Declerck, D.

Hierarchical modeling of agreement (Article)

2012-12-10T00:00:00Z

Kappa-like agreement indexes are often used to assess the agreement among examiners on a categorical scale. They have the particularity of correcting the level of agreement for the effect of chance. In the present paper, we first define two agreement indexes belonging to this family in a hierarchical context. In particular, we consider the cases of a random and fixed set of examiners. Then, we develop a method to evaluate the influence of factors on these indexes. Agreement indexes are directly related to a set of covariates through a hierarchical model. We obtain the posterior distribution of the model parameters in a Bayesian framework. We apply the proposed approach on dental data and compare it with the generalized estimating equations approach.

Estimating emergence sequences of permanent teeth in Flemish schoolchildren using interval-censored biplots: A graphical display of tooth emergence sequences (Article)

2012-02-01T00:00:00Z

Objectives: The aim of the present study was to investigate the pattern of emergence of permanent teeth using nonparametric techniques. Materials and methods: Data were obtained from the Signal-Tandmobiel®project, a 6-year prospective dental study conducted in Flanders (Belgium) in which 4468 primary school children born in 1989 were annually examined. A new exploratory method for interval-censored data, the IC-biplot, was applied to estimate individual sequences of emergence. In addition, the method renders a nice graphical representation of both children and teeth in the plane where the individual sequences of emergence can easily be visualized. On the basis of the estimated individual sequences, their corresponding prevalences were calculated. Results: The study revealed that between 7 and 13 different sequences of emergence can be expected depending on gender and quadrant. The prevalences of the most frequent sequences in girls varied from 35% to 85% depending on the quadrant, while in boys they varied from 28% to 32%. Most sequences in the maxilla start with 6-1-2 and in the mandible with 1-6-2. Conclusions: The IC-biplot is a flexible procedure that allows an easy visualization of the pattern of emergence of permanent teeth. Rank orders derived from the IC-biplot confirm rank orders suggested earlier in the literature.

Examiner performance in calibration exercises compared with field conditions when scoring caries experience (Article)

2011-02-25T00:00:00Z

The objective of this study was to verify how valid misclassification measurements obtained from a 'pre-survey' calibration exercise are by comparing them to validation scores obtained in 'field' conditions. Validation data were collected from the 'Smile for Life' project, an oral health intervention study in Flemish children. A calibration exercise was organized under 'pre-survey' conditions (32 age-matched children examined by eight examiners and the benchmark scorer). In addition, using a pre-determined sampling scheme blinded to the examiners, the benchmark scorer re-examined between six and 11 children screened by each of the dentists during the survey. Factors influencing sensitivity and specificity for scoring caries experience (CE) were investigated, including examiner, tooth type, surface type, tooth position (upper/lower jaw, right/left side) and validation setting (pre-survey versus field). In order to account for the clustering effect in the data, a generalized estimating equations approach was applied. Sensitivity scores were influenced not only by the calibration setting (lower sensitivity in field conditions, p < 0.01), but also by examiner, tooth type (lower sensitivity in molar teeth, p < 0.01) and tooth position (lower sensitivity in the lower jaw, p < 0.01). Factors influencing specificity were examiner, tooth type (lower specificity in molar teeth, p < 0.01) and surface type (the occlusal surface with a lower specificity than other surfaces) but not the validation setting. Misclassification measurements for scoring CE are influenced by several factors. In this study, the validation setting influenced sensitivity, with lower scores obtained when measuring data validity in 'field' conditions. Results obtained in a pre-survey calibration setting need to be interpreted with caution and do not (always) reflect the actual performance of examiners during the field work.

Correcting for misclassification for a monotone disease process with an application in dental research (Article)

2010-12-30T00:00:00Z

Motivated by a longitudinal oral health study, we evaluate the performance of binary Markov models in which the response variable is subject to an unconstrained misclassification process and follows a monotone or progressive behavior. Theoretical and empirical arguments show that the simple version of the model can be used to estimate the prevalence, incidences, and misclassification parameters without the need of external information and that the incidence estimators associated with the model outperformed approaches previously proposed in the literature. We propose an extension of the simple version of the binary Markov model to describe the relationship between the covariates and the prevalence and incidence allowing for different classifiers. We implemented a Bayesian version of the extended model and show that, under the settings of our motivating example, the parameters can be estimated without any external information. Finally, the analyses of the motivating problem are presented. Copyright

Factors that influence data quality in caries experience detection: A multilevel modeling approach (Article)

2010-11-01T00:00:00Z

Caries experience detection is prone to misclassification. For this reason, calibration exercises which aim at assessing and improving the scoring behavior of dental raters are organized. During a calibration exercise, a sample of children is examined by the benchmark scorer and the dental examiners. This produces a 2 × 2 contingency table with the true and possibly misclassified responses. The entries in this misclassification table allow to estimate the sensitivity and the specificity of the raters. However, in many dental studies, the uncertainty with which sensitivity and specificity are estimated is not expressed. Further, caries experience data have a hierarchical structure since the data are recorded for the surfaces nested in the teeth within the mouth. Therefore, it is important to report the uncertainty using confidence intervals and to take the clustering into account. Here we apply a Bayesian logistic multilevel model for estimating the sensitivity and specificity. The main goal of this research is to find the factors that influence the true scoring of caries experience accounting for the hierarchical structure in the data. In our analysis, we show that the dentition type and tooth or surface type affect the quality of caries experience detection. Copyright

Measurement, analysis and interpretation of examiner reliability in caries experience surveys: some methodological thoughts (Article)

2010-10-13T00:00:00Z

Data obtained from calibration exercises are used to assess the level of agreement between examiners (and the benchmark examiner) and/or between repeated examinations by the same examiner in epidemiological surveys or large-scale clinical studies. Agreement can be measured using different techniques: kappa statistic, percentage agreement, dice coefficient, sensitivity and specificity. Each of these methods shows specific characteristics and has its own shortcomings. The aim of this contribution is to critically review techniques for the measurement and analysis of examiner agreement and to illustrate this using data from a recent survey in young children, the Smile for Life project. The above-mentioned agreement measures are influenced (in differing ways and extents) by the unit of analysis (subject, tooth, surface level) and the disease level in the validation sample. These effects are more pronounced for percentage agreement and kappa than for sensitivity and specificity. It is, therefore, important to include information on unit of analysis and disease level (in validation sample) when reporting agreement measures. Also, confidence intervals need to be included since they indicate the reliability of the estimate. When dependency among observations is present [as is the case in caries experience data sets with typical hierarchical structure (surface-tooth-subject)], this will influence the width of the confidence interval and should therefore not be ignored. In this situation, the use of multilevel modelling is necessary. This review clearly shows that there is a need for the development of guidelines for the measurement, interpretation and reporting of examiner reliability in caries experience surveys.

Statistics in Medicine: Editorial (Article)

2009-12-10T00:00:00Z

Caries experience in primary molars and its impact on the variability in permanent tooth emergence sequences (Article)

2009-11-01T00:00:00Z

Objectives: A history of caries in the primary molars is associated with an advanced emergence of their permanent successors. Hence, caries in the primary molars may have an impact on the emergence order of the permanent teeth. The aim of the present study was to fully investigate the variability in permanent tooth emergence, taking into account the (caries) status of the primary molars. Methods: For this purpose data available from the Signal Tandmobiel®project were used. In this prospective longitudinal survey data were collected from a representative sample of 4468 children, examined yearly by trained dentist-examiners. Bayesian statistical analyses taking into account the interval-censored character of the data were performed. Results: 56% of all examined primary molars were sound; between 2.5 and 7.2% of the first and second primary molars were extracted due to caries. When both primary molars were sound, the most prevalent emergence order was '4-3-5-7' (first premolar-canine-second premolar-second molar) in the maxilla and '3-4-5-7' in the mandible. When both maxillary primary molars were affected by caries (i.e., decayed, filled or extracted due to caries), the sequence '4-5-3-7' was the most prevalent whereas sequences '3-4-5-7' and '4-3-5-7' were less prevalent. When both mandibular primary molars were affected by caries, the prevalence of sequences '4-3-5-7', '4-3-7-5' and '4-5-3-7' increased whereas the prevalence of sequences '3-4-5-7' and '3-4-7-5' decreased. Conclusions: A history of caries in the primary molars is associated with an altered emergence order of canines, premolars and second molars.

On the estimation of the misclassification table for finite count data with an application in caries research (Article)

2009-06-01T00:00:00Z

We look at the correction for misclassification of possibly corrupted finite count data in epidemiological studies. In general, the misclassification probabilities are estimated from a validation study and used to correct for the distortion. However, most often the validation study is quite small implying that the misclassification probabilities are impossible to calculate or estimate with high variability if based on the multinomial distribution. To increase efficiency, we propose an approach based on the fact that to determine a count the examiner needs to evaluate all items that make up that count, called the double binomial (DB) approach. We suggest various extensions of the DB approach which might mimic better the scoring behaviour of the examiner relative to a gold standard. We evaluate the performance of our approach(es) to estimate the misclassification probabilities in comparison to the multinomial approach in an analytical way and in a simulation study. Finally, the practical use of our methods is exemplified on an oral health survey examining caries experience in 7-year-old Flemish children involving 16 dental examiners.