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Josep L Carrasco

Publications and source records attributed to Josep L Carrasco.

5 recordsLinked to original sources

A repeated measures concordance correlation coefficient.

The concordance correlation coefficient is commonly used to assess agreement between two raters or two methods of measuring a response when the data are measured on a continuous scale. However, the situation may arise in which repeated measurements are taken for each rater or method, e.g. longitudinal studies in clinical trials or bioassay data with subsamples. This paper proposes a coefficient for measuring agreement between two raters or two methods of measuring a response in the presence of repeated measurements. We illustrate the methodology with examples comparing (1) 1-hr versus 2-hr blood draws for measuring cortisol in an asthma clinical trial and (2) two measurements of percentage body fat, from skinfold calipers and dual energy X-ray absorptiometry.

Absorptiometry, Photon↗

The use of indexes evaluating the adherence to the Mediterranean diet in epidemiological studies: a review.

The purpose of this paper is to review some of the methods that several epidemiological studies use to evaluate the adherence of a population to the Mediterranean diet pattern. Among these methods, diet indexes attempt to make a global evaluation of the quality of the diet based on a traditional Mediterranean reference pattern, described as a priori, general and qualitative. The Mediterranean diet indexes, hence, summarise the diet by means of a single score that results from a function of different components, such as food, food groups or a combination of foods and nutrients. The reviewed evaluation methods can be classified into three categories depending on the way they are calculated: (1) those based on a positive or negative scoring of the components, (2) those that add or substract standardised components, and (3) those that are based on a ratio between components. Dietary scores have been used to explore the multiple associations between the Mediterranean diet, as an integral entity, and health parameters such as life expectancy or the incidence of obesity, cardiovascular diseases and some types of cancers. Moreover, these indexes are also useful tools to measure food consumption trends and to identify the involved factors, as well as to develop comprehensive public health nutrition recommendations. A more precise and quantitative definition of the Mediterranean diet is required if the adherence to such a dietary pattern is intended to be more accurately measured. Other aspects of the Mediterranean diet indexes should also be taken into account, like the inclusion of typical Mediterranean foods such as nuts and fish and the validation of the dietary pattern approach by using biomarkers.

Biomarkers↗

Concordance correlation coefficient applied to discrete data.

In any field in which decisions are subject to measurements, interchangeability between the methods used to obtain these measurements is essential. To consider methods as interchangeable, a certain degree of agreement is needed between the measurements they provide. The concordance correlation coefficient is an index that assesses the strength of agreement and it has been widely applied in situations in which measurements are made on a continuous scale. Recently the concordance correlation coefficient has been defined as a specific intraclass correlation coefficient estimated by the variance components of a Normal-Normal mixed linear model. Although this coefficient was defined for the continuous scale case, it may also be used with a discrete scale. In this case the data are often transformed and normalized, and the concordance correlation is applied. This study discusses the expression of the concordance correlation coefficient for discrete Poisson data by means of the Poisson-Normal generalized linear mixed model. The behaviour of the concordance correlation coefficient estimate is assessed by means of a simulation study, in which the estimates were compared using four models: three Normal-Normal mixed models with raw data, log-transformed data and square-root transformed data, and the Poisson-Normal generalized linear mixed model. An example is provided in which two different methods are used to measure CD34+ cells.

Biomedical Research↗

The structural error-in-equation model to evaluate individual bioequivalence.

Individual bioequivalence is assessed using an extension of the classical structural equation model, known as the error-in-equation model. This procedure estimates the relationship between individual means, as well as the variance-covariance parameters, of the bioavailabilities measurement model, by considering individual means related through a straight line with a random term, whereas the classical structural equation considers a deterministic linear relationship. We discuss the implications of this approach in terms of the bioavailabilities measurement model and how to test the overall hypothesis of individual bioequivalence. Both models are compared in a simulation study and a case example is presented.

Analysis of Variance↗

Estimating the generalized concordance correlation coefficient through variance components.

The intraclass correlation coefficient (ICC) and the concordance correlation coefficient (CCC) are two of the most popular measures of agreement for variables measured on a continuous scale. Here, we demonstrate that ICC and CCC are the same measure of agreement estimated in two ways: by the variance components procedure and by the moment method. We propose estimating the CCC using variance components of a mixed effects model, instead of the common method of moments. With the variance components approach, the CCC can easily be extended to more than two observers, and adjusted using confounding covariates, by incorporating them in the mixed model. A simulation study is carried out to compare the variance components approach with the moment method. The importance of adjusting by confounding covariates is illustrated with a case example.

Analysis of Variance↗