Cohen’s Kappa Coefficient as a Measure to Assess Classification Improvement following the Addition of a New Marker to a Regression Model

The need to search for new measures describing the classification of a logistic regression model stems from the difficulty in searching for previously unknown factors that predict the occurrence of a disease. A classification quality assessment can be performed by testing the change in the area under the receiver operating characteristic curve (AUC). Another approach is to use the Net Reclassification Improvement (NRI), which is based on a comparison between the predicted risk, determined on the basis of the basic model, and the predicted risk that comes from the model enriched with an additional factor. In this paper, we draw attention to Cohen’s Kappa coefficient, which examines the actual agreement in the correction of a random agreement. We proposed to extend this coefficient so that it may be used to detect the quality of a logistic regression model reclassification. The results provided by Kappa‘s reclassification were compared with the results obtained using NRI. The random variables’ distribution attached to the model on the classification change, measured by NRI, Kappa, and AUC, was presented. A simulation study was conducted on the basis of a cohort containing 3971 Poles obtained during the implementation of a lower limb atherosclerosis prevention program

International waist circumference percentile cut-offs for central obesity in children and adolescents aged 6-18 years

Context: No universal waist circumference (WC) percentile cut-offs used have been proposed for screening central obesity in children and adolescents. Objective: To develop international WC percentile cut-offs for children and adolescents with normal weight based on data from eight countries in different regions and examine the relation with cardiovascular risk. Design and Setting: We used pooled data on WC in 113,453 children and adolescents (males, 50.2%) aged 4-20 years from eight countries in different regions (Bulgaria, China, Iran, Korea, Malaysia, Poland, Seychelles, and Switzerland). We calculated WC percentile cut-offs in samples including or excluding children with obesity, overweight or underweight. WC percentiles were generated using the general additive model for location scale and shape (GAMLSS). We also estimated the predictive power of the WC 90th percentile cut-offs to predict cardiovascular risk using receiver operator characteristics curve analysis based on data from three countries that had available data (China, Iran and Korea). We also examined which WC percentiles connected with WC cut-offs for central obesity in adults (at age of 18 years). Main Outcome Measure: WC measured based on recommendation by the World Health Organization. Results: We validated the performance of the age- and sex- specific 90th percentile WC cut-offs calculated in children and adolescents (6-18 years of age) with normal weight (excluding youth with obesity, overweight or underweight) by linking it with cardiovascular risk (AUC: 0.69 for boys; 0.63 for girls). In addition, WC percentile among normal weight children linked relatively well with established WC cut-offs for central obesity in adults (e.g., AUC in US adolescents: 0.71 for boys; 0.68 for girls). Conclusion: The international WC cut-offs developed in this study could be useful to screen central obesity in children and adolescents aged 6-18 years and allow direct comparison of WC distributions between populations and over time.</p

Performance of Eleven Simplified Methods for the Identification of Elevated Blood Pressure in Children and Adolescents.

The identification of elevated blood pressure (BP) in children and adolescents relies on complex percentile tables. The present study compares the performance of 11 simplified methods for assessing elevated or high BP in children and adolescents using individual-level data from 7 countries. Data on BP were available for a total of 58 899 children and adolescents aged 6 to 17 years from 7 national surveys in China, India, Iran, Korea, Poland, Tunisia, and the United States. Performance of the simplified methods for screening elevated or high BP was assessed with receiver operating characteristic curve (area under the curve), sensitivity, specificity, positive predictive value, and negative predictive value. When pooling individual data from the 7 countries, all 11 simplified methods performed well in screening high BP, with high area under the curve values (0.84-0.98), high sensitivity (0.69-1.00), high specificity (0.87-1.00), and high negative predictive values (≥0.98). However, positive predictive value was low for most simplified methods, but reached ≈0.90 for each of the 3 methods, including sex- and age-specific BP references (at the 95th percentile of height), the formula for BP references (at the 95th percentile of height), and the simplified method relying on a child's absolute height. These findings were found independently of sex, age, and geographical location. Similar results were found for simplified methods for screening elevated BP. In conclusion, all 11 simplified methods performed well for identifying high or elevated BP in children and adolescents, but 3 methods performed best and may be most useful for screening purposes

Establishing International Blood Pressure References Among Nonoverweight Children and Adolescents Aged 6 to 17 Years.

BACKGROUND: Several distributions of country-specific blood pressure (BP) percentiles by sex, age, and height for children and adolescents have been established worldwide. However, there are no globally unified BP references for defining elevated BP in children and adolescents, which limits international comparisons of the prevalence of pediatric elevated BP. We aimed to establish international BP references for children and adolescents by using 7 nationally representative data sets (China, India, Iran, Korea, Poland, Tunisia, and the United States). METHODS AND RESULTS: Data on BP for 52 636 nonoverweight children and adolescents aged 6 to 19 years were obtained from 7 large nationally representative cross-sectional surveys in China, India, Iran, Korea, Poland, Tunisia, and the United States. BP values were obtained with certified mercury sphygmomanometers in all 7 countries by using standard procedures for BP measurement. Smoothed BP percentiles (50th, 90th, 95th, and 99th) by age and height were estimated by using the Generalized Additive Model for Location Scale and Shape model. BP values were similar between males and females until the age of 13 years and were higher in males than females thereafter. In comparison with the BP levels of the 90th and 95th percentiles of the US Fourth Report at median height, systolic BP of the corresponding percentiles of these international references was lower, whereas diastolic BP was similar. CONCLUSIONS: These international BP references will be a useful tool for international comparison of the prevalence of elevated BP in children and adolescents and may help to identify hypertensive youths in diverse populations

International Waist Circumference Percentile Cutoffs for Central Obesity in Children and Adolescents Aged 6 to 18 Years.

No universal waist circumference (WC) percentile cutoffs used have been proposed for screening central obesity in children and adolescents. To develop international WC percentile cutoffs for children and adolescents with normal weight based on data from 8 countries in different global regions and to examine the relation with cardiovascular risk. We used pooled data on WC in 113,453 children and adolescents (males 50.2%) aged 4 to 20 years from 8 countries in different regions (Bulgaria, China, Iran, Korea, Malaysia, Poland, Seychelles, and Switzerland). We calculated WC percentile cutoffs in samples including or excluding children with obesity, overweight, or underweight. WC percentiles were generated using the general additive model for location, scale, and shape (GAMLSS). We also estimated the predictive power of the WC 90th percentile cutoffs to predict cardiovascular risk using receiver operator characteristics curve analysis based on data from 3 countries that had available data (China, Iran, and Korea). We also examined which WC percentiles linked with WC cutoffs for central obesity in adults (at age of 18 years). WC measured based on recommendation by the World Health Organization. We validated the performance of the age- and sex-specific 90th percentile WC cutoffs calculated in children and adolescents (6-18 years of age) with normal weight (excluding youth with obesity, overweight, or underweight) by linking the percentile with cardiovascular risk (area under the curve [AUC]: 0.69 for boys; 0.63 for girls). In addition, WC percentile among normal weight children linked relatively well with established WC cutoffs for central obesity in adults (eg, AUC in US adolescents: 0.71 for boys; 0.68 for girls). The international WC cutoffs developed in this study could be useful to screen central obesity in children and adolescents aged 6 to 18 years and allow direct comparison of WC distributions between populations and over time

Height-specific blood pressure cutoffs for screening elevated and high blood pressure in children and adolescents: an International Study.

Pediatric blood pressure (BP) reference tables are generally based on sex, age, and height and tend to be cumbersome to use in routine clinical practice. In this study, we aimed to develop a new, height-specific simple BP table according to the international child BP reference table based on sex, age and height and to evaluate its performance using international data. We validated the simple table in a derivation cohort that included 58,899 children and adolescents aged 6-17 years from surveys in 7 countries (China, India, Iran, Korea, Poland, Tunisia, and the United States) and in a validation cohort that included 70,072 participants from three other surveys (China, Poland and Seychelles). The BP cutoff values for the simple table were calculated for eight height categories for both the 90th ("elevated BP") and 95th ("high BP") percentiles of BP. The simple table had a high performance to predict high BP compared to the reference table, with high values (boys/girls) of area under the curve (0.94/0.91), sensitivity (88.5%/82.9%), specificity (99.3%/99.7%), positive predictive values (93.9%/97.3%), and negative predictive values (98.5%/97.8%) in the pooled data from 10 studies. The simple table performed similarly well for predicting elevated BP. A simple table based on height only predicts elevated BP and high BP in children and adolescents nearly as well as the international table based on sex, age, and height. This has important implications for simplifying the detection of pediatric high BP in clinical practice