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Concept: Percentile rank


BACKGROUND: The clinical course of Cystic Fibrosis (CF) is usually measured using the percent predicted FEV1 and BMI Z-score referenced against a healthy population, since achieving normality is the ultimate goal of CF care. Referencing against age and sex matched CF peers may provide valuable information for patients and for comparison between CF centers or populations. Here, we used a large database of European CF patients to compute CF specific reference equations for FEV1 and BMI, derived CF-specific percentile charts and compared these European data to their nearest international equivalents. METHODS: 34859 FEV1 and 40947 BMI observations were used to compute European CF specific percentiles. Quantile regression was applied to raw measurements as a function of sex, age and height. Results were compared with the North American equivalent for FEV1 and with the WHO 2007 normative values for BMI. RESULTS: FEV1 and BMI percentiles illustrated the large variability between CF patients receiving the best current care. The European CF specific percentiles for FEV1 were significantly different from those in the USA from an earlier era, with higher lung function in Europe. The CF specific percentiles for BMI declined relative to the WHO standard in older children. Lung function and BMI were similar in the two largest contributing European Countries (France and Germany). CONCLUSION: The CF specific percentile approach applied to FEV1 and BMI allows referencing patients with respect to their peers. These data allow peer to peer and population comparisons in CF patients.

Concepts: Median, Quantile, Cystic fibrosis, Peer-to-peer, Quartile, Reference, Percentile rank, File sharing


Objective The objective of this study was to use two-dimensional (2D) ultrasound (US) during routine prenatal surveillance to develop normative estimated placental volume (EPV) growth curves.Study Design Patients ≥ 18 years old with singleton pregnancies were prospectively followed from 11 weeks gestational age (GA) until delivery. At routine US visits, placental width, height, and thickness were measured and EPV calculated using a validated mathematical model.Results In this study, 423 patients were scanned between 9.7 and 39.3 weeks GA to generate a total of 627 EPV calculations. Readings were clustered at 12 and 20 weeks, times of routine scanning. The mean EPV was 73 ± 47 cc at 12.5 ± 1.5 weeks (n = 444) and 276 ± 106 cc at 20 ± 2 weeks (n = 151). The data best fit a parabolic function as follows: EPV = (0.384GA - 0.00366GA2)3. Tenth and 90th percentile lines were generated with ± 1.28 SE offset. EPV readings below the 10th or above the 90th percentiles tended to be associated with either small or large newborns, respectively.Conclusion Routine 2D US created EPV growth curves, which may be useful for stratifying patients into prenatal risk groups.

Concepts: Pregnancy, Childbirth, Mathematics, Embryo, Fetus, Obstetrics, Gestational age, Percentile rank


One is inclined to conceptualize impact in terms of citations per publication, and thus as an average. However, citation distributions are skewed, and the average has the disadvantage that the number of publications is used in the denominator. Using hundred percentiles, one can integrate the normalized citation curve and develop an indicator that can be compared across document sets because percentile ranks are defined at the article level. I apply this indicator to the set of 58 journals in the WoS Subject Category of “Nanoscience & nanotechnology,” and rank journals, countries, cities, and institutes using non-parametric statistics. The significance levels of results can thus be indicated. The results are first compared with the ISI-impact factors, but this Integrated Impact Indicator (I3) can be used with any set downloaded from the (Social) Science Citation Index. The software is made publicly available at the Internet. Visualization techniques are also specified for evaluation by positioning institutes on Google Map overlays.

Concepts: Median, Academic publishing, Non-parametric statistics, Ranking, Science Citation Index, Bibliometrics, Google, Percentile rank


There is little information regarding age-related reference intervals (RIs) of carotid-femoral pulse wave velocity (cfPWV) for large healthy populations in South America. The aims of this study were to determine cfPWV RIs and percentiles in a cohort of healthy children, adolescents, and adults and to generate year-to-year percentile curves and body-height percentile curves for children and adolescents. cfPWV was measured in 1722 healthy participants with no cardiovascular risk factors (9-87 years, 60% men). First, RIs were evaluated for males and females through correlation and covariate analysis. Then, mean and standard deviation age-related equations were obtained for cfPWV using parametric regression methods based on fractional polynomials and age-specific (year-to-year) percentile curves that were defined using the standard normal distribution. Age-specific first, 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, 97.5th, and 99th percentile curves were calculated. Finally, height-related cfPWV percentile curves for children and adolescents (<21 years) were established. After adjusting for age and blood pressure differences with respect to females, males showed higher cfPWV levels (6.60 vs 6.45 m/s; P < .01). Thus, specific RIs for males and females were reported. The study provides the largest database to date concerning cfPWV in healthy people from Argentina. Specific RIs and percentiles of cfPWV are now available according to age and sex. Specific percentiles of cfPWV according to body height were reported for people younger than 21 years.

Concepts: Variance, Median, Normal distribution, Standard deviation, Cauchy distribution, Percentile rank, Log-normal distribution, Error function


Age-related reference intervals (RIs) of aortic pulse wave velocity (Ao-PWV) obtained from a large healthy population are lacking in South America. The aims of this study were to determine Ao-PWV RIs in a cohort of healthy children and adolescents from Argentina and to generate year-to-year percentile curves. Ao-PWV was measured in 1000 healthy subjects non-exposed to traditional cardiovascular risk factors (Age: 10-22 y. o., 56% males). First, we evaluated if RIs for males and females were necessaries (correlation and covariate analysis). Second, mean (M) and standard deviation (SD) age-related equations were obtained for cf-PWV, using parametric regression methods based on fractional polynomials. Third, age-specific (year to year) percentiles curves (for all, males and females children and adolescents) were generated using the standard normal distribution. They were, age-specific 1st, 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, 97.5th and 99th percentile curves and values. After covariate analysis (i.e., adjusting by age, jugulum-symphysis distance, body weight and height), specific RIs for males and females of children and adolescents were evidenced as necessaries. The equations were For all subjects: Ao-PWV_Mean = 4.98 + 12.86x10-5Age3. Ao-PWV_SD = 0.47 + 21.00x10-6Age3. For girls: Ao-PWV_Mean = 5.07 + 10.23x10-5Age3. Ao-PWV_SD = 0.50 + 10.00x10-6Age3. For boys: Ao-PWV_Mean = 4.87 + 15.81x10-5Age3. Ao-PWV_SD = 0.46 + 22.34x10-6Age3. Our study provides the largest database to-date concerning Ao-PWV in healthy children and adolescents in Argentina. Age-related equations (M and SD values) for Ao-PWV are reported by the first time. Specific RIs and percentiles of Ao-PWV are now available according to age and sex for an Argentinian population.

Concepts: Variance, Median, Normal distribution, Standard deviation, Cauchy distribution, Percentile rank, Log-normal distribution, Error function


Despite decades of research, the concept of normality in labour in terms of its progression and duration is not universal or standardized. However, in clinical practice, it is important to define the boundaries that distinguish what is normal from what is abnormal to enable women and care providers have a shared understanding of what to expect and when labour interventions are justified.

Concepts: Pregnancy, Childbirth, Clinical trial, Normal distribution, Standard deviation, Kernel, Percentile rank


The Advanced Reach Tool V1.5 (ART) is a mathematical model for occupational exposures conceptually based on, but implemented differently than, the “classic” Near Field/Far Field (NF/FF) exposure model. The NF/FF model conceptualizes two distinct exposure “zones”; the near field, within approximately 1m of the breathing zone, and the far field, consisting of the rest of the room in which the exposure occurs. ART has been reported to provide “realistic and reasonable worst case” estimates of the exposure distribution. In this study, benzene exposure during the use of a metal parts washer was modeled using ART V1.5, and compared to actual measured workers samples and to NF/FF model results from three previous studies. Next, the exposure concentrations expected to be exceeded 25%, 10% and 5% of the time for the exposure scenario were calculated using ART. Lastly, ART exposure estimates were compared with and without Bayesian adjustment. The modeled parts washing benzene exposure scenario included distinct tasks, e.g. spraying, brushing, rinsing and soaking/drying. Because ART can directly incorporate specific types of tasks that are part of the exposure scenario, the present analysis identified each task’s determinants of exposure and performance time, thus extending the work of the previous three studies where the process of parts washing was modeled as one event. The ART 50th percentile exposure estimate for benzene (0.425ppm) more closely approximated the reported measured mean value of 0.50ppm than the NF/FF model estimates of 0.33ppm, 0.070ppm or 0.2ppm obtained from other modeling studies of this exposure scenario. The ART model with the Bayesian analysis provided the closest estimate to the measured value (0.50ppm). ART (with Bayesian adjustment) was then used to assess the 75th, the 90th and 95th percentile exposures, predicting that on randomly selected days during this parts washing exposure scenario, 25% of the benzene exposures would be above 0.70ppm; 10% above 0.95ppm; and 5% above 1.15ppm. These exposure estimates at the three different percentiles of the ART exposure distribution refer to the modeled exposure scenario not a specific workplace or worker. This study provides a detailed comparison of modeling tools currently available to occupational hygienists and other exposure assessors. Possible applications are considered.

Concepts: Mathematics, Decile, Percentile, Median, Quantile, Mean, Quartile, Percentile rank


Abdominal obesity is even a stronger risk factor than overall obesity for noncommunicable chronic diseases. We examined the association between smoking and abdominal obesity among adolescents. Analyses were based on 38,813 subjects aged 15-17 years from the Study of Cardiovascular Risks in Adolescents (ERICA), a Brazilian school-based national survey. Abdominal obesity was defined considering waist circumference (WC) percentiles. Statistical analyses, stratified by sex, considered the sample complex design. Poisson regression with robust variance was used to estimate smoker-to-nonsmoker abdominal obesity prevalence ratio (PR), adjusting by sociodemographic and lifestyle variables. Higher prevalence of abdominal obesity was observed among adolescents who consumed >1 cigarettes/day, comparing to nonsmokers: considering WC >80th percentile, adjusted-PR for boys was 1.27 [95%CI:1.05,1.52] and, for girls, 1.09 [95%CI:1.00,1.19]; using the 90th percentile, adjusted-PR were 2.24 [95%CI:1.70,2.94] and 1.27 [95%CI:1.12,1.46], respectively for male and female adolescents. Our findings suggest a positive association between cigarette consumption and the prevalence of abdominal obesity, for both boys and girls. Although other studies had found this association in adults, our study contributes to this discussion by assessing it in adolescents using a nationwide representative sample of medium and large municipalities.

Concepts: Regression analysis, Male, Statistics, Female, Risk, Cigarette, Sex, Percentile rank


Reference values and the characteristics of the electrocardiographic (ECG) findings using a large number of subjects are lacking for children and adolescents.Methods and Results:A total of 56,753 digitally stored ECGs of participants in a school-based ECG screening system were obtained between 2006 and 2009 in Kagoshima, Japan. Each ECG was manually reviewed by 2 pediatric cardiologists and only ECGs with sinus rhythm were included. A final total of 48,401 ECGs from 16,773 1st (6 years old, 50% girls), 18,126 7th (12 years old, 51% girls), and 13,502 10th graders (15 years old, 52% girls) were selected. ECG variables showed differences in age and sex. However, the effects of age and sex on ECG variables such as the PQ interval, QRS voltage, and STJ segment were also different. The 98th percentile values of well-known surrogate parameters for ventricular hypertrophy in the present study were much higher than the conventional criteria.

Concepts: Present, Cardiology, Median, Ventricular fibrillation, Electrocardiography, Percentile rank, Holter monitor, QRS complex


To illustrate the difficulties in optimal growth monitoring of children with severe obesity or underweight by using the Centers for Disease Control and Prevention (CDC) 2000 age- and sex-specific BMI percentile growth charts. We also aimed to examine the utility of a new modified CDC BMI z score chart to monitor growth in children with normal and extreme BMI percentiles by using real-life clinical scenarios.

Concepts: Cancer, Nutrition, Obesity, Body mass index, Body shape, Percentile rank