Statistical inference for the area under the receiver operating characteristic curve in the presence of random measurement error

Maximum Phonation Times as Biomarkers of Lung Function

PURPOSE

To verify whether measurements of maximal phonation times are biomarkers of forced vital capacity in patients with chronic obstructive pulmonary disease, and to characterize the vocal aspects of these patients, taking into account variables, such as age, body mass index, use of bronchodilators, presence of symptoms, and quality of life related to voice.

METHODS

Complete records of 25 subjects with chronic obstructive pulmonary disease, both sexes, aged 31 to 85 years, evaluated by forced vital capacity, maximum phonation times of /a/, and numerical count and number reached at this count, Vocal Symptom Scale, Voice Quality of Life. Data were presented descriptively and statistically analyzed using Student's t test for independent samples and Mann-Whitney U test. A significance level of 5% was accepted. The receiver operating characteristic curve was plotted and the standardized value of forced vital capacity <80% was considered as an indicator of pulmonary dysfunction.

RESULTS

Patients exhibited reduced maximum phonation times for /a/, numeric counting, and reached digits in counting; discrepancies in Vocal Signs and Symptoms and Voice Quality of Life Scale scores. Numeric counting times of up to 12.5 seconds indicated that forced vital capacity may be impaired.

CONCLUSION

The patients with chronic obstructive pulmonary disease examined in this study exhibited vocal deviations as evidenced by reduced maximum phonation times of /a/, numeric counting, and the digit reached during counting, as well as deviations in vocal self-assessment. Maximum phonation time in numerical counting was considered a biomarker of pulmonary function impairment.

Identification of potential serum biomarkers for congenital heart disease children with pulmonary arterial hypertension by metabonomics

BACKGROUND

Pulmonary arterial hypertension is a common complication in patients with congenital heart disease. In the absence of early diagnosis and treatment, pediatric patients with PAH has a poor survival rate. Here, we explore serum biomarkers for distinguishing children with pulmonary arterial hypertension associated with congenital heart disease (PAH-CHD) from CHD.

METHODS

Samples were analyzed by nuclear magnetic resonance spectroscopy-based metabolomics and 22 metabolites were further quantified by ultra-high-performance liquid chromatography-tandem mass spectroscopy.

RESULTS

Serum levels of betaine, choline, S-Adenosyl methionine (SAM), acetylcholine, xanthosine, guanosine, inosine and guanine were significantly altered between CHD and PAH-CHD. Logistic regression analysis showed that combination of serum SAM, guanine and N-terminal pro-brain natriuretic peptide (NT-proBNP), yielded the predictive accuracy of 157 cases was 92.70% with area under the curve of the receiver operating characteristic curve value of 0.9455.

CONCLUSION

We demonstrated that a panel of serum SAM, guanine and NT-proBNP is potential serum biomarkers for screening PAH-CHD from CHD.

Physical activity and daily steps cut offs points for overweight/obesity prevention among eight Latin American countries

This study aims to establish cut-off points for the number of minutes of physical activity intensity and the number of daily steps that identify overweight/obesity in adolescents, adults, and older adults. This study examined data from 2737 participants. Physical activity intensity and the number of daily steps were assessed using GT3X+ ActiGraph model accelerometers. Body mass index, waist-to-height ratio, and waist-to-hip ratio were used as indicators of overweight/obesity. The cut-off points for moderate-to-vigorous physical activity for the prevention of overweight/obesity according to body mass index in women ranged from 15.1 to 30.2 min/day; in men, the values were from 15.4 to 33.8 min/day. The lowest cut-off point for daily steps was established in the adolescent group for women and men (7304 and 5162). The highest value in women was 11,412 (51-65 years) and 13,234 in men (18-30 years). Results from measurements different from BMI, show average cut-off points for moderate-to-vigorous physical activity and daily steps of 29.1/8348 and 43.5/10,456 according to waist-to-height ratio; and results of 29.3/11,900 and 44.3/11,056 according to the waist-to-hip ratio; in women and men respectively. A more specific recommendation of physical activity and daily steps adjusted by sex and age range is suggested to prevent overweight/obesity.

Anthropometric indicators of body fat as discriminators of low levels of cardiorespiratory fitness in adolescents

PURPOSE

To evaluate the discriminatory power of anthropometric indicators of body fat (BF) for identifying low levels of cardiorespiratory fitness, as well as the association between cutoff points and low levels of cardiorespiratory fitness in adolescents.

DESIGN AND METHODS

This is a cross-sectional study involving 1132 students (age 14-19 years). The following anthropometric variables were measured according to international standards: body mass index (BMI), waist circumference (WC), waist-to-height ratio (WHtR), triceps skinfold thickness (TR), subscapular skinfold (SS), suprailiac skinfold (SI), sum of triceps and subscapular skinfolds (∑TR + SS), and sum of triceps, subscapular and suprailiac skinfolds (∑TR + SS + SI). The BF percentage was calculated using the equations of Lohman (1986) (%FL), Slaughter et al. (1988) (%FS), and Boileau et al. (1985) (%FB).

RESULTS

Except for TR, WC, WHtR and BMI, boys with values for the other anthropometric indicators (SS, SI, ∑TR + SS, ∑TR + SS + SI, %FL, %FS, %FB) above the cutoff point were more likely to have low levels of cardiorespiratory fitness. Girls with values for TR, ∑TR + SS, %FB and %FL above the cutoff points were more likely to have low levels of cardiorespiratory fitness.

CONCLUSIONS

Anthropometric indicators had discriminatory power to identify low levels of cardiorespiratory fitness.

PRACTICE IMPLICATIONS

The reported anthropometric indicators, indexes and equations can be used by healthcare professionals in clinical practice and by school teachers as a simple, fast and inexpensive alternative to identify low levels of cardiorespiratory fitness.

A Wilcoxon-Mann-Whitney Test for Latent Variables

We propose an extension of the Wilcoxon–Mann–Whitney test to compare two groups when the outcome variable is latent. We empirically demonstrate that the test can have superior power properties relative to tests based on Structural Equation Modeling for a variety of settings. In addition, several other advantages of the Wilcoxon–Mann–Whitney test are retained such as robustness to outliers and good small sample performance. We demonstrate the proposed methodology on a case study.

Development and Validation of Diagnostic Models for Hand-Foot-and-Mouth Disease in Children

Objective

To find risk markers and develop new clinical predictive models for the differential diagnosis of hand-foot-and-mouth disease (HFMD) with varying degrees of disease.

Methods

19766 children with HFMD and 64 clinical indexes were included in this study. The patients included in this study were divided into the mild patients' group (mild) with 12292 cases, severe patients' group (severe) with 6508 cases, and severe patients with respiratory failure group (severe-RF) with 966 cases. Single-factor analysis was carried out on 64 indexes collected from patients when they were admitted to the hospital, and the indexes with statistical differences were selected as the prediction factors. Binary multivariate logistic regression analysis was used to construct the prediction models and calculate the adjusted odds ratio (OR).

Results

SP, DP, NEUT#, NEUT%, RDW-SD, RDW-CV, GGT, CK/CK-MB, and Glu were risk markers in mild/severe, mild/severe-RF, and severe/severe-RF. Glu was a diagnostic marker for mild/severe-RF (AUROC = 0.80, 95% CI: 0.78-0.82); the predictive model constructed by temperature, SP, MOMO%, EO%, RDW-SD, GLB, CRP, Glu, BUN, and Cl could be used for the differential diagnosis of mild/severe (AUROC > 0.84); the predictive model constructed by SP, age, NEUT#, PCT, TBIL, GGT, Mb, β2MG, Glu, and Ca could be used for the differential diagnosis of severe/severe-RF (AUROC > 0.76).

Conclusion

By analyzing clinical indicators, we have found the risk markers of HFMD and established suitable predictive models.

Physical activity and sedentary behavior as multimorbidity discriminators among elderly Brazilians: a cross-sectional study

BACKGROUND

Associations between behaviors and individual chronic diseases have been demonstrated. However, the relationship between time spent on sedentary behavior and multimorbidity remains less clear.

OBJECTIVE

To identify the predictive power of various intensities of physical activity versus sedentary behavior, as discriminatory factors for cardiometabolic multimorbidity (cardiovascular diseases and diabetes) in the elderly.

DESIGN AND SETTING

Cross-sectional study in different residential census tracts and residential households in Florianópolis (SC).

METHODS

The participants were 425 elderly people (65% women) from the EpiFloripa Aging study in 2014. Sociodemographic variables and self-reported incidence of cardiovascular diseases and diabetes were obtained via a questionnaire. Light physical activity (LPA), moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) were measured using accelerometers. The analyses were stratified according to sex and included a diagnosis for interpretation. Behaviors were taken into consideration if their predictive power in terms of area under the receiver operating characteristic (ROC) curve was greater than 0.50. The time cutoff point was defined from sensitivity and specificity.

RESULTS

For older adult men with diabetes, the predictive value of MVPA for absence of multi-morbidity was an area of 0.75 (95% confidence interval, CI: 0.538-0.962), and a cutoff of 17 minutes per day. Older adult women with diabetes had an area of 0.71 (95% CI: 0.524-0.866) and a cutoff of 10 minutes per day. LPA and SB did not present predictive values.

CONCLUSION

The time spent on MVPA is a predictor of absence of multimorbidity in elderly people with diabetes, for both sexes.

Prevalence and factors associated with chronic back problem in women of childbearing age

Chronic Back Problem (CBP) is a public health concern. In Brazil, data from the National Health Survey (PNS) estimated 27.0 million people (18.5%) who reported CBP, affecting more women than men. This study aims to identify the factors associated with CBP among women of childbearing age. It is a cross-sectional study carried out with data from the PNS, where the dependent variable was the prevalence of CBP, and associated factors included socio-demographic items, life habits, reproductive history, nutritional status, diagnosis of depression and health perception. A total of 22,621 women aged 18 to 49 years were interviewed. Of these, 14.8% reported having CBP. The risk factors studied were: increased age; living with spouse; multiparity; smoking; overweight or obese, having Waist Circumference (WC) above 80cm and Circumference/Height (C/E) index above 0.5; negative self-perception of health; and depression. The only protective factor associated with CBP risk reduction was education level. We conclude that age, living with a spouse/partner, smoking, multiparity, being overweight or obese, increased risk for cardiovascular diseases, depression and negative self-perceived health are associated with the development of CBP in women of childbearing age.

Discriminatory power of Stroke Specific Quality of Life questionnaire items to evaluate the participation component of the International Classification of Functioning, Disability and Health

Background/aims

This study aimed to estimate the discriminatory power of 26 items on the Stroke Specific Quality of Life Scale questionnaire to evaluate the participation component of the International Classification of Functioning, Disability and Health.

Methods

A prospective study was conducted using accuracy procedures based on the Standards for Reporting Diagnostic Accuracy Studies to evaluate individuals with hemiparesis stemming from a stroke. Discriminatory power was estimated based on the area under the receiver operating characteristic curve with a 95% confidence interval. Two groups were defined for the analysis: community-dwelling and institutionalised individuals. A 5% level of significance (α=0.05) was considered for all analyses.

Results

The area under the receiver operating characteristic curve was 0.888 (95% confidence interval: 0.794–0.949; P=0.001). Analysis indicated a cut-off point of ≥80 with 73.9% sensitivity and 100% specificity.

Conclusions

The 26 items of the Stroke Specific Quality of Life questionnaire that evaluate the participation component of the International Classification of Functioning, Disability and Health demonstrate adequate discriminatory power. A cut-off point of ≥80 seems to best discriminate the perception of participation between community-dwelling and institutionalised stroke survivors.

Validity Evidence of an Instrument for Mindfulness Assessment (MA) Based on its Internal Structure and External Criterion

Abstract Operationalizing the concept of mindfulness has been a challenge for researches. In this article, we present and discuss the procedures for the assessment of the internal structure and validity of the criteria for Mindfulness Assessment (MAP), as well as the results obtained. The collection of factors was done by exploratory factor analysis (EFA), and item- selection by item response theory (IRT). This study counted with 788 Brazilians, with ages ranging from 17 to 65 years (M = 26.11; SD = 9.59); 79% of which were women. Four factors were extracted: Mindfulness (α = 0.88), Attention (α = 0.84), Acceptance (α = 0.74) and Novelty seeking (α = 0.62). 47 items were retained in the MAP. We also compared the scores between non-meditator (n = 653) and meditator (n = 112) respondents. Analyses by IRT showed the items to be adequately adjusted. Significant differences between scores of meditators and non-meditator respondents were revealed. These findings suggest that the MAP is a valid and reliable instrument, regarding its internal structure and criterion-related evidence, which suggests its appropriateness in the study of adults.

Pulmonary function and functional capacity cut-off point to establish sarcopenia and dynapenia in patients with COPD

Objective

To establish a cut-off point for clinical and functional variables to determinate sarcopenia and dynapenia in COPD patients, and to analyze the impact of skeletal muscle dysfunction (SMD) on these variables.

Methods

Cross-sectional study, screened COPD patients for sarcopenia or dynapenia through low muscle mass and hand grip strength (HGS). Clinical variables: pulmonary function, respiratory muscle strength and functional capacity (FC). The precision of the variables in determining points of predictive cut-off for sarcopenia or dynapenia were performed using the Receiver Operating Characteristic curve and two-way analysis of variance.

Results

20 COPD patients stratified for sarcopenia (n = 11) and dynapenia (n = 07). Sarcopenia group presented lower lean mass and lower maximal inspiratory pressure (MIP), decreased HGS, reduced FC (p<0.050). Dynapenia group presented reduced MIP, lower HGS and walked a shorter distance at Incremental shuttle walk test (ISWT) (p<0.050). We found cut-off points of forced expiratory volume in one second (FEV1), MIP and maximal expiratory pressure (MEP) and ISWT. It is possible to identify sarcopenia or dynapenia in these patients. We found the coexistence of the conditions (SMD effect) in COPD – reduction in the distance in the ISWT (p = 0.002) and %ISWT (p = 0.017).

Conclusion

In moderate to very severe COPD patients the sarcopenia could be predicted by FEV₁ (%predicted) < 52, MIP < 73 cmH2O, MEP < 126 cmH2O and distance traveled of < 295 m in ISWT. Whereas dynapenia could be predicted by FEV₁ < 40%, MIP < 71 cmH2O, MEP < 110 cmH2O and distance of < 230 m traveled in ISWT.

Diagnosis of acute pediatric appendicitis from children with inflammatory diseases by combination of metabolic markers and inflammatory response variables

BACKGROUND

The discovery of new metabolic markers may be helpful for early diagnosis of acute pediatric appendicitis (APA). However, no studies have been reported regarding identification of potential metabolic markers for the APA diagnosis by metabonomics.

METHODS

Serum samples of APA (n=32), non-appendicitis inflammation (NAI, n=32) and healthy children (HS, n=65) were analyzed by the 1H NMR-based metabonomics. A logistic regression model was established to screen the most efficient markers combinations for classification. Forty double-blind samples were further validated the model.

RESULTS

Nine blood metabolites that were different in the APA group from other groups were identified. To differentiate APA from HS, single variable of acetate, formate, white blood cell (WBC) and C-reactive protein (CRP) showed a high diagnostic value (area under the receiver operating characteristic [AUROC]<0.92), while they had a weak diagnostic value (AUROC<0.77) for identifying the APA and NAI. By contrast, the AUROC values of leucine (0.799) were higher than that of WBC and CRP. A combination of five variables, i.e. leucine, lactate, betaine, WBC and CRP, showed a high diagnostic value (AUROC=0.973) for the APA discriminating from the NAI, and the sensitivity and specificity were 93.8% and 93.7%, respectively. Further double-blind sample prediction showed that the accuracy of the model was 85% for 40 unknown samples.

CONCLUSIONS

The current study provides useful information in our understanding of the metabolic alterations associated with APA and indicates that measurement of these metabolites in serum effectively aids in the clinical identification of APA.

Calf circumference: clinical validation for evaluation of muscle mass in the elderly

OBJECTIVE

To validate calf circumference as a technology for assessing muscle mass in the elderly.

METHOD

Cross-sectional study with 132 elderly people from Goiânia, Goiás, Brazil. Decreased muscle mass was determined by the skeletal muscle mass index (IME) using Dual Energy X-Ray Absortometry (DEXA). The cutoff circumferences (CC) cutoff points to indicate muscle mass decrease were estimated by ROC curve, sensitivity, specificity and accuracy.

RESULTS

The most accurate cut-off points for detecting decreased muscle mass in the elderly were 34 cm for men (sensitivity: 71.5%, specificity: 77.4%) and 33 cm for women (sensitivity: 80.0%; specificity: 84.6%).

CONCLUSION

CC can be used as a measure for early identification of muscle mass decrease in routine evaluations of the elderly in primary care.

Discovery and Validation of Potential Serum Biomarkers for Pediatric Patients with Congenital Heart Diseases by Metabolomics

To identify and screen serum biomarkers to determine pediatric patients with congenital heart diseases (PCH) from healthy control children (NC), a total of 614 clinically diagnosed subjects from three hospitals, including 491 PCH and 234 NC, were enrolled for nontargeted proton nuclear magnetic resonance spectroscopy (¹H NMR)-based and targeted ultra-high-performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS)-based metabolomics studies. Nineteen serum metabolites distinguishing PCH from NC were identified by ¹H NMR-based metabolomic analysis. The amino acid and choline metabolic pathways were considered to be closely related to PCH. The serum levels of 13 metabolites in these two pathways were further determined by UPLC-MS/MS and observed to be altered significantly in PCH. Taurine, glutamine, and glutamate presented considerable diagnostic value for the diagnosis of PCH (AUROC > 0.80). Logistic regression analysis showed that a combination of four variables, namely, betaine, taurine, glutamine, and phenylalanine, yields a high diagnostic value (AUROC = 0.949) and prediction accuracy (89.1%) for differentiating PCH from the NC, and the sensitivity and specificity were 93.9 and 95.2%, respectively. Further double-blind sample prediction showed that the accuracy of the model was 83.8% for 80 unknown samples. Our results showed that the serum amino acid and choline metabolite levels in PCH were changed considerably. The combination of four metabolites, namely, betaine, taurine, glutamine, and phenylalanine, can be used as potential serum biomarkers in PCH diagnosis, which contributes to the early PCH screening.

Waist circumference percentile curves as a screening tool to predict cardiovascular risk factors and metabolic syndrome risk in Brazilian children

The goals of this study were to develop reference values for waist circumference (WC) in Brazilian children between 6-10 years old and to evaluate the WC performance in predicting cardiovascular risk factors and metabolic syndrome (MetS) in children. This is a population-based epidemiological cross-sectional study, in which 1,397 children participated, with a 6-10 years old probability sampling and from public and private schools in the city of Uberaba, Minas Gerais State, Brazil. WC was measured at the waist narrowest point (WC1) and at the umbilicus level (WC2). Blood samples and blood pressure were collected to determine the MetS diagnosis. There was a significant effect of age (p = 0.001), anatomical point (WC1 vs. WC2, p = 0.001) and sex-anatomical point interaction (p = 0.016) for WC. Smoothed sex- and age-specific 5th, 10th, 25th, 50th, 75th, 90th and 95th percentile curves of WC1 and WC2 were designed by the LMS method. WC was accurate to predict MetS, for all ages [area under the ROC curve (AUC) > 0.79 and p < 0.05], regardless of sex. This study presented percentile curves for WC at two anatomical points in a representative sample of Brazilian children. Furthermore, WC was shown to be a strong predictor of cardiovascular risk factors and MetS in children.

Skinfold reference curves and their use in predicting metabolic syndrome risk in children

OBJECTIVES

To draw skinfold (SF) reference curves (subscapular, suprailiac, biceps, triceps) and to determine SF cutoff points for predicting the risk of metabolic syndrome (MetS) in children aged 6-10 years old.

METHODS

This was a cross-sectional study with a random sample of 1480 children aged 6-10 years old, 52.2% females, from public and private schools located in the urban and rural areas of the municipality of Uberaba (MG). Anthropometry, blood pressure, and fasting blood samples were taken at school, following specific protocols. The LMS method was used to draw the reference curves and ROC curve analysis to determine the accuracy and cutoff points for the evaluated skinfolds.

RESULTS

The four SF evaluated (subscapular, suprailiac, biceps, and triceps) and their sum (∑4SF) were accurate in predicting MetS for both girls and boys. Additionally, cutoffs have been proposed and percentile curves (p5, p10, p25, p50, p75, p90, and p95) were outlined for the four SF and ∑4SF, for both genders.

CONCLUSION

SF measurements were accurate in predicting metabolic syndrome in children aged 6-10 years old. Age- and gender-specific smoothed percentiles curves of SF provide a reference for the detection of risk for MetS in children.

Association between Blood Pressure and Birth Weight among Rural South African Children: Ellisras Longitudinal Study

The aim of this cross-sectional study was to investigate the association between birth weight, underweight, and blood pressure (BP) among Ellisras rural children aged between 5 and 15 years. Data were collected from 528 respondents who participated in the Ellisras Longitudinal Study (ELS) and had their birth weight recorded on their health clinic card. Standard procedure was used to measure the anthropometric measurements and BP. Linear regression was used to assess BP, underweight variables, and birth weight. Logistic regression was used to assess the association of hypertension risks, low birth weight, and underweight. The association between birth weight and BP was not statistically significant. There was a significant (p < 0.05) association between mean BP and the sum of four skinfolds (β = 0.26, 95% CI 0.15-0.23) even after adjusting for age (β = 0.18, 95% CI 0.01-0.22). Hypertension was significantly associated with weight for age z-scores (OR = 5.13, 95% CI 1.89-13.92) even after adjusting for age and sex (OR = 5.26, 95% CI 1.93-14.34). BP was significantly associated with the sum of four skinfolds, but not birth weight. Hypertension was significantly associated with underweight. Longitudinal studies should confirm whether the changes in body weight we found can influence the risk of cardiovascular diseases.

Time Spent Sitting Is Associated with Changes in Biomarkers of Frailty in Hospitalized Older Adults: A Cross Sectional Study

Background: Sedentary behavior has gained prominence in the literature as a risk factor for health and mortality independent of physical activity level; however, little is known about the relationship of sedentary behavior with frailty in older adults. The aim of this study was to investigate if time spent sitting can be used as a discriminator of frailty in older hospitalized persons.

Methods: The study included 162 hospitalized inpatients aged ≥60 years. Blood samples were taken for analyzing leukocyte counts and serum concentrations of C-reactive protein (CRP). Participants also answered a questionnaire about time spent sitting. Frailty was determined from a combination of CRP concentration and leukocyte count. Receiver operating characteristic (ROC) curves were constructed to analyse the predictive power and cut-points for time spent sitting and the presence of frailty.

Results: The areas under the ROC curves indicated that time spent sitting was an independent indicator of frailty (area under curve >0.6). The cut-off points for time spent sitting as an indicator of frailty were >257 min/day for men and >330 min/day for women.

Conclusions: Time spent sitting is associated with biomarkers of frailty in persons aged ≥60 years, indicating a need for interventions aimed at reducing sedentary behavior in this age group.

A general framework for the regression analysis of pooled biomarker assessments

As a cost-efficient data collection mechanism, the process of assaying pooled biospecimens is becoming increasingly common in epidemiological research; for example, pooling has been proposed for the purpose of evaluating the diagnostic efficacy of biological markers (biomarkers). To this end, several authors have proposed techniques that allow for the analysis of continuous pooled biomarker assessments. Regretfully, most of these techniques proceed under restrictive assumptions, are unable to account for the effects of measurement error, and fail to control for confounding variables. These limitations are understandably attributable to the complex structure that is inherent to measurements taken on pooled specimens. Consequently, in order to provide practitioners with the tools necessary to accurately and efficiently analyze pooled biomarker assessments, herein, a general Monte Carlo maximum likelihood-based procedure is presented. The proposed approach allows for the regression analysis of pooled data under practically all parametric models and can be used to directly account for the effects of measurement error. Through simulation, it is shown that the proposed approach can accurately and efficiently estimate all unknown parameters and is more computational efficient than existing techniques. This new methodology is further illustrated using monocyte chemotactic protein-1 data collected by the Collaborative Perinatal Project in an effort to assess the relationship between this chemokine and the risk of miscarriage. Copyright © 2017 John Wiley & Sons, Ltd.

Overweight, obesity, steps, and moderate to vigorous physical activity in children

OBJECTIVE

The objective of this study is to establish cutoff points for the number of steps/day and minutes/day of moderate to vigorous physical activity in relation to the risk of childhood overweight and obesity and their respective associations. In addition, we aim to identify the amount of steps/day needed to achieve the recommendation of moderate to vigorous physical activity in children from São Caetano do Sul.

METHODS

In total, 494 children have used an accelerometer to monitor steps/day and the intensity of physical activity (min/day). The moderate to vigorous physical activity has been categorized according to the public health recommendation (≤ 60 versus > 60 min/day). Overweight or obesity is defined as body mass index > +1 SD, based on reference data from the World Health Organization. The data on family income, education of parents, screen time, diet pattern, and sedentary time have been collected by questionnaires. Logistic regression and Receiver Operating Characteristic curves have been constructed.

RESULTS

On average, boys walked more steps/day (1,850) and performed more min/day of moderate to vigorous physical activity (23.1) than girls. Overall, 51.4% of the children have been classified as eutrophic and 48.6% as overweight or obese. Eutrophic boys walked 1,525 steps/day and performed 18.6 minutes/day more of moderate to vigorous physical activity than those with overweight/obesity (p < 0.05). The same has not been found in girls (p > 0.05). The cutoff points to prevent overweight and obesity in boys and girls were 10,500 and 8,500 steps/day and 66 and 46 min/day of moderate to vigorous physical activity, respectively. The walking of 9,700 steps/day for boys and 9,400 steps/day for girls ensures the scope of the recommendation of moderate to vigorous physical activity.

CONCLUSIONS

In boys, steps/day and moderate to vigorous physical activity have been negatively associated with body mass index, regardless of race, family income, education of parents, screen time, diet pattern, and sedentary time. We suggest, for steps/day and moderate to vigorous physical activity, studies with different ages and populations, with different designs, so as to inform the cause and effect relationship with various health parameters.

[Conicity index as a predictor of changes in the lipid profile of adolescents in a city in Northeast Brazil]

The objective was to evaluate the conicity index (C Index) as a predictor of changes in the lipid profile of adolescents and to establish its cutoff points. This was a cross-sectional study in 774 adolescents of both sexes (55% girls), 10 to 14 years of age. C Index was calculated according to the formula proposed by Valdez, considering body mass, height, and waist circumference (WC). Changes in the adolescents' lipid profile were defined according to one of the following conditions: elevated levels of total cholesterol, low-density lipoprotein (LDL), and triglycerides and low levels of high-density lipoprotein (HDL). The predictive power of the conicity index for altered lipid profile and its cutoff points were determined by Receiver Operating Characteristic (ROC) curves. The C Index was a good predictor of lipid alterations in adolescents, emphasizing triglycerides in boys 10 to 11 years of age (ROC = 0.67; 95%CI: 0.50-0.85) and 12 to 14 (ROC = 0.69; 95%CI: 0.59-0.80), and in girls 10 to 11 years (ROC = 0.65; 95%CI: 0.50-0.79); and LDL in girls 10 to 11 years (ROC = 0.70; 95%CI: 0.59-0.80) and boys (ROC = 0.65; 95%CI: 0.55-0.75) and girls (ROC = 0.62; 95%CI: 0.50-0.75) 12 to 14 years. The cutoff points for the C Index varied from 1.12 to 1.16 between boys and girls. The C Index can be used to predict lipid alterations, and its cutoff points can be used to screen adolescents for risk of alterations in lipid profile.

Evaluation of Cerebrospinal Fluid Assay Variability in Alzheimer's Disease

Studies of cerebrospinal fluid (CSF) biomarkers in Alzheimer's disease (AD) have indicated that much of the variability observed in the biomarkers may be due to measurement error. Biomarkers are often obtained with measurement error, which may make the diagnostic biomarker appear less effective than it truly is. In the Alzheimer's Disease Neuroimaging Initiative (ADNI) database, technical replicates of CSF biomarkers are available; the National Alzheimer's Coordinating Center database contains longitudinal replicates of CSF biomarkers. We focus on the area under the receiver operating characteristic curve (AUC) as the measure of diagnostic effectiveness for differentiating AD from normal cognition using CSF biomarkers and compare AUC estimates obtained by a more standard, naïve method (which uses a single observation per subject and ignores measurement error) to a maximum likelihood (ML) based method (which uses all replicates per subject and adjusts for measurement error). The choice of analysis method depends upon the noise to signal ratio (i.e., the magnitude of the measurement error variability relative to the true biomarker variability); moderate to high ratios may significantly bias the naïve AUC estimate, and the ML-based method would be preferred. The noise to signal ratios were low for the ADNI biomarkers but high for the tTau and pTau biomarkers in NACC. Correspondingly, the naïve and ML-based AUC estimates were nearly identical in the ADNI data but dissimilar for the tTau and pTau biomarkers in the NACC data. Therefore, using the naïve method is adequate for analysis of CSF biomarkers in the ADNI study, but the ML method is recommended for the NACC data.

Correcting AUC for Measurement Error

Diagnostic biomarkers are used frequently in epidemiologic and clinical work. The ability of a diagnostic biomarker to discriminate between subjects who develop disease (cases) and subjects who do not (controls) is often measured by the area under the receiver operating characteristic curve (AUC). The diagnostic biomarkers are usually measured with error. Ignoring measurement error can cause biased estimation of AUC, which results in misleading interpretation of the efficacy of a diagnostic biomarker. Several methods have been proposed to correct AUC for measurement error, most of which required the normality assumption for the distributions of diagnostic biomarkers. In this article, we propose a new method to correct AUC for measurement error and derive approximate confidence limits for the corrected AUC. The proposed method does not require the normality assumption. Both real data analyses and simulation studies show good performance of the proposed measurement error correction method.

Criminogenic factors, psychotic symptoms, and incident arrests among people with serious mental illnesses under intensive outpatient treatment

Although research robustly indicates that general or "criminogenic" factors predict various measures of recidivism, there is controversy about the extent to which these factors, versus untreated symptoms, lead to justice involvement for people with mental illnesses. Based on a sample of 183 people in intensive outpatient treatment followed for an average period of 34.5 months, the present study tested whether criminogenic factors (i.e., factor-analytically derived proxies of some of the "Central Eight"; Andrews & Bonta, 2010) and psychotic symptoms were independently associated with arrest. The study also compared the predictive utility of these domains. In the fully adjusted model, the antisocial subscale and male sex were associated with increased arrest rates, whereas psychosis and age were associated with decreased arrest rates. Criminogenic factors and psychotic symptoms had comparable predictive utility. We conclude that criminogenic factors-chiefly arrest history-and psychotic symptoms predict arrest rates. Both sets of variables appear useful for assessing risk of arrest among people with mental illnesses who are not under current correctional supervision.

Atividade física como discriminador da ausência de hipertensão arterial em homens adultos

Introdução: Diversos estudos epidemiológicos demonstram que a atividade física reduz a pressão arterial, porém a quantidade necessária para que estes benefícios sejam alcançados permanece especulativa.Objetivo: Analisar a quantidade (duração e intensidade) de atividade física em seus diferentes domínios (trabalho, deslocamento, atividade doméstica e tempo livre) como discriminador da ausência de hipertensão arterial em adultos do sexo masculino.Métodos: Estudo transversal realizado na cidade de Lauro de Freitas, Bahia, Brasil com amostra constituída por 220 indivíduos do sexo masculino com idade superior a 18 anos. Foram construídas diversas curvas Receiver Operating Characteristic (ROC) e comparadas às áreas sobre as mesmas entre a quantidade de atividade física em seus diferentes domínios e a ausência de hipertensão arterial. Verificou-se também a sensibilidade e especificidade para a quantidade de atividade física necessária para prevenção de hipertensão arterial. Foi utilizado o intervalo de confiança a 95%.Resultados: Entre os diferentes domínios de atividade física analisados encontrou-se maior significância estatística nas áreas sob a curva ROC para a atividade física no trabalho e no tempo livre. A caminhada não foi boa discriminadora para a ausência de hipertensão arterial em nenhum dos domínios analisados. Observou-se também que 180 min/semana de atividade física moderada, acumulada nos diferentes domínios foi o melhor ponto de corte para discriminar a ausência de hipertensão arterial.Conclusão: A prática da atividade física, principalmente de intensidade moderada, com duração de pelo menos 180 min/semana deve ser sugerida para indivíduos do sexo masculino visando contribuir para a prevenção da hipertensão arterial.

Anthropometry and physical activity level in the prediction of metabolic syndrome in children

OBJECTIVE

To evaluate the effectiveness of anthropometric measures and physical activity level in the prediction of metabolic syndrome (MetS) in children.

DESIGN

Cross-sectional study with children from public and private schools. Children underwent an anthropometric assessment, blood pressure measurement and biochemical evaluation of serum for determination of TAG, HDL-cholesterol and glucose. Physical activity level was calculated and number of steps per day obtained using a pedometer for seven consecutive days.

SETTING

Viçosa, south-eastern Brazil.

SUBJECTS

Boys and girls (n 187), mean age 9·90 (SD 0·7) years.

RESULTS

Conicity index, sum of four skinfolds, physical activity level and number of steps per day were accurate in predicting MetS in boys. Anthropometric indicators were accurate in predicting MetS for girls, specifically BMI, waist circumference measured at the narrowest point and at the level of the umbilicus, four skinfold thickness measures evaluated separately, the sum of subscapular and triceps skinfold thickness, the sum of four skinfolds and body fat percentage.

CONCLUSIONS

The sum of four skinfolds was the most accurate method in predicting MetS in both genders.

Mathematical modeling of area under the curve assessment criteria to quantify the antioxidant and pro-oxidant capacity: Coffee extracts as a case study

The development of a convenient mathematical application for testing the antioxidant and pro-oxidant capacity is essential in order to investigate potential sources of new agents and processes. In this regard, authors use the standardized values of the area under the curve of a kinetic profile of a dose-response agent, as a way to bypass the complex process of analyzing the kinetic variations of agents. In general, linear approaches are used, but such patterns frequently lead to unreliable results and misinterpretations, making it extremely difficult to compare the results from different assays. In this work, we have demonstrated the non-linearity of the dose-response area under the curve assessment criteria by means of simulations. A simple non-linear dose-response model was developed to describe the accurate response. As a case study, experimental data of extracts of unroasted coffee beans from five different country-climate locations for the two most common coffee varieties (Robusta and Arabica) were obtained using the β-carotene and crocin bleaching in vitro assays. Their antioxidant capacity was analyzed in detail and compared with commercial standards. The results show that the antioxidant capacity was greater than some of the commercial standards in terms of its maximum capacity, while when the analyses are based on rate parameters, the coffee extracts show between 6 and 40 times lower values than the standard antioxidants. In addition, to illustrate the advantages of using the standardized area units and the mathematical model developed, other more complex scenarios were recreated. We believe that the model application developed provides a simple alternative to summarize meaningful parameters that characterize the response, facilitates rigorous comparisons among the effects of different compounds and experimental approaches and helps to comprehend multi-variable scenarios.

Different waist circumference measurements and prediction of cardiovascular risk factors and metabolic syndrome in children

SUMMARY

OBJECTIVE

To compare the effectiveness of three waist circumference (WC) measurement sites to predict cardiovascular risk factors and metabolic syndrome (MS) in Brazilian children.

METHODS

187 children (mean age = 9.9 ± 0.7 years) were evaluated for weight, height, WC at three different sites: midpoint between the lower rib and iliac crest (WC1), umbilicus (WC2), and narrowest waist (WC3). Skinfolds (triceps and subscapular) and blood pressure were also measured. Analyses for triglycerides, HDL-C and glucose were carried out in 141 children.

RESULTS

For boys, the most accurate predictor of overweight and obesity (from body mass index, BMI) and low HDL-C levels was WC3, and for high percentage of body fat (from skinfolds) was WC1. For girls, WC2 was the most accurate predictor of MS, and hypertriglyceridemia, and for overweight and obesity, high body fat percentage, and low HDL-C levels, WC3 was the best predictor. WC1 was the most accurate in the prediction of high blood pressure.

CONCLUSIONS

Each WC measurement site was accurate in predicting cardiovascular risk factors and MS. However, our results indicate that WC3 was the best predictor of cardiovascular risk factors and MS in boys and girls.

Capacidade funcional como preditor de qualidade de vida na insuficiência cardíaca

INTRODUÇÃO: A insuficiência cardíaca (IC) prejudica a qualidade de vida (QV), enquanto a reabilitação cardiopulmonar e metabólica (RCPM) de pacientes com a síndrome proporciona melhora da capacidade funcional (CF) e da qualidade de vida. OBJETIVOS: Determinar a relação dos domínios da QV com a CF de pacientes com IC, assim como propor pontos de corte dos domínios da QV por meio da CF. MATERIAIS E MÉTODOS: Avaliou-se 57 pacientes com IC, classe funcional II e III, sendo 37 ingressantes (GI) no programa de RCPM e 20 participantes (GP) com mais de três meses de programa. A QV foi avaliada pelo questionário de Minnesota por meio dos domínios físicos, emocionais e dimensões gerais. A CF foi determinada por meio do teste de caminhada de seis minutos (TC6'), tendo pontos de corte definidos conforme proposto na literatura. Utilizou-se teste t de Student, correlação de Pearson e análise da curva ROC para responder aos objetivos da pesquisa, considerando significância de 5%. RESULTADOS: Participantes da RCPM apresentaram melhores escores da QV quando comparados aos ingressantes. Correlações significativas foram observadas entre o domínio emocional e TC6' para ambos os grupos. Verificou-se pontos de corte significativos dos domínios da QV advindos da CF, com destaque ao domínio emocional (sensibilidade/especificidade) para ambos os grupos. CONCLUSÃO: Os portadores de IC com mais de três meses de RCPM apresentaram melhor QV e capacidade funcional do que os iniciantes. O domínio emocional do questionário de Minnesota se mostrou um bom preditor de ponto de corte da capacidade funcional.

Association of neck circumference and obesity status with elevated blood pressure in children

High blood pressure (BP) and overweight/obesity are increasingly prevalent in children. We examined the associations of excess weight indicators including neck circumference (NC) and body mass index (BMI) with high BP in children. We hypothesized that high NC is associated with elevated BP. We utilized cross-sectional anthropometric and BP data on 1058 children aged 6-18 years. Patients were classified into weight and NC categories according to published guidelines. Prehypertension was defined as systolic or diastolic BP levels between 90th and 95th percentile for gender, age and height. Hypertension signifies systolic and/or diastolic BP levels ≥ 95th percentile for age, gender and height. The prevalence of elevated BP was 29.2% (prehypertension=10.1%, hypertension=19.1%). The prevalence of overweight and obesity was 19.0 and 18.7%, respectively. Rates of wide NC increased progressively with BMI categories by 8.8, 29.4 and 68.7% among normal weight, overweight and obese children, respectively. Within each BMI category, the unadjusted odds ratio for elevated BP was significantly higher in children with wide NC than those with normal NC (normal weight OR=1.78 (1.0-3.1), P=0.04); overweight OR=2.74 (1.5-5.2), P=0.001); obese OR=2.44 (1.3-4.6), P=0.006)). Increasing NC and BMI are associated with elevated BP in children. Joint presence of wide NC and high BMI is associated with significantly high rates of elevated BP. NC measurement may be a helpful tool to detect the presence of elevated BP in children.

Adjustment for measurement error in evaluating diagnostic biomarkers by using an internal reliability sample

Biomarkers are often measured with error due to imperfect lab conditions or temporal variability within subjects. Using an internal reliability sample of the biomarker, we develop a parametric bias-correction approach for estimating a variety of diagnostic performance measures including sensitivity, specificity, the Youden index with its associated optimal cut-point, positive and negative predictive values, and positive and negative diagnostic likelihood ratios when the biomarker is subject to measurement error. We derive the asymptotic properties of the proposed likelihood-based estimators and show that they are consistent and asymptotically normally distributed. We propose confidence intervals for these estimators and confidence bands for the receiver operating characteristic curve. We demonstrate through extensive simulations that the proposed approach removes the bias due to measurement error and outperforms the naïve approach (which ignores the measurement error) in both point and interval estimation. We also derive the asymptotic bias of naïve estimates and discuss conditions in which naïve estimates of the diagnostic measures are biased toward estimates produced when the biomarker is ineffective (i.e., when sensitivity equals 1 - specificity) or are anticonservatively biased. The proposed method has broad biomedical applications and is illustrated using a biomarker study in Alzheimer's disease. We recommend collecting an internal reliability sample during the biomarker discovery phase in order to adequately evaluate the performance of biomarkers with careful adjustment for measurement error.

[Level of physical activity in the prevention of excess visceral fat in postmenopausal women: how much is needed?]

OBJECTIVE

To analyze the level of physical activity (kcal/week) needed to prevent excess visceral fat in postmenopausal women.

SUBJECTS AND METHODS

The sample included 239 women with a mean age of 57.2 years. Visceral fat area (VFA) was measured by octopolar bioelectrical impedance, and physical activity, by the long version IPAQ. ROC Curves (Receiver Operating Characteristic) were drawn, and a 95% confidence interval was used.

RESULTS

The areas under the ROC curve for moderate physical activity and walk proved to be significant. Weekly expenditure of 1,601 kcal in walking, or 2,283 kcal in moderate physical activity were identified as good cutoff values to prevent excess VFA.

CONCLUSION

Mild to moderate physical activity, with a caloric expenditure between 1,601 and 2,283 kcal/week, prevents excess central adiposity in postmenopausal women.

Recalibration of the Gail model for predicting invasive breast cancer risk in Spanish women: a population-based cohort study

The Gail model for predicting the absolute risk of invasive breast cancer has been validated extensively in US populations, but its performance in the international setting remains uncertain. We evaluated the predictive accuracy of the Gail model in 54,649 Spanish women aged 45-68 years who were free of breast cancer at the 1996-1998 baseline mammographic examination in the population-based Navarre Breast Cancer Screening Program. Incident cases of invasive breast cancer and competing deaths were ascertained until the end of 2005 (average follow-up of 7.7 years) through linkage with population-based cancer and mortality registries. The Gail model was tested for calibration and discrimination in its original form and after recalibration to the lower breast cancer incidence and risk factor prevalence in the study cohort, and compared through cross-validation with a Navarre model fully developed from this cohort. The original Gail model overpredicted significantly the 835 cases of invasive breast cancer observed in the cohort (ratio of expected to observed cases 1.46, 95 % CI 1.36-1.56). The recalibrated Gail model was well calibrated overall (expected-to-observed ratio 1.00, 95 % CI 0.94-1.07), but it tended to underestimate risk for women in low-risk quintiles and to overestimate risk in high-risk quintiles (P = 0.01). The Navarre model showed good cross-validated calibration overall (expected-to-observed ratio 0.98, 95 % CI 0.92-1.05) and in different cohort subsets. The Navarre and Gail models had modest cross-validated discrimination indexes of 0.542 (95 % CI 0.521-0.564) and 0.544 (95 % CI 0.523-0.565), respectively. Although the original Gail model cannot be applied directly to populations with different underlying rates of invasive breast cancer, it can readily be recalibrated to provide unbiased estimates of absolute risk in such populations. Nevertheless, its limited discrimination ability at the individual level highlights the need to develop extended models with additional strong risk factors.

Is high body fat estimated by body mass index and waist circumference a predictor of hypertension in adults? A population-based study

BACKGROUND

The aim of this study was to assess the predictive capacity of body fat percentage (%BF) estimated by equations using body mass index (BMI) and waist circumference (WC) to identify hypertension and estimate measures of association between high %BF and hypertension in adults.

METHODS

This is a cross-sectional population-based study conducted with 1,720 adults (20-59 years) from Florianopolis, southern Brazil. The area under the ROC curve, sensitivity, specificity, predictive values, and likelihood ratios of cutoffs for %BF were calculated. The association between %BF and hypertension was analyzed using Poisson regression, estimating the unadjusted and adjusted prevalence ratios and 95% CI.

RESULTS

The %BF equations showed good discriminatory power for hypertension (area under the ROC curve > 0.50). Considering the entire sample, the cutoffs for %BF with better properties for screening hypertension were identified in the equation with BMI for men (%BF = 20.4) and with WC for women (%BF = 34.1). Adults with high %BF had a higher prevalence of hypertension.

CONCLUSIONS

The use of simple anthropometric measurements allowed identifying the %BF, diagnosing obesity, and screening people at risk of hypertension in order to refer them for more careful diagnostic evaluation.

Physical activity as an indicator of predictive functional disability in elderly

To analyze the time spent on physical activity in female and male individuals as a predictor of the absence of functional disability in older adults, a cross-sectional study was conducted with 624 individuals. Receiver Operating Characteristic curves (ROC) were constructed and compared to areas of physical activity by gender and the absence of functional disability. We identified cutoffs of physical activity (minutes / week) to predict the absence of functional disability (CI 95%). It was found that there is a higher area under the ROC curve for the time spent on physical activities in females. It was observed that 280 minutes / week (women) or 410 minutes / week (men) were the best cutoff points for predicting the absence of functional disability. Time spent on physical activity practices can serve as an important indicator to sort priority groups for certain interventions.

Gasto calórico dos diferentes domínios de atividade física como preditor da ausência de diabetes em adultos

INTRODUÇÃO: A atividade física apresenta efeito protetor contra doenças crônicas e fatores de risco cardiovascular; no entanto, o gasto calórico necessário para promover a prevenção do diabetes permanece especulativo. OBJETIVO: Analisar o gasto calórico dos diferentes domínios da atividade física (trabalho, deslocamento, atividade doméstica, tempo livre e atividade física total) como preditores da ausência de diabetes em adultos de ambos os sexos. MÉTODOS: Estudo transversal realizado na cidade de Lauro de Freitas, Bahia, Brasil (2007-2008) com amostra constituída por 522 indivíduos maiores de 18 anos, sendo 302 do sexo feminino e 220 do sexo masculino. Foram construídas curvas Receiver Operating Characteristic (ROC) e comparadas as áreas sob as mesmas, além de verificar-se a sensibilidade e especificidade para identificar os melhores pontos de corte entre os diferentes domínios da atividade física e a ausência de diabetes. Foi utilizado o intervalo de confiança a 95%. RESULTADOS: Entre os diferentes domínios de atividade física analisados encontrou-se significância estatística nas áreas sob a curva ROC para o tempo livre, deslocamento e para atividade física total. Observou-se também que o gasto calórico na atividade física total de 830kcal/semana quando analisados apenas os homens, e 1,774kcal/semana quando analisados homens e mulheres conjuntamente, foram os melhores pontos de corte para predizer a ausência de diabetes. CONCLUSÃO: A prática da atividade física deve ser sugerida em níveis adequados para indivíduos de ambos os sexos visando contribuir para a prevenção do diabetes.

Indicadores antropométricos de sobrepeso e obesidade como preditores de alterações lipídicas em adolescentes

OBJETIVO: Identificar o poder preditivo dos indicadores antropométricos de sobrepeso e obesidade para alterações lipídicas em adolescentes. MÉTODOS: Estudo transversal envolvendo 660 adolescentes de 14 a 19 anos (317 rapazes; 343 moças). Foram considerados os seguintes indicadores antropométricos: índice de massa corpórea (IMC), circunferência da cintura, razão cintura/estatura e índice de conicidade. As alterações lipídicas foram caracterizadas pelo colesterol total (CT) superior a 170mg/dL e lipoproteínas de alta densidade (HDL-C) inferiores a 45mg/dL. Para identificar os preditores das alterações lipídicas, adotou-se a análise das curvas Receiver Operating Characteristics (ROC). Foram calculados os pontos de corte com suas respectivas sensibilidades e especificidades e, posteriormente, as razões de prevalência entre os indicadores antropométricos e os desfechos investigados. RESULTADOS: As áreas sob as curvas ROC (intervalo de confiança de 95%) para CT elevado nos rapazes e respectivos pontos de corte foram: IMC de 0,74 (0,65-0,83) e 21,7kg/m²; circunferência de cintura de 0,73 (0,65-0,82) e 74cm; razão cintura/estatura de 0,72 (0,63-0,81) e 0,4; índice de conicidade de 0,60 (0,50-0,69) e 1,1. Para a predição dos baixos níveis de HDL-C, as áreas da curva ROC e os pontos de corte foram: IMC dos rapazes de 0,58 (0,52-0,64) e 20,7kg/m²; para as moças de 0,61 (0,53-0,69) e 20,8kg/m²; circunferência de cintura, rapazes com 0,57 (0,50-0,63) e 73,3cm, moças com 0,63 (0,55-0,72) e 71,5cm; razão cintura/estatura (C/Est), rapazes de 0,58 (0,52-0,65) e C/Est de 0,4, moças de 0,62 (0,54-0,70) e C/Est de 0,4; índice de conicidade, moças de 0,60 (0,51-0,68) e 1,1. CONCLUSÕES: Os indicadores antropométricos foram bons preditores de CT elevado nos rapazes e razoáveis para os baixos níveis de HDL-C para rapazes e moças.

Hybrid pooled-unpooled design for cost-efficient measurement of biomarkers

Evaluating biomarkers in epidemiological studies can be expensive and time consuming. Many investigators use techniques such as random sampling or pooling biospecimens in order to cut costs and save time on experiments. Commonly, analyses based on pooled data are strongly restricted by distributional assumptions that are challenging to validate because of the pooled biospecimens. Random sampling provides data that can be easily analyzed. However, random sampling methods are not optimal cost-efficient designs for estimating means. We propose and examine a cost-efficient hybrid design that involves taking a sample of both pooled and unpooled data in an optimal proportion in order to efficiently estimate the unknown parameters of the biomarker distribution. In addition, we find that this design can be used to estimate and account for different types of measurement and pooling error, without the need to collect validation data or repeated measurements. We show an example where application of the hybrid design leads to minimization of a given loss function based on variances of the estimators of the unknown parameters. Monte Carlo simulation and biomarker data from a study on coronary heart disease are used to demonstrate the proposed methodology.