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Robin Thompson

Publications and source records attributed to Robin Thompson.

14 recordsLinked to original sources
PubMed2006

The analysis of longitudinal data using mixed model L-splines.

L-splines are a large family of smoothing splines defined in terms of a linear differential operator. This article develops L-splines within the context of linear mixed models and uses the resulting mixed model L-spline to analyze longitudinal data from a grassland experiment. In the spirit of time-series analysis, a periodic mixed model L-spline is developed, which partitions data into a smooth periodic component plus smooth long-term trend.

Biomass↗
PubMed2005

Estimation of quantitative genetic parameters.

This paper gives a short review of the development of genetic parameter estimation over the last 40 years. This shows the development of more statistically and computationally efficient methods that allow the fitting of more biologically appropriate models. Methods have evolved from direct methods based on covariances between relatives to methods based on individual animal models. Maximum-likelihood methods have a natural interpretation in terms of best linear unbiased predictors. Improvements in iterative schemes to give estimates are discussed. As an example, a recent estimation of genetic parameters for a British population of dairy cattle is discussed. The development makes a connection to relevant work by Bill Hill.

Analysis of Variance↗
PubMed2005

"Tip of the fingers" experiences by deaf signers: insights into the organization of a sign-based lexicon.

The "tip of the fingers" phenomenon (TOF) for sign language parallels the "tip of the tongue" phenomenon (TOT) for spoken language. During a TOF, signers are sure they know a sign but cannot retrieve it. Although some theories collapse semantics and phonology in sign language and thus predict that TOFs should not occur, TOFs were elicited in the current study. Like TOTs, TOFs often resolve spontaneously, commonly involve targets that are proper names, and frequently include partial access to phonology. Specifically, signers were more likely to retrieve a target sign's handshape, location, and orientation than to retrieve its movement. Signers also frequently recalled the first letter of a finger-spelled word. The existence of TOFs supports two-stage retrieval and a division between semantics and phonology in American Sign Language. The partial phonological information available during TOFs suggests that phonological features are accessed more simultaneously during lexical access for signed language than during lexical access for spoken language.

Adult↗
PubMed2004

Multivariate character process models for the analysis of two or more correlated function-valued traits.

Various methods, including random regression, structured antedependence models, and character process models, have been proposed for the genetic analysis of longitudinal data and other function-valued traits. For univariate problems, the character process models have been shown to perform well in comparison to alternative methods. The aim of this article is to present an extension of these models to the simultaneous analysis of two or more correlated function-valued traits. Analytical forms for stationary and nonstationary cross-covariance functions are studied. Comparisons with the other approaches are presented in a simulation study and in an example of a bivariate analysis of genetic covariance in age-specific fecundity and mortality in Drosophila. As in the univariate case, bivariate character process models with an exponential correlation were found to be quite close to first-order structured antedependence models. The simulation study showed that the choice of the most appropriate methodology is highly dependent on the covariance structure of the data. The bivariate character process approach proved to be able to deal with quite complex nonstationary and nonsymmetric cross-correlation structures and was found to be the most appropriate for the real data example of the fruit fly Drosophila melanogaster.

Age Factors↗
PubMed2003

Health-seeking behaviour and rural/urban variation in Kazakhstan.

This paper seeks to analyse the findings of an extensive household survey, uncovering interesting evidence of variation in health-seeking behaviour across rural and urban areas due, it is suggested, to differences in real costs, quality of care, and perceptions of the value of health and health care. It is shown that, ceteris paribus, urban households in Kazakhstan are more likely to consult, to be admitted to hospital, to report illness, and will spend relatively more on health care. The data suggest the need for further qualitative study into the factors underlying these patterns leading to strategies to increase the quality, acceptability and affordability of rural health services. This is important given the decline in health indicators such as life expectancy in Kazakhstan and the increased burden on households of funding health care in a time of economic insecurity and deterioration of public services.

Adult↗
PubMed2003

Variation in response to neonicotinoid insecticides in peach-potato aphids, Myzus persicae (Hemiptera: Aphididae).

Laboratory bioassays applying the neonicotinoid insecticides imidacloprid, acetamiprid and nitenpyram against clones of the peach-potato aphid Myzus persicae (Sulzer) demonstrated that these compounds effectively circumvent the known carboxylesterase, modified acetylcholinesterase (MACE) and knock-down (kdr) insecticide resistance mechanisms in this species. However, some clones showed cross-tolerance (up to 18-fold) of these compounds relative to susceptible standards. A survey assessing the frequency of neonicotinoid tolerance in M persicae in the UK, based on samples collected from the field and glasshouses between 1997 and 2000, showed that such tolerance is still rare. Experiments on neonicotinoid-susceptible and -tolerant populations of M persicae under simulated field conditions in the laboratory showed that, although the latter were well controlled by imidacloprid applied at recommended application rates, they were more likely to survive and reproduce when this compound was applied at lower concentrations. Such conditions are probably periodically present in imidacloprid-treated field and glasshouse crops. Selection favouring tolerant forms of M persicae could lead to increases in their frequency and the evolution of more potent resistance to neonicotinoids.

Anabasine↗
PubMed2003

Association of MACE-based insecticide resistance in Myzus persicae with reproductive rate, response to alarm pheromone and vulnerability to attack by Aphidius colemani.

Reproductive success and response to alarm pheromone, both potentially important components of fitness, were assessed using clones of Myzus persicae (Sulzer) to establish associations with insecticide resistance conferred by insensitive modified acetylcholinesterase (MACE). Both traits showed significant trends that were apparently related to this mechanism. MACE forms appeared to reproduce at slower rates than non-MACE forms expressing moderate (R1) levels of another resistance mechanism based on elevated carboxylesterase. However, MACE forms were more responsive to alarm pheromone than their non-MACE counterparts. The potential implications for parasitoid performance were tested using two clones showing clear differences in alarm response. The level of parasitism of M persicae by the parasitoid Aphidius colemani (Viereck) was significantly lower in MACE forms on pepper crops compared to non-MACE forms. In addition, the distribution of MACE and non-MACE forms differed on the pepper plants, with more MACE forms being found on the growing points. The presence of the parasitoid A colemani did not alter this change in distribution.

Acetylcholinesterase↗
PubMed2003

Structured antedependence models for genetic analysis of repeated measures on multiple quantitative traits.

Simultaneous analysis of correlated traits that change with time is an important issue in genetic analyses. Several methodologies have already been proposed for the genetic analysis of longitudinal data on single traits, in particular random regression and character process models. Although the latter proved, in most cases, to compare favourably to alternative approaches for analysis of single function-valued traits, they do not allow a straightforward extension to the multivariate case. In this paper, another methodology (structured antedependence models) is proposed, and methods are derived for the genetic analysis of two or more correlated function-valued traits. Multivariate analyses are presented of fertility and mortality in Drosophila and of milk, fat and protein yields in dairy cattle. These models offer a substantial flexibility for the correlation structure, even in the case of complex non-stationary patterns, and perform better than multivariate random regression models, with fewer parameters.

Animals↗
PubMed2003

Trichuris suis seems to be safe and possibly effective in the treatment of inflammatory bowel disease.

OBJECTIVES: Inflammatory bowel disease (IBD), especially Crohn's disease (CD), probably results from failure to downregulate a chronic Th1 intestinal inflammatory process. Induction of a Th2 immune response by intestinal helminths diminishes Th1 responsiveness. This study evaluates the safety and effectiveness of helminthic ova in the treatment of active IBD. METHODS: We studied four patients with active CD and three with ulcerative colitis (UC). In an initial treatment and observation period, a single dose of 2500 live Trichuris suis eggs was given orally, and patients were followed every 2 wk for 12 wk. Baseline medications were continued at the same dose throughout the study. Safety was monitored by following the patients' clinical status and laboratory studies at regular intervals. Patients also were monitored regularly using the Crohn's Disease Activity Index, Simple Clinical Colitis Activity Index (SCCAI), and the Inflammatory Bowel Disease Quality of Life Index (IBDQ). To assess safety and efficacy with repetitive doses, two patients with CD and two with UC were given 2500 ova at 3-wk intervals as maintenance treatment using the same evaluation parameters. RESULTS: During the treatment and observation period, all patients improved clinically without any adverse clinical events or laboratory abnormalities. Three of the four patients with CD entered remission according to the Crohn's Disease Activity Index; the fourth patient experienced a clinical response (reduction of 151) but did not achieve remission. Patients with UC experienced a reduction of the Clinical Colitis Activity Index to 57% of baseline. According to the IBD Quality of Life Index, six of seven patients (86%) achieved remission. The benefit derived from the initial dose was temporary. In the maintenance period, multiple doses again caused no adverse effects and sustained clinical improvement in all patients treated every 3 wk for >28 wk. CONCLUSIONS: This open trial demonstrates that it is safe to administer eggs from the porcine whipworm, Trichuris suis, to patients with CD and UC. It also demonstrates improvement in the common clinical indices used to describe disease activity. The benefit was temporary in some patients with a single dose, but it could be prolonged with maintenance therapy every 3 wk. The study suggests that it is possible to downregulate aberrant intestinal inflammation in humans with helminths.

Administration, Oral↗
PubMed2002

Bioassay and field-simulator studies of the efficacy of pymetrozine against peach-potato aphids, Myzus persicae (Hemiptera: Aphididae), possessing different mechanisms of insecticide resistance.

Twenty-one clones of the peach-potato aphid, Myzus persicae (Sulzer), carrying various combinations of known mechanisms of insecticide resistance were assessed for their response to the new pyridine azomethine compound, pymetrozine, in leaf-dip bioassays. Pymetrozine was also applied as a foliar spray to populations of four different UK M persicae clones on potato plants in field-simulator chambers. Neither study showed any evidence of cross-resistance to this compound. Pymetrozine, used in conjunction with other effective aphicides, such as pirimicarb and imidacloprid, can therefore play an important role in insecticide resistance-management strategies for M persicae.

Animals↗
PubMed2002

On the mapping of quantitative trait loci at marker and non-marker locations.

Previous studies have noted that the estimated positions of a large proportion of mapped quantitative trait loci (QTLs) coincide with marker locations and have suggested that this indicates a bias in the mapping methodology. In this study we predict the expected proportion of QTLs with positions estimated to be at the location of a marker and further examine the problem using simulated data. The results show that the higher proportion of putative QTLs estimated to be at marker positions compared with non-marker positions is an expected consequence of the estimation methods. The study initially focused on a single interval with no QTLs and was extended to include multiple intervals and QTLs of large effect. Further, the study demonstrated that the larger proportion of estimated QTL positions at the location of markers was not unique to linear regression mapping. Maximum likelihood produced similar results, although the accumulation of positional estimates at outermost markers was reduced when regions outside the linkage group were also considered. The bias towards marker positions is greatest under the null hypothesis of no QTLs or when QTL effects are small. This study discusses the impact the findings could have on the calculation of thresholds and confidence intervals produced by bootstrap methods.

Animals↗
PubMedDate not supplied

Use of the score test as a goodness-of-fit measure of the covariance structure in genetic analysis of longitudinal data.

Model selection is an essential issue in longitudinal data analysis since many different models have been proposed to fit the covariance structure. The likelihood criterion is commonly used and allows to compare the fit of alternative models. Its value does not reflect, however, the potential improvement that can still be reached in fitting the data unless a reference model with the actual covariance structure is available. The score test approach does not require the knowledge of a reference model, and the score statistic has a meaningful interpretation in itself as a goodness-of-fit measure. The aim of this paper was to show how the score statistic may be separated into the genetic and environmental parts, which is difficult with the likelihood criterion, and how it can be used to check parametric assumptions made on variance and correlation parameters. Selection of models for genetic analysis was applied to a dairy cattle example for milk production.

Animals↗