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PubMed2001

A longitudinal study of children's juice intake and growth: the juice controversy revisited.

OBJECTIVES: To determine associations between children's longitudinal juice intake and growth parameters at age 72 months and to determine children's beverage intake patterns over time. SUBJECTS/SETTING: White children (n = 72) residing in the vicinity of a Southern US city participated in a longitudinal study. METHODS: Seven in-home interviews were conducted per child when each child was between 24 and 72 months of age. The 7 sets of 3-day dietary data were analyzed for beverage intake, categorized as juice (100% juice only), milk, carbonated beverages, and other drinks (e.g., lemonade, tea, juice drinks). The following growth parameters were determined for each child at age 72 months: height, weight, body mass index (measured as kg/m2), and ponderal index (measured as kg/m3); the 3 latter are measures of overweight. STATISTICAL ANALYSES: Associations between longitudinal juice intake and each growth parameter were tested with general linear models. Repeated measures analysis of variance tested changes in beverage intakes over time. RESULTS: There were no statistically significant associations between juice and children's height, weight, or body mass index, as tested by general linear models. Children's longitudinal juice intake was negatively related to ponderal index (beta = 0.065, P = .050). Children's juice intake decreased significantly between ages 2 and 6 years, from 6.8 to 3.6 oz/day (P = .0001); intakes of carbonated beverages and other drinks increased from 1.7 to 3.8 oz/day (P = .0016) and from 2.7 to 6.2 oz/day (P = .0001), respectively. APPLICATIONS/CONCLUSIONS: Children's longitudinal juice intake was not associated with either short stature or overweight. As juice consumption decreased, intakes of less nutritious beverages increased. Consumption of 100% juices should be encouraged by health professionals and parents/caregivers.

Analysis of Variance↗

PubMed1999

Parametric time-varying spectrum and its application to SEMG signals.

Frequency spectrum of surface electromyographic signals (SEMGs) exhibits a non-stationary nature even in case of constant level isometric muscle contractions. This changes are related to muscle fatigue processes and can be evaluated by methods for estimation of time-varying (TV) spectrum. We describe a two estimation techniques: sliding window approach and decomposition of linear model coefficients trajectories. Drawback of the first is its large variance which causes unrealistic abrupt changes in the curve of overall dynamics, calculated either as the second derivative of the MF or as the ARMA distance between subsequent linear models forming the TV parametric spectrum. We demonstrate, that the second method is more appropriate for description of a slowly changing spectrum of surface EMG signals. Dynamics measures obtained from this estimation are proposed as an indication of the fatigue process character.

Electromyography↗

PubMed1997

Functional identification of the input-output transforms of motoneurones in the rat and cat.

1. We studied the responses of rat hypoglossal and cat lumbar motoneurones to a variety of excitatory and inhibitory injected current transients during repetitive discharge. The amplitudes and time courses of the transients were comparable to those of the synaptic currents underlying unitary and small compound postsynaptic potentials (PSPs) recorded in these cells. Poisson trains of ten of these excitatory and ten inhibitory current transients were combined with an additional independent, high-frequency random waveform to approximate band limited white noise. The white noise waveform was then superimposed on long duration (39 s) suprathreshold current steps. 2. We measured the effects of each of the current transients on motoneurone discharge by compiling peristimulus time histograms (PSTHs) between the times of occurrence of individual current transients and motoneurone discharges. We estimated the changes in membrane potential associated with each current transient by approximating the passive response of the motoneurone with a simple resistance-capacitance circuit. The relations between the features of these simulated PSPs and those of the PSTHs were similar to those reported previously for real PSPs: the short-latency PSTH peak (or trough) was generally longer than the initial phase of the PSP derivative, but shorter than the time course of the PSP itself. Linear models of the PSP to PSTH transform based on the PSP time course, the time derivative of the PSP, or a linear combination of the two parameters could not reproduce the full range of PSTH profiles observed. 3. We also used the responses of the motoneurones to the white noise stimulus to derive zero-, first- and second-order Wiener kernels, which provide a quantitative description of the relation between injected current and discharge probability. The convolution integral computed for an injected current waveform and the first-order Wiener kernel should provide the best linear prediction of the associated PSTH. This linear model provided good matches to the PSTHs associated with a wide range of current transients. However, for the largest amplitude current transients, a significant improvement in the PSTH match was often achieved by expanding the model to include the convolution of the second-order Wiener kernel with the input. 4. The overall transformation of current inputs into firing rate could be approximated by a second-order Wiener model, i.e. a cascade of a dynamic, linear filter followed by a static non-linearity. At a given mean firing rate, the non-linear component of the response of the motoneurone could be described by the square of the linear component multiplied by a constant coefficient. The amplitude of the response of the linear component increased with the average firing rate, whereas the value of the multiplicative coefficient in the non-linear component decreased. As a result, the overall transform could be predicted from the mean firing rate and the linear impulse response, yielding a relatively simple, general description of the motoneurone input-output function.

Action Potentials↗

PubMed1997

Glycosylated hemoglobin level and carotid intimal-medial thickening in nondiabetic individuals. The Atherosclerosis Risk in Communities Study.

OBJECTIVE: People with diabetes are at increased risk for cardiovascular events. However, questions remain about what role, if any, homeostatic glucose control plays in the development of cardiovascular disease among nondiabetic individuals. We investigated the relationship between HbA1c level and carotid intimal-medial thickening in normoglycemic individuals. RESEARCH DESIGN AND METHODS: We conducted a case-control study among 208 normoglycemic individuals (fasting glucose < or = 6.4 mmol/l and no history of diabetes) who had carotid initial-medial thickening (case subjects) and 208 normoglycemic control subjects individually matched for age, sex, race, field center, and date of exam. Subjects were free-living men and women, aged 45-64 years at baseline, who participated in the Atherosclerosis Risk in Communities (ARIC) Study. RESULTS: HbA1c levels, expressed as percent of total hemoglobin, ranged from 4 to 7% and correlated only modestly with single measurements of fasting glucose (r = 0.16) and fasting insulin (r = 0.14). The mean level of HbA1c was 5.18% among case subjects and 5.07% among control subjects (P = 0.004, paired t test). As compared with the first quartile of HbA1c the matched relative odds of being a case were 1.15, 1.33, and 2.30 for the second, third, and fourth quartiles, respectively (P = 0.005 for linear trend). After multivariate adjustment for age, fasting glucose, fasting insulin, BMI, smoking status, hypertension, LDL cholesterol, HDL cholesterol, fibrinogen, and education level, the respective relative odds estimates were 0.98, 1.07, and 1.88 (P = 0.16 for linear trend). When modeled linearly as a continuous variable and after adjustment for the above-mentioned covariates, a 1% point increment in HbA1c level was associated with 1.77 greater odds of being a case (95% CI, 0.9-3.5). CONCLUSIONS: These data provide some support to the hypothesis that in the absence of diabetes, homeostatic glycemic control is a risk factor for atherosclerosis.

Arteriosclerosis↗

PubMed1993

Technical note: computing tests of fixed effects in a restricted class of mixed models.

Inferences about fixed effects in mixed linear models are important in a variety of animal science studies. The statistical theory for making such inferences is well known, and if the variance components are known up to a proportionality constant, then optimal exact tests can be performed. Computing the test statistics, however, can still be problematic when the random effects have many levels. In practice, approximate tests that are easily computed but less efficient are usually employed. This article describes reduction in error sum of squares procedures for performing the exact test and for computing associated confidence intervals. By taking advantage of iterative algorithms for solving Henderson's mixed-model equations, the tests can be performed without inverting the covariance matrix or computing a generalized inverse of the mixed-model coefficient matrix. The procedures are illustrated on an animal model that has three random effects, two with 1,372 levels and one with 450 levels.

Algorithms↗

PubMed1984

A linear theory for global electrocortical activity and its control by the lateral hypothalamus.

A linear model for electrocortical waves and their control by the lateral hypothalamus is proposed. It is argued that such a linear model is not in contradiction to non-linearity of neural elements on the microscopic scale. Telencephalic structures are treated as a mass of linked oscillators generating activity with a number of resonant modes. The lateral hypothalamus is regarded as controlling damping of activity in the telencephalic mass, and therefore exerting a specific parametric control over all signal processing in the cortical networks. An initial test is proposed to assess the constancy of telencephalic natural frequencies, with variation in lateral hypothalamic damping.

Animals↗

PubMed2000

Behavioral interventions reduce infant distress at immunization.

OBJECTIVE: To assess the effectiveness of simple behavioral interventions at immunization on behavioral and biochemical indicators of distress in infants and parents in a primary care setting. DESIGN: Subjects were enrolled sequentially to control (standard care) and intervention groups. Intervention parents (n=57) were provided information about techniques to help their infants at immunization. Standard care parents (n=45) did not receive this information. Immunizations were videotaped and coded for infant and parent behaviors. Using a visual analog scale, parents rated their infant's and their own comfort at study enrollment, immediately after immunization, and at check-out. Saliva samples collected from infants and parents at study enrollment and at 15, 30, and 60 minutes after immunization were assayed for cortisol concentration by standard radioimmunoassay. Data were analyzed using chi2, analysis of variance, and general linear modeling. Patterns of salivary cortisol change after immunization were analyzed using hierarchical linear modeling. SETTING: A single, urban pediatric practice during 2 summers (1997 and 1998). SUBJECTS: Infants 2 to 24 months of age (n= 102) and their parents. MAIN OUTCOME MEASURES: Duration of infant distress (in seconds); parent use of behavioral intervention; infant and parent salivary cortisol concentrations (in nanomoles per liter). RESULTS: Intervention parents were more likely to use a behavioral technique with their infants before immunization (P<.05). Total infant distress was shorter for intervention infants at immunization (P<.01), and these infants were rated as more comfortable by their parents (P<.001) immediately after immunization. Salivary cortisol levels were lower for intervention infants at 15, 30, and 60 minutes after immunization (P<.05). CONCLUSION: Simple behavioral interventions before immunization are associated with reductions in behavioral and biochemical indicators of infant distress.

Adaptation, Psychological↗

PubMed2004

Geographic distribution of environmental factors influencing human skin coloration.

Skin coloration in indigenous peoples is strongly related to levels of ultraviolet radiation (UVR). In this study, the relationships of skin reflectance to seasonal UVR levels and other environmental variables were investigated, with the aim of determining which variables contributed most significantly to skin reflectance. The UVR data recorded by satellite were combined with environmental variables and data on human skin reflectance in a geographic information system (GIS). These were then analyzed visually and statistically through exploratory data analysis, correlation analysis, principal components analysis, least-squares regression analysis, and nonlinear techniques. The main finding of this study was that the evolution of skin reflectance could be almost fully modeled as a linear effect of UVR in the autumn alone. This linear model needs only minor modification, by the introduction of terms for the maximum amount of UVR, and for summer precipitation and winter precipitation, to account for almost all the variation in skin reflectance. A further significant finding was that the effect of summer UVR seems to reach a threshold beyond which further adaptation is difficult.

Environmental Exposure↗

PubMed2001

Predicting quantitative trait levels by modeling SNP interaction.

Predicting phenotype from genotype is difficult when the phenotype is affected by a gene with numerous weakly penetrant alleles that differ only in the pattern of their single nucleotide polymorphisms (SNPs). While it is probable that SNP interactions affect phenotype, to our knowledge no one has determined the most effective way of evaluating whether SNPs interact and of modeling the interaction. Therefore, to explore this issue, we investigate here three methods of modeling SNP interaction using data from Genetic Analysis Workshop 12. Since major gene 5 (MG5) has sequence information and explains 37% of the variation in quantitative trait 5 (Q5), we focus on using SNPs within MG5 to predict Q5 among individuals who married into the pedigree. As a preliminary screening step, we reduced the number of SNPs from 269 to 34 based on their association with Q5. In our first models we assumed that SNPs affected Q5 in a simple additive manner. These models explained 34% and 15% of the variation in Q5 in women and men, respectively. Our second model was a linear model, which used individual SNPs and simple interaction terms as predictors. These models explained 36% and 16% of the variation in Q5 levels for women and men, respectively. Our last model was a "hit"-based model which was motivated by the hypothesis that disequilibrium between SNPs may reflect the fact that SNPs affect phenotype by acting in concert with other SNPs within their "disequilibrium set." Thus, the number of hits within the disequilibrium sets were used as predictors. These models explained 35% and 19% of the variation in Q5 for women and men, respectively. Our results suggest that phenotype can be predicted from complex patterns of weakly penetrant SNPs using relatively simple models. We concluded that SNP interaction either was not included in the simulation model, or had only a weak impact on Q5 levels.

Female↗

PubMed2006

Applying FSL to the FIAC data: model-based and model-free analysis of voice and sentence repetition priming.

This article presents results obtained from applying various tools from FSL (FMRIB Software Library) to data from the repetition priming experiment used for the HBM'05 Functional Image Analysis Contest. We present analyses from the model-based General Linear Model (GLM) tool (FEAT) and from the model-free independent component analysis tool (MELODIC). We also discuss the application of tools for the correction of image distortions prior to the statistical analysis and the utility of recent advances in functional magnetic resonance imaging (FMRI) time series modeling and inference such as the use of optimal constrained HRF basis function modeling and mixture modeling inference. The combination of hemodynamic response function (HRF) and mixture modeling, in particular, revealed that both sentence content and speaker voice priming effects occurred bilaterally along the length of the superior temporal sulcus (STS). These results suggest that both are processed in a single underlying system without any significant asymmetries for content vs. voice processing.

Brain Mapping↗

PubMed2007

Detecting functional nodes in large-scale cortical networks with functional magnetic resonance imaging: a principal component analysis of the human visual system.

This study aimed to demonstrate how a regional variant of principal component analysis (PCA) can be used to delineate the known functional subdivisions of the human visual system. Unlike conventional eigenimage analysis, PCA was carried out as a second-level analysis subsequent to model-based General Linear Model (GLM)-type functional activation mapping. Functional homogeneity of the functional magnetic resonance imaging (fMRI) time series within and between clusters was examined on several levels of the visual network, starting from the level of individual clusters up to the network level comprising two or more distinct visual regions. On each level, the number of significant components was identified and compared with the number of clusters in the data set. Eigenimages were used to examine the regional distribution of the extracted components. It was shown that voxels within individual clusters and voxels located in bilateral homologue visual regions can be represented by a single component, constituting the characteristic functional specialization of the cluster(s). If, however, PCA was applied to time series of voxels located in functionally distinct visual regions, more than one component was observed with each component being dominated by voxels in one of the investigated regions. The model of functional connections derived by PCA was in accordance with the well-known functional anatomy and anatomical connectivity of the visual system. PCA in combination with conventional activation mapping might therefore be used to identify the number of functionally distinct nodes in an fMRI data set in order to generate a model of functional connectivity within a neuroanatomical network.

Adult↗

PubMed2006

Disaster research methods: past progress and future directions.

Published results for 225 disaster studies were coded on methodological variables, severity of effects, and event year. Methods varied greatly, but cross-sectional, after-only designs, convenience sampling, and small samples were modal. Samples that were assessed before the disaster, selected for reasons of convenience, or were large tended to show less severe effects than other samples. Developing countries were underrepresented overall, but not in recent years. Certain desirable study characteristics (longitudinal designs, representative samples) have been decreasing in prevalence over time, whereas others (early first assessment) have been increasing. Innovations such as latent trajectory modeling or hierarchical linear modeling might advance the field's ability to capture the complexity of disasters, but the field still needs to attend to the fundamentals of sound epidemiologic research.

Data Interpretation, Statistical↗

PubMed2001

The applications of capture-recapture models to epidemiological data.

Capture-recapture methodology, originally developed for estimating demographic parameters of animal populations, has been applied to human populations. This tutorial reviews various closed capture-recapture models which are applicable to ascertainment data for estimating the size of a target population based on several incomplete lists of individuals. Most epidemiological approaches merging different lists and eliminating duplicate cases are likely to be biased downwards. That is, the final merged list misses those who are in the population but were not ascertained in any of the lists. If there are no matching errors, then the duplicate information collected from a capture-recapture experiment can be used to estimate the number of missed under proper assumptions. Three approaches and their associated estimation procedures are introduced: ecological models; log-linear models, and the sample coverage approach. Each approach has its unique way of incorporating two types of source dependencies: local (list) dependence and dependence due to heterogeneity. An interactive program, CARE (for capture-recapture) developed by the authors is demonstrated using four real data sets. One set of data deals with infection by the acute hepatitis A virus in an outbreak in Taiwan; the other three sets are ascertainment data on diabetes, spina bifida and infants' congenital anomaly discussed in the literature. These data sets provide examples to show the usefulness of the capture-recapture method in correcting for under-ascertainment. The limitations of the methodology and some cautionary remarks are also discussed.

Adult↗

PubMed1999

An experimental study of behavioural group size effects in tammar wallabies, Macropus eugenii.

As animals aggregate with others, the time they allot to social and nonsocial activities changes. Antipredator models of vigilance and foraging group size effects both predict a nonlinear relationship between group size and the time allocated to behaviour. Group size effects were experimentally studied in captive adult female tammar wallabies, a small macropodid marsupial, by increasing group size from 1 to 10. Tammars foraged more, looked less, groomed more, engaged in more aggressive interactions and moved about less as group size increased. Nonlinear regression models explained more variation in the time allocated to foraging, looking, locomotion and affiliative behaviour than linear models. Variation in self-grooming and aggression was better explained by linear models. Wallabies lay down significantly more, and walked significantly less, as group size increased: these relationships were significantly nonlinear. Thus, changes in perceived predation risk, which are characterized by nonlinear relationships, explain tammar wallaby group size effects for most activities. These results support the assertion that predation has played an important role in macropodid social evolution. Moreover, the findings suggest that conservation biologists should pay particular attention to group size when translocating or reintroducing endangered macropodids. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1988

EGF binding is quantitatively related to growth in node-positive breast cancer.

Number of mitoses and EGF binding were determined in parallel in biopsies of 27 lymph-node positive and of 23 lymph-node negative breast cancer patients. For node-positive patients the parameters for cell growth and EGF binding were quantitatively correlated by the equation y = P3 + P1(1- exp(- P2x]. For node-negative cases neither the non-linear model nor the linear approximation described the data unambiguously. The results strongly suggest that in node-positive patients, growth of breast cancer is related to an EGF-dependent acceleration of cell division.

Adult↗

PubMed2006

Predictive controller evaluation including non-stationary high frequency noise and outliers for batch solid substrate fermentation bioreactors.

Optimum operation and automatic control of large-scale solid substrate fermentation (SSF) bioreactors is difficult. Though advanced control algorithms can handle most challenges encountered properly, for real-time SSF processes such controllers are expensive and time consuming to design and tune. With these considerations, advanced control algorithm tests using realistic simulations appear more appropriate. We used a phenomenological process model of an SSF pilot bioreactor, coupled with a realistic noise model, to test linear model predictive controllers. We focused on the effect noise has on the performance of the control algorithms, and how to enhance performance using a combination of low-pass (Butterworth) and outlier shaving (Hampel) filters. In simulations undertaken directly with the phenomenological model it was relatively straightforward to achieve good control performance. Nevertheless, control degraded sharply when the output of the phenomenological model was contaminated with noise using our realistic noise model, even with proper signal filtering.

Artifacts↗

PubMed2006

A rapid method for assessing the environmental performance of commercial farms in the Pampas of Argentina.

The generation of reliable updated information is critical to support the harmonization of socio-economic and environmental issues in a context of sustainable development. The agro-environmental assessment and management of agricultural systems often relies on indicators that are necessary to make sound decisions. This work aims to provide an approach to (a) assess the environmental performance of commercial farms in the Pampas of Argentina, and (b) propose a methodological framework to calculate environmental indicators that can rapidly be applied to practical farming. 120 commercial farms scattered across the Pampas were analyzed in this study during 2002 and 2003. Eleven basic indicators were identified and calculation methods described. Such indicators were fossil energy (FE) use, FE use efficiency, nitrogen (N) balance, phosphorus (P) balance, N contamination risk, P contamination risk, pesticide contamination risk, soil erosion risk, habitat intervention, changes in soil carbon stock, and balance of greenhouse gases. A model named Agro-Eco-Index was developed on a Microsoft-Excel support to incorporate on-farm collected data and facilitate the calculation of indicators by users. Different procedures were applied to validate the model and present the results to the users. Regression models (based on linear and non-linear models) were used to validate the comparative performance of the study farms across the Pampas. An environmental dashboard was provided to represent in a graphical way the behavior of farms. The method provides a tool to discriminate environmentally friendly farms from those that do not pay enough attention to environmental issues. Our procedure might be useful for implementing an ecological certification system to reward a good environmental behavior in society (e.g., through tax benefits) and generate a commercial advantage (e.g., through the allocation of green labels) for committed farmers.

Agriculture↗

PubMed1994

Patterns and temporal trends in the incidence of malignant disease in children: I. Leukaemia and lymphoma.

Patterns and trends in incidence of leukaemia and lymphoma in children aged under 15 years and resident in the North Western Regional Health Authority area of England at diagnosis, over the 35-year time period 1954-1988, were analysed. The study included 1407 cases registered with the Manchester Children's Tumour Registry, 100% of which had a histologically or cytologically verified diagnosis. Log-linear modelling identified significant linear increases in acute lymphocytic leukaemia (ALL) (average quinquennial increase 4%) and Hodgkin's disease (HD) (10%), but not in acute non-lymphocytic leukaemia nor non-Hodgkin's lymphoma. Additionally, the chi 2 test for trend identified a significant increase in the incidence of chronic myeloid leukaemia. The possibility that the increases seen in ALL and HD are linked to increases in prevalence of unknown infectious agents is discussed.

Adolescent↗