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PubMed2004

Testing for common structures in a panel of threshold models.

We consider the problem of examining the extent of (partial) similarity in the dynamics of a panel of independent threshold autoregressive processes. We develop some tests for common structure via Wald's approach and by checking whether the parameter estimates of the unconstrained threshold models satisfy the constraints defining the common structure. One test concerns the equality of independent ratios of normal means, which is shown to have nonstandard asymptotic null distribution. These tests are illustrated with a modern panel of Canadian lynx data; our analysis suggests that the lynx data over Canada share similar dynamics in the decrease phase, but they appear to be different in the increase phase.

Animals↗

PubMed1992

A new four-parameter threshold model for the plasma atracurium concentration-response relationship.

The plasma concentration of atracurium and the electromyographic depression of the first response of the train-of-four (T1:T0) were measured during and after recovery from a 10-min infusion of atracurium 0.25 mg kg-1 in 14 patients anaesthetized with 66% nitrous oxide and 0.9% isoflurane (end-tidal) in oxygen. A standard pharmaco-dynamic model was fitted to the data; a small but consistent discrepancy was found between the time and rate of onset of depression of the ratio T1:T0 and the predictions of the standard biophase model of best fit to the data. This discrepancy is reduced by the inclusion of a threshold term (CPss theta) in the model to represent the greatest steady state plasma concentration which would just fail to evoke an effect. The values of CPss theta correlated significantly with the values of CPss50 (r = +0.627; P less than 0.02). The estimates of CPss50 and keo from the two models are very similar; the estimate of gamma, the slope of the concentration-response curve, was less in the threshold model. The relationship of the present threshold model to existing knowledge of neuromuscular physiology is discussed.

Adult↗

PubMed1996

Caregiver training for people with Alzheimer's based on a stress threshold model.

A caregiver training protocol for Alzheimer's disease and related disorders (ADRD) is presented for dementia management based on the progressively lowered stress threshold model. The training protocol is described using criteria for a nursing intervention including: (a) characteristics of the nursing diagnosis, (b) research base for the intervention, (c) desired patient outcomes, (d) acceptability to the patient, (e) capability of the nurse, and (f) feasibility for doing the intervention. A national study is described which is currently underway to further evaluate the effects of the training protocol.

Alzheimer Disease↗

PubMed2002

Predicting the presence of acute pulmonary embolism: a comparative analysis of the artificial neural network, logistic regression, and threshold models.

OBJECTIVE: The objective of this study was to determine whether an artificial neural network, a new data analysis method, offers increased performance over conventional logistic regression in predicting the presence of a pulmonary embolism for patients in a well-known data set. MATERIALS AND METHODS: Data from the 1064 patients who received an angiographically based diagnosis of pulmonary embolism in the Prospective Investigation of Pulmonary Embolism Diagnosis study were encoded using a previously described method. The 21 input variables represented abnormalities identified on each patient's ventilation-perfusion scan and chest radiograph. Two methods-an artificial neural network with one hidden layer and a multivariate logistic regression-were compared for accuracy in predicting the presence or absence of pulmonary embolism on subsequent pulmonary arteriography. RESULTS: No significant difference was observed between the two methods. Areas under the receiver operating characteristic curves +/- standard deviation were 0.78 +/- 0.02 for the artificial neural network model and 0.79 +/- 0.02 for the logistic regression model. Furthermore, use of these two methods resulted in no more diagnostic accuracy than did the use of a simple threshold model based only on the number of subsegmental perfusion defects, which was the dominant input variable. CONCLUSION: In the study population, the usefulness of data from ventilation-perfusion scans as predictors of the presence of a pulmonary embolism was similar for the three analytic methods, a finding that reinforces the importance of making comparisons to simpler or more established methods when performing studies involving complex analytic models, such as artificial neural networks.

Acute Disease↗

PubMed2000

Threshold Models for Comparative Probability on Finite Sets.

Let succeeds be a comparative probability relation on the set &Bscr;(S) of all subsets of a finite state space S. This paper presents and discusses necessary and sufficient axioms for several threshold models of succeeds, whose general representational form yields a probability measure P on &Bscr;(S) and a bivariate set function Omega>/=0 on &Bscr;(S)x&Bscr;(S) such that for all A, Bin&Bscr;(S), A succeedsB if and only if P(A)>P(B)+Omega(A, B). Several conditions such as skew-monotonicity and additive separability will be imposed on the functional form of Omega. Copyright 2000 Academic Press.

Journal Article↗

PubMed1996

The gradual threshold model of ambivalence: relating the positive and negative bases of attitudes to subjective ambivalence.

This research examined the relationship between the measured (Study 1) and manipulated (Studies 2 and 3) positive and negative bases of attitudes and the psychological experience of attitudinal ambivalence. On the basis of these studies, the gradual threshold model of ambivalence (GTM) was advanced. The GTM holds that: (a) ambivalence increases in a negatively accelerating manner as the number of conflicting reactions (whichever of the positive or negative reactions are fewer in number) increases, (b) ambivalence is a negative function of the extent of dominant reactions, and (c) as the number of conflicting reactions increases, the impact of dominant reactions on ambivalence gradually decreases such that at some level of conflicting reactions (i.e, the threshold), the number of dominant reactions no longer has an impact on subjective ambivalence.

Adult↗

PubMed2001

The threshold model as a general purpose normalizing transformation.

The estimation of heritabilities and genetic correlations is based on the assumption that the trait distributions are normal. When the distributions are not normal it is advisable to transform the data to produce normality. However, it is possible that no suitable transformation can be found. The purpose of the present paper is to point out that the threshold model of quantitative genetics can be used as a generalized transformation. To utilize this method it is only necessary to divide the data at the median (approximately) and code the two halves as 0 and 1. Estimates can then be made using algorithms outlined herein. A simulation study shows that the threshold transformation gave unbiased estimates of the heritability and genetic correlation in all cases. The 95% confidence limits correctly included the true heritability value in the required 95% of cases, while the estimated confidence region for the genetic correlation was also correct provided that the geometric mean heritability was greater than approximately 0.15, a restriction that applied also to the normally distributed data. Confidence intervals estimated from the non-normal data were consistently too small. The method is illustrated using data on the proportion of diapausing eggs produced by the cricket, Allonemobius socius.

Animals↗

PubMed1981

Confirmation of the multifactorial threshold model for congenital structural talipes equinovarus.

The first degree relatives of 174 children with congenital isolated structural talipes equinovarus were examined by an orthopaedic surgeon. The affected rate of first degree relatives was 27 times higher than the birth prevalence of Hungarian newborns. The heritability in the parents and sibs was 0.82 +/- 0.15. The multifactorial threshold model was proved by the so-called GAMT programme on the basis of the identity of the h2 values in the different generations of first degree relatives. A relatively lower familial clustering was found in gypsies who had a higher prevalence.

Clubfoot↗

PubMed1993

Evaluating a speech-reception threshold model for hearing-impaired listeners.

Plomp's speech reception threshold (SRT) model [R. Plomp, J. Acoust. Soc. Am. 63, 533-549 (1978)] incorporates a distortion and an attenuation factor that are both expressed in dB and, for hearing-impaired listeners, are greater than 0 dB. The distortion factor is hypothesized to affect the SRT in quiet and in noise and suggests that a hearing-impaired listener will always demonstrate a higher SRT than a normal-hearing listener. The present study examines whether this distortion factor can be explained for many listeners simply by inaudibility of a portion of the speech spectrum. SRTs were obtained from normal-hearing and mild-to-moderately hearing-impaired listeners in quiet and at various noise levels. The results indicate that, at high noise levels, when the noise, rather than the quiet threshold, becomes the dominating factor, the SRT functions of both the normal and the mild-to-moderately hearing-impaired group converge and the distortion factor diminishes to zero. Predictions were also made using an articulation index and similar convergence of the two functions was observed.

Acoustic Stimulation↗

PubMed1996

Threshold models in a methadone programme evaluation.

The degree of non-compliance with a methadone programme is such that a zero is often recorded as the response variable. Such outcome variables cannot be transformed to normality in order to investigate a regression relationship between the response variable and various risk or treatment variables. The presence of a random effect as well in this regression causes added difficulty in the analysis. We show here that use of threshold models can provide a satisfactory solution to both these problems.

Australia↗

PubMed1991

A new method for the analysis of the dynamics of the molecular genetic control systems. I. Description of the method of generalized threshold models.

In the molecular system of coding polymers and metabolites a control subsystem has been singled out that forms controlling variables showing the action of regulatory molecules and a controlled subsystem where, depending on the values of controlling variables controlled variables are formed, i.e. concentrations of DNA, m-RNA, proteins and metabolites. Relationships have been obtained which enable controlling variables to be found. Equations showing the dynamics of molecular genetic control systems' components have been obtained. A method of generalized threshold models that enables kinetic curves to be obtained by pure mathematical means for macromolecular components (DNA, RNA, proteins) of molecular genetic control systems of varying complexity is suggested.

Animals↗

PubMed1986

A multidimensional threshold model for multiple congenital abnormalities.

Analysis of the data of 2.762 infants with "unidentified" (i.e., no identified as dysmorphological entities) multiple congenital abnormalities from the Hungarian Congenital Malformation Registry, 1970-1976 showed that the majority of congenital abnormalities in newborns with multiple congenital abnormalities was not due to random combinations. The ratio of expected random combination and observed causal effect was 1: 6, 1: 225-1: 14,000 and 1: 2.10(6) in two, three, four, and five or more congenital abnormalities, respectively. Our multidimensional threshold model supposes specified liabilities for each congenital abnormality, and the correlation structure of these liabilities explains nearly all associations of congenital abnormalities in unidentified multiple congenital abnormalities. According to this hypothesis, the expected and the observed occurrences do not differ significantly either in the sum or in the various possible threefold associations of congenital abnormalities. The biological reasons for the phenomenon are being studied.

Abnormalities, Multiple↗

PubMed1997

Cluster analytic validation of the DSM melancholic depression. The threshold model: integration of quantitative and qualitative distinctions between unipolar depressive subtypes.

Cluster analysis was performed on the DSM-III symptoms of major depression and symptoms of melancholia identified in a study group consisting of 220 unipolar depressed inpatients a melancholic and non-melancholic cluster. Patients allocated to the melancholic cluster were more severely depressed and they were characterized by psychomotor disorders, a distinct quality of mood, diurnal variation, early morning awakening, and non-reactivity. Our results support the construct validity of the DSM-III melancholic subtype of major depression. This study supports the integrated threshold model:. (i) melancholic and non-melancholic depression may be regarded as continuous classes in terms of overall severity of depression; and (ii) both groups form discrete categories with regard to the melancholic symptoms, which emerge as the severity of depression increases.

Adjustment Disorders↗

PubMed1994

Logistic regression analysis of twin data: estimation of parameters of the multifactorial liability-threshold model.

We extend the DeFries-Fulker regression model for the analysis of quantitative twin data to cover binary traits and genetic dominance. In the proposed logistic regression model, the cotwin's trait status, C, is the response variable, while the proband's trait status, P, is a predictor variable coded as k (affected) and 0 (unaffected). Additive genetic effects are modeled by the predictor variable PR, which equals P for monozygotic (MZ) and P/2 for dizygotic (DZ) twins; and dominant genetic effects, by PD, which equals P for MZ and P/4 for DZ twins. By setting an appropriate scale for P (i.e., the value of k), the regression coefficients of P, PR, and PD are estimates of the proportion of variance in liability due to common family environment, additive genetic effects, and dominant genetic effects, respectively, for a multifactorial liability-threshold model. This model was applied to data on lifetime depression from the Virginia Twin Registry and produced results similar to those from structural equation modeling.

Adult↗

PubMed1998

Context-dependent nestmate discrimination in the paper wasp, Polistes dominulus: a critical test of the optimal acceptance threshold model.

e present evidence that nestmate discrimination in the eusocial paper wasp, Polistes dominulus, is context dependent. We compared aggression levels between nestmates and non-nestmates in dyads consisting of a pair of either nestmates or non-nestmates, and triads consisting of either three nestmates, three non-nestmates, or two nestmates and a non-nestmate. In 130 of the 237 total trials, a nest fragment (containing both brood and eggs) from the nest of some, all or none of the interactants was placed into the interaction arena. Polistes dominulus workers recognized and discriminated nestmates from non-nestmates, familiar from unfamiliar nest material and neighbours from non-neighbours. These findings suggest that nestmate and neighbour discrimination are context dependent: discrimination occurs when either the presence of a nestmate or a familiar nest fragment indicate the proximity of the colony. The context-dependent variation in aggression levels is best described by multiple, context-dependent shifts in an acceptance threshold. Thus this study provides the most extensive, critical support yet obtained for Reeve's (1989, American Naturalist, 133, 407-435) optimal acceptance threshold model. Copyright 1998 The Association for the Study of Animal Behaviour

Journal Article↗

PubMed2002

Regulation of WNT signaling molecules by retinoic acid during neuronal differentiation in NT2 cells: threshold model of WNT action (review).

NT2/NTera2 cells, derived from human embryonal tumor, differentiate into neuronal cells after treatment with all-trans-retinoic acid (ATRA). We have cloned and characterized 13 out of 19 human WNT genes, and also 9 out of 10 human Frizzled (FZD) genes encoding seven-transmembrane-type WNT receptors, which are potent targets for pharmacogenomics in the post-genomic era, especially in the field of regenerative medicine and clinical oncology. Because WNT signals are implicated in morphogenesis of neural tissues, regulation of 19 WNT genes and 10 FZD genes during the early phase of neuronal differentiation in NT2 cells is reviewed. Multiple WNTs and FZDs are expressed in NT2 cells. WNT2B/WNT13 gene encode 2 isoforms due to alternative splicing of alternative promoter type, and WNT2B isoform 2 (WNT2B2) rather than WNT2B isoform 1 (WNT2B1) is expressed in NT2 cells. WNT3A, WNT8A, WNT8B, WNT10B and WNT11 are down-regulated in NT2 cells after ATRA treatment, while WNT2, WNT7B and WNT14B are up-regulated. FZD4 and FZD10 are up-regulated in NT2 cells after ATRA treatment. Expression of multiple WNT signaling molecules are dramatically changed during the early phase of neuronal differentiation in NT2 cells. Each WNT activates the beta-catenin - TCF pathway, the JNK pathway or the Ca2+-releasing pathway in NT2 cells, and summed effects of multiple WNTs might determine the fate of NT2 cells (self-renewal or differentiation) through switching intracellular WNT signaling pathways. The author proposes the threshold model of WNT action.

Cell Differentiation↗

PubMed2002

Measurement of excitability of tonically firing neurones tested in a variable-threshold model motoneurone.

A new measure of excitability of tonically firing neurones termed the 'estimated potential' (EP) was tested on a model motoneurone (MN) with a voltage-dependent threshold; the threshold followed the noisy membrane potential with an exponential delay. First, the model MN's after-hyperpolarisation (AHP) was deduced from its interval histogram for tonic firing, using a recently described transform. This provided a 'distance-to-threshold' measure which underestimated the AHP's absolute size but had the same time course, thereby providing the time constant of the AHP's decay of conductance. The 'estimated potential' was then obtained from the classical 'firing index' (no. of responses/no. of stimuli) by using the estimated AHP to create a fixed threshold 'daughter' model MN to mimic its variable threshold parent and reproduce its input-output non-linearities. The EP gave a linear measure of the parent's stimulus-evoked depolarisation for firing indices up to about 60 %, corresponding to depolarisations of three to four times the noise S.D. The EP was scaled in units of voltage whose absolute value will usually be unknown for real neurones, since it depended upon the details of the parent model. The EP's virtue is that, within its range, combining stimuli gives arithmetical addition and subtraction, thereby improving on the firing index which scales sigmoidally with the input. Moreover, with weak stimuli, the EP for a given input did not change on varying the parent model's firing rate. The estimated 'distance-to-threshold' AHP did not, however, give an accurate measure of the recovery of excitability following a spike during tonic firing. Excitability then depends upon the 'survivors' trajectory' giving the mean membrane potential, relative to threshold, of those intervals which have 'survived' up to the time in question rather than upon the AHP per se; the survivors' mean is more hyperpolarised because spiking preferentially eliminates trajectories with noise-induced depolarisation.

Animals↗

PubMedDate not supplied

Relatedness of schizotypal personality to schizophrenic disorders: multifactorial threshold model.

Genetic analysis of schizophrenia and schizotypal personality disorder (SPD) was conducted on two pedigree samples. The results are interpreted in terms of a multifactorial threshold (MFT) model. A high rate of schizophrenia was found in relatives of both samples, but any excess of SPD was found only in relatives of the SPD sample. Based on these data, the hypotheses assuming a single liability with two thresholds (Reich's model) and different liability (Smith's model) for both disorders were rejected. The coefficient of genetic correlation is 0.61. Our data suggest that schizophrenia and SPD are separate nosological entities and that some of the factors which constitute liability to SPD influence the development of schizophrenia, but not vice versa.

Adolescent↗