possibility to use a simple general model to interpret the complex problem of obesity.

Critical Period, Psychological↗

PubMed1991

A framework for the interpretation of first-order interaction in logit modeling.

Several suggestions have been tendered for interpreting first-order interaction in log-linear analysis. Occasionally these methods result either in a loss of information or in results that are difficult to grasp on an intuitive level. It is argued that interpreting effect parameters in terms of odds ratios provides an elegant and intuitively appealing conceptual framework that has great generality across models. The interaction term then resembles a cross-product term in linear regression. In both forms of analysis, the partial effect of a given predictor on the response is composed of a constant and a correction that is a function of the other predictor involved in the interaction. This framework is especially appealing for models in which the logit is based on a bifurcation of the dependent variable. Although odds ratios are still useful for summarizing effects on polytomous dependent variables, greater caution must be exercised to avoid misleading interpretations.

Humans↗

PubMed2004

A mechanistic model of the actin cycle.

We have derived a broad, deterministic model of the steady-state actin cycle that includes its major regulatory mechanisms. Ours is the first model to solve the complete nucleotide profile within filaments, a feature that determines the dynamics and geometry of actin networks at the leading edges of motile cells, and one that has challenged investigators developing models to interpret steady-state experiments. We arrived at the nucleotide profile through analytic and numerical approaches that completely agree. Our model reproduces behaviors seen in numerous experiments with purified proteins, but allows a detailed inspection of the concentrations and fluxes that might exist in these experiments. These inspections provide new insight into the mechanisms that determine the rate of actin filament treadmilling. Specifically, we find that mechanisms for enhancing Pi release from the ADP.Pi intermediate on filaments, for increasing the off rate of ADP-bound subunits at pointed ends, and the multiple, simultaneous functions of profilin, make unique and essential contributions to increased treadmilling. In combination, these mechanisms have a theoretical capacity to increase treadmilling to levels limited only by the amount of available actin. This limitation arises because as the cycle becomes more dynamic, it tends toward the unpolymerized state.

Actins↗

PubMed1992

A neural network model as a globally coupled map and applications based on chaos.

First, a neural network model as the globally coupled map (GCM) is proposed. The model is obtained by modification of a Hopfield network model that has a negative self-feedback connection. Second, information processed by this model is interpreted in terms of the variety of the maps acting on the network elements, and a new, dynamic information processing model is described. The search for information using vague keywords, and solution of the traveling salesman problem (TSP) are introduced as applications.

Journal Article↗