Biomedical subjects

E Lesaffre

Publications and source records attributed to E Lesaffre.

114 records · Page 7Linked to original sources

PubMedDate not supplied

Marginal modelling of multivariate categorical data.

This paper describes likelihood methods of analysis for multivariate categorical data. The joint distribution is specified in terms of marginal mean functions, and pairwise and higher order association measures. For the association, the emphasis is on global odds ratios. The method allows flexible formulation of a broad class of designs, such as repeated measurements, longitudinal studies, interrater agreement and cross-over trials. The proposed model can be used for parameter estimation and hypothesis testing. Simple fitting algorithms are proposed. The method is illustrated using a data example.

Adolescent↗

PubMedDate not supplied

Missing data perspectives of the fluvoxamine data set: a review.

Fitting models to incomplete categorical data requires more care than fitting models to the complete data counterparts, not only in the setting of missing data that are non-randomly missing, but even in the familiar missing at random setting. Various aspects of this point of view have been considered in the literature. We review it using data from a multi-centre trial on the relief of psychiatric symptoms. First, it is shown how the usual expected information matrix (referred to as naive information) is biased even under a missing at random mechanism. Second, issues that arise under non-random missingness assumptions are illustrated. It is argued that at least some of these problems can be avoided using contextual information.

Data Interpretation, Statistical↗

PubMedDate not supplied

Disease mapping models: an empirical evaluation. Disease Mapping Collaborative Group.

The analysis of small area disease incidence has now developed to a degree where many methods have been proposed. However, there are few studies of the relative merits of the methods available. While many Bayesian models have been examined with respect to prior sensitivity, it is clear that wider comparisons of methods are largely missing from the literature. In this paper we present some preliminary results concerning the goodness-of-fit of a variety of disease mapping methods to simulated data for disease incidence derived from a range of models. These simulated models cover simple risk gradients to more complex true risk structures, including spatial correlation. The main general results presented here show that the gamma-Poisson exchangeable model and the Besag, York and Mollie (BYM) model are most robust across a range of diverse models. Mixture models are less robust. Non-parametric smoothing methods perform badly in general. Linear Bayes methods display behaviour similar to that of the gamma-Poisson methods.

Algorithms↗

PubMedDate not supplied

Determinants of infarct size in non-human primates.

To achieve a better understanding of the major factors that determine infarct size in non-human primates, a mathematical model was constructed using stepwise regression analysis. The model was developed on the basis of infarct size measurements, including the anatomical area at risk, regional myocardial blood flow measurements and hemodynamic determinants obtained in 23 control baboons undergoing up to 2 h of coronary artery thrombosis followed by thrombolysis. In this model, the size of the perfusion bed of the occluded coronary artery and the duration of coronary artery occlusion were found to be the only important predictors of infarct size (expressed as a percentage of left ventricular mass). R2 (square or the multiple correlation coefficient) was 70% in this model. Collateral blood flow and rate-pressure product were not identified as important predictors of infarct size. In a second group of eight baboons, atenolol (0.1 mg.kg-1) was administered intravenously 15 min after the onset of coronary artery thrombosis. Predicted infarct size (based on the mathematical model obtained in the control group) was larger than the observed infarct size in seven out of eight cases. In four instances observed infarct size was smaller than the 95% lower limit of the predicted value. It is concluded that the determinants of infarct size in non-human primates differ from those in canine models with respect to collateral flow and estimates of myocardial oxygen consumption (rate pressure product). The developed mathematical model of infarct size prediction allows the detection of cardioprotective drug effects with an acceptable efficacy.

Animals↗

PubMedDate not supplied

The value of a baseline caries risk assessment model in the primary dentition for the prediction of caries incidence in the permanent dentition.

To establish a reliable screening method for caries prediction and to identify predominant risk factors, this study tested whether a cross-sectional caries risk model assessed at age 7 could be used to predict future caries onset in the permanent first molars at age 10 in 3,303 children born in 1989. As prediction variables, assessing the believed risk, baseline data at age 7 on oral health status, oral hygiene level, oral health behaviour and sociodemographic factors were used. The real risk, based on data collected for the first permanent molars during the follow-up, was assessed by different approaches. Cumulative incidence during the 3-year observation period was 31.6%, ranging from 22.4% in the believed low-risk group to 43.2% in the believed high-risk group. A stepwise logistic regression analysis was performed with net caries increment as outcome measure, adjusted for the real time at risk, using eruption times. Baseline dmfs and occlusal and buccal plaque indices were highly significant for having a high caries increment in permanent first molars with respective odds ratios of 1.07, 1.43 and 1.35. Brushing less than once a day and the daily use of sugar-containing drinks between meals were confirmed as risk factors (OR 2.43 and 1.25, respectively). The logistic regression analysis provided a sensitivity of 59-66% and a specificity of 65.7-72.8%, which indicates that the risk marker did not have an important predictive power. None of the socio-demographic and behavioural variables had enough predictive power at community level to be useful for identifying caries susceptible children. Even the power of dmfs at baseline must be considered modest.

Beverages↗

PubMedDate not supplied

Effect of caries experience in primary molars on cavity formation in the adjacent permanent first molar.

This study sought to address the influence of a sound versus affected first and/or second deciduous molar on the incidence of visible caries experience in the adjacent permanent first molar. Clinical and questionnaire data were obtained from a 6-year prospective oral health screening project in Flanders, Belgium (Signal-Tandmobiel project), where 4,468 children (born in 1989) were examined annually during their primary school time. A multiple survival model allowing for dependent data with possible censoring was applied. The impact of timing of tooth emergence (determining the period at risk), gender, presence of sealants and reported oral hygiene habits was also considered. Cavity formation in permanent first molars was clearly influenced by the status of the adjacent primary molars;the effect of the second deciduous molar was most pronounced. Moreover, if both deciduous molars experienced caries and the child presented with poor oral hygiene, a peak in cavity formation of the permanent first molar 1-2 years after emergence was noticed. On the other hand, if a child presented with good oral hygiene, no peak was observed; caries risk increased slightly over time. No significant benefit from restoring primary molars could be demonstrated, possibly because of methodological limitations.

Child↗