- Email: [email protected]
The GAMLSS. An innovative approach for calculating reference values
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Abstracts/Appetite 89 (2015) 301–330
The GAMLSS. An innovative approach for calculating reference values I. PIGEOT, on behalf of the IDEFICS consortium, Timm Intemann. Leibniz Institute for Prevention Research and Epidemiology – BIPS, Achterstr. 30, 28359 Bremen, Germany. [email protected] Age-dependent reference curves are widely used in paediatric routine visits for assessing the health status of children. The generalised additive model for location, scale and shape (GAMLSS; Stasinopoulos & Rigby, 2007) is a useful tool to derive such curves by modelling the influence of various covariates on clinical health parameters. GAMLSS is an extension of the well-known LMS method as it allows to account for more than one covariate and to model not only the location, shape and skewness, but also the kurtosis using various distributions (Cole et al., 2009). The complexity of GAMLSS requires that different statistical tools, i.e. Bayesian Information Criterion (BIC), Q–Q plots and wormplots should be used to assess the goodness of fit of the appropriate models. We will introduce the statistical background of GAMLSS and illustrate its application by various examples. This talk provides the methodological foundation for the calculation of clinical reference values in children. References Cole, T. J., Stanojevic, S., Stocks, J., Coates, A. L., Hankinson, J. L., & Wade, A. M. (2009). Age- and size-related reference ranges. A case study of spirometry through childhood and adulthood. Statistics in Medicine, 28, 880–898. Stasinopoulos, D. M., & Rigby, R. A. (2007). Generalized additive models for location scale and shape (GAMLSS). Journal of Statistical Software, 23(7), 1–46. http://dx.doi.org/10.1016/j.appet.2014.12.077
Percentiles of markers of insulin resistance in pre-pubertal normal-weight European children from the IDEFICS cohort J. PEPLIES, on behalf of the IDEFICS consortium. Leibniz Institute for Prevention Research and Epidemiology – BIPS, Achterstraße 30, 28207 Bremen, Germany. [email protected] The aim of this study is to present age- and sex-specific reference values of insulin, glucose, glycosylated haemoglobin (HbA1c) and the homeostasis model assessment to quantify insulin resistance (HOMA-IR) for pre-pubertal children. The reference population consists of 7074 normal-weight 3- to 10.9-year-old pre-pubertal children from 8 European countries who participated in at least one wave of the IDEFICS (“Identification and prevention of dietary- and lifestyleinduced health effects in children and infants”) surveys (2007– 2010) for whom standardised laboratory measurements were obtained. Percentile curves of insulin, glucose, HbA1c and HOMAIR were calculated as a function of age stratified by sex using the
General Additive Model for Location Scale and Shape (GAMLSS) method. Levels of insulin, fasting glucose and HOMA-IR continuously show an increasing trend with age while HbA1c shows an upward trend only beyond the age of 8 years. Insulin and HOMAIR values are higher in girls of all age groups, whereas glucose values are slightly higher in boys. Our study provides the first standardised reference values for an international European children’s population and the up to now largest dataset of healthy prepubertal children to model reference percentiles for markers of insulin resistance. Our percentiles are in good accordance with previously measured values for markers of glucose metabolism, except for Hb1Ac, where only few data are available from population based studies. http://dx.doi.org/10.1016/j.appet.2014.12.078
Europe-specific percentile reference values for anthropometric body composition indices in children of the IDEFICS study P. NAGY, E. KOVACS, D. MOLNAR, on behalf of IDEFICS consortium. Department of Pediatrics, University of Pécs, Pécs, Hungary. [email protected] In order to characterise the nutritional status in children with obesity or wasting conditions, European anthropometric reference values for body composition measures beyond the body mass index (BMI) are needed. Differentiated assessment of body composition in children has long been hampered by the lack of appropriate references. The aim of our study is to provide percentiles for body composition indices in normal weight European children, based on the IDEFICS cohort (Identification and prevention of Dietary- and lifestyle-induced health Effects in Children and infantS). Overall 18,745 2.0- to 10.9-year-old children from 8 countries participated in the study. Children classified as overweight/obese or underweight according to IOTF were excluded from the analysis. 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th and 99th percentile curves of anthropometric measurements (N = 8129–12,830); stratified by sex were calculated and smoothed by using GAMLSS. Age- and sex-specific percentile values of the most important anthropometric measures related to the degree of adiposity (BMI, biceps triceps, subscapular and suprailiac skinfolds, sum of skinfolds, fat mass index, neck circumference, waist circumference and waist-to-height ratio) are presented. The newly introduced percentile curves may aid a differentiated assessment of total and abdominal adiposity in European children. The IDEFICS study was funded by the 6th Framework programme of the European Commission. The publication of papers on reference values is supported by the Volkswagen Foundation. http://dx.doi.org/10.1016/j.appet.2014.12.079
Abstracts/Appetite 89 (2015) 301–330
The GAMLSS. An innovative approach for calculating reference values I. PIGEOT, on behalf of the IDEFICS consortium, Timm Intemann. Leibniz Institute for Prevention Research and Epidemiology – BIPS, Achterstr. 30, 28359 Bremen, Germany. [email protected] Age-dependent reference curves are widely used in paediatric routine visits for assessing the health status of children. The generalised additive model for location, scale and shape (GAMLSS; Stasinopoulos & Rigby, 2007) is a useful tool to derive such curves by modelling the influence of various covariates on clinical health parameters. GAMLSS is an extension of the well-known LMS method as it allows to account for more than one covariate and to model not only the location, shape and skewness, but also the kurtosis using various distributions (Cole et al., 2009). The complexity of GAMLSS requires that different statistical tools, i.e. Bayesian Information Criterion (BIC), Q–Q plots and wormplots should be used to assess the goodness of fit of the appropriate models. We will introduce the statistical background of GAMLSS and illustrate its application by various examples. This talk provides the methodological foundation for the calculation of clinical reference values in children. References Cole, T. J., Stanojevic, S., Stocks, J., Coates, A. L., Hankinson, J. L., & Wade, A. M. (2009). Age- and size-related reference ranges. A case study of spirometry through childhood and adulthood. Statistics in Medicine, 28, 880–898. Stasinopoulos, D. M., & Rigby, R. A. (2007). Generalized additive models for location scale and shape (GAMLSS). Journal of Statistical Software, 23(7), 1–46. http://dx.doi.org/10.1016/j.appet.2014.12.077
Percentiles of markers of insulin resistance in pre-pubertal normal-weight European children from the IDEFICS cohort J. PEPLIES, on behalf of the IDEFICS consortium. Leibniz Institute for Prevention Research and Epidemiology – BIPS, Achterstraße 30, 28207 Bremen, Germany. [email protected] The aim of this study is to present age- and sex-specific reference values of insulin, glucose, glycosylated haemoglobin (HbA1c) and the homeostasis model assessment to quantify insulin resistance (HOMA-IR) for pre-pubertal children. The reference population consists of 7074 normal-weight 3- to 10.9-year-old pre-pubertal children from 8 European countries who participated in at least one wave of the IDEFICS (“Identification and prevention of dietary- and lifestyleinduced health effects in children and infants”) surveys (2007– 2010) for whom standardised laboratory measurements were obtained. Percentile curves of insulin, glucose, HbA1c and HOMAIR were calculated as a function of age stratified by sex using the
General Additive Model for Location Scale and Shape (GAMLSS) method. Levels of insulin, fasting glucose and HOMA-IR continuously show an increasing trend with age while HbA1c shows an upward trend only beyond the age of 8 years. Insulin and HOMAIR values are higher in girls of all age groups, whereas glucose values are slightly higher in boys. Our study provides the first standardised reference values for an international European children’s population and the up to now largest dataset of healthy prepubertal children to model reference percentiles for markers of insulin resistance. Our percentiles are in good accordance with previously measured values for markers of glucose metabolism, except for Hb1Ac, where only few data are available from population based studies. http://dx.doi.org/10.1016/j.appet.2014.12.078
Europe-specific percentile reference values for anthropometric body composition indices in children of the IDEFICS study P. NAGY, E. KOVACS, D. MOLNAR, on behalf of IDEFICS consortium. Department of Pediatrics, University of Pécs, Pécs, Hungary. [email protected] In order to characterise the nutritional status in children with obesity or wasting conditions, European anthropometric reference values for body composition measures beyond the body mass index (BMI) are needed. Differentiated assessment of body composition in children has long been hampered by the lack of appropriate references. The aim of our study is to provide percentiles for body composition indices in normal weight European children, based on the IDEFICS cohort (Identification and prevention of Dietary- and lifestyle-induced health Effects in Children and infantS). Overall 18,745 2.0- to 10.9-year-old children from 8 countries participated in the study. Children classified as overweight/obese or underweight according to IOTF were excluded from the analysis. 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th and 99th percentile curves of anthropometric measurements (N = 8129–12,830); stratified by sex were calculated and smoothed by using GAMLSS. Age- and sex-specific percentile values of the most important anthropometric measures related to the degree of adiposity (BMI, biceps triceps, subscapular and suprailiac skinfolds, sum of skinfolds, fat mass index, neck circumference, waist circumference and waist-to-height ratio) are presented. The newly introduced percentile curves may aid a differentiated assessment of total and abdominal adiposity in European children. The IDEFICS study was funded by the 6th Framework programme of the European Commission. The publication of papers on reference values is supported by the Volkswagen Foundation. http://dx.doi.org/10.1016/j.appet.2014.12.079