Percentile Estimates Research Articles

Could masking gestational age estimation during scanning improve detection of small-for-gestational-age fetuses? A controlled pre–post evaluation

Antenatal detection of small-for-gestational-age fetuses improves outcomes and reduces perinatal mortality rates. However, ultrasonographic estimation of fetal weight is subject to several potential sources of error. One potential source of error is subconscious operator bias towards "normal" measurement values for gestational age (observer-expectancy bias). We aimed to determine whether the sensitivity of small-for-gestational-age detection is improved by removing real-time display of estimated gestational age during measurement of the abdominal circumference in the third trimester. This retrospective evaluation (November 2014-May 2018 inclusive) included all singleton infants liveborn at ≥28 weeks gestation in a single United Kingdom obstetrics center. In the preintervention phase, real-time estimated gestational age was displayed to sonographers as they measured fetal abdominal circumference (the key determinant of estimated fetal weight with the use of the INTERGROWTH 21st fetal weight equation) in the third trimester. In the postintervention phase, real-time gestational age information was removed on selected ultrasound machines. Accuracy of birthweight percentile estimation was assessed before and after intervention, both in the full cohort comprising all eligible scans and in a subcohort that was scanned within 4 weeks of delivery. We assessed the accuracy of small-for-gestational-age detection using the sensitivity, positive likelihood ratio, and area under the receiver-operator curve. Of the 18,342 eligible pregnancies, 9342 (51%) had a third-trimester growth scan. The sensitivity of ultrasonographic estimation of fetal weight for antenatal detection of small-for-gestational-age babies did not change significantly between the before and after intervention phases (31.5% confidence interval, 27.1-36.2 vs 31.7% confidence interval, 20.2-45.0). Although the sensitivity for small-for-gestational-age detection was higher in the subcohort that was scanned within 4 weeks of delivery than in the full cohort (P<.001), there was no significant difference between the before and after intervention phases (58% confidence interval, 50-66 vs 65% confidence interval, 43-84). With the use of an estimation of the abdominal circumference percentile rather than estimated fetal weight percentile significantly decreased the sensitivity for small-for-gestational-age detection in all groups (P<.01), but there was no difference between the before and after intervention phases. Blinding operators to the estimated gestation of the fetus during abdominal circumference measurement does not significantly alter the antenatal detection rate of small-for-gestational-age babies. The observer-expectancy effect is therefore unlikely to be a significant contributor to the error that is associated with ultrasonographic estimation of fetal weight.

Biomonitoring of mercury and persistent organic pollutants in Michigan urban anglers and association with fish consumption.

The 32-mile Detroit River and surrounding tributaries have been designated as a Great Lakes Area of Concern due to pollution from decades of municipal and industrial discharges, sewer overflows and urban development. Key pollutants in fish samples from the Detroit River include mercury, polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), dioxins and furans. A biomonitoring study was conducted to assess exposures to these persistent toxic substances in Detroit urban shoreline anglers who may be at high exposure risk due to consumption of locally caught fish. Using a modified venue-based sampling approach, 287 adult shoreline anglers along the Detroit River were recruited and participated in the program. Study participants provided blood and urine specimens and completed a questionnaire following informed consent. We examined percentile estimates for total blood mercury, PCBs, DDE, and dioxin-like total toxic equivalency (TEQ) concentrations among study participants. Multiple linear regression was used to identify important predictors of contaminant concentrations. Participants consumed a median of 64 Detroit River caught fish meals in the past year. The Detroit urban anglers' median total blood mercury concentrations was 3.2 times higher than that for the general adult U.S. population. PCB concentrations among the Detroit anglers aged 18-39 years were higher than the U.S. population of the same race/ethnicity. Elevated levels of DDE and total TEQ concentrations were not observed in the cohort. Eating more locally caught fish was associated with higher total blood mercury and serum PCB concentrations. The biomonitoring data served to inform public health officials and help guide environmental public health actions to reduce harmful exposures.

Methods and applications of percentile estimation

ABSTRACT Percentile is ubiquitous in statistics and plays a significant role in the day-to-day statistical application. FDA Guidance for Industry: Assay Development for Immunogenicity Testing of Therapeutic Protein Products (2016) recommends the use of a lower confidence limit of the percentile of the negative subject population as the cut point to guarantee a pre-specified false-positive rate with high confidence. Shen proposed and compared an exact t approach with some approximated approaches. However, the exact t approach might be compromised by computational time and complexity. In this article, we proposed to use a UMOVER method as a potential alternative for percentile estimation for one application to screening and confirmatory cut point determination due to its easy implementation and similar performance to the exact t approach. The applications and performance comparison with different approaches are investigated and discussed. Furthermore, we extended the proposed method for the comparison of the percentile of the test product and percentile of the reference product followed by numerical studies.

Non-fasting bioelectrical impedance analysis in cystic fibrosis: Implications for clinical practice and research

BackgroundNutritional status affects pulmonary function in cystic fibrosis (CF) patients and can be monitored by using bioelectrical impedance analysis (BIA). BIA measurements are commonly performed in the fasting state, which is burdensome for patients. We investigated whether fasting is necessary for clinical practice and research. MethodsFat free mass (FFM) and fat mass (FM) were determined in adult CF patients (n = 84) by whole body single frequency BIA (Bodystat 500) in a fasting and non-fasting state. Fasting and non-fasting BIA outcomes were compared with Bland-Altman plots. Pulmonary function was expressed as Forced Expiratory Volume at 1 s percentage predicted (FEV1%pred). Comparability of the associations between fasting and non-fasting body composition measurements with FEV1%pred was assessed by multiple linear regression. ResultsFasting FFM, its index (FFMI), and phase angle were significantly lower than non-fasting estimates (−0.23 kg, p = 0.006, −0.07 kg/m2, p = 0.002, −0.10°, p = 0.000, respectively). Fasting FM and its index (FMI) were significantly higher than non-fasting estimates (0.22 kg, p = 0.008) 0.32%, p = 0.005, and 0.07 kg/m2, (p = 0.005). Differences between fasting and non-fasting FFM and FM were <1 kg in 86% of the patients. FFMI percentile estimates remained similar in 83% of the patients when measured after nutritional intake. Fasting and non-fasting FFMI showed similar associations with FEV1%pred (β: 4.3%, 95% CL: 0.98, 7.70 and β: 4.6%, 95% CI: 1.22, 8.00, respectively). ConclusionDifferences between fasting and non-fasting FFM and FM were not clinically relevant, and associations with pulmonary function remained similar. Therefore, BIA measurements can be performed in a non-fasting state.

Age-specific norms and validation of the German SDQ parent version based on a nationally representative sample (KiGGS).

The Strengths and Difficulties Questionnaire (SDQ) is the most widely used mental health screening instrument for children and adolescents. It is a short questionnaire including 25 items that can be answered by parents, teachers or children. There are two studies which report norms for the German SDQ parent version. They do not include children younger than 6years. Moreover, whether the German SDQ parent version is measurement invariant across age has not yet been investigated. The absence of measurement invariance across age would support the use of age-specific norms that are not yet available for the German SDQ parent version. We used data of the German Health Interview and Examination Survey for Children and Adolescents (KiGGS), a nationally representative survey including 14,835 children aged 3-17years, to assess measurement invariance of the German SDQ parent version across the full age range. Multi-group confirmatory factor analysis revealed that the hyperactivity and emotional symptoms subscales are not comparable between children of different ages. This supports the use of age-specific norms for these two subscales and for the total SDQ. We used methods of centile estimation to smoothly model the centiles of the SDQ totalscore and the subscale scores in dependence on age. These age-specific centiles reflect the developmental course of SDQ problems in children (including preschoolers) and adolescents living in Germany. They can be used to identify children and adolescents with abnormal behaviour, while accounting for the developmental course of emotional and behaviour problems.

Importance of details in food descriptions in estimating population nutrient intake distributions

BackgroundNational food consumption surveys are important policy instruments that could monitor food consumption of a certain population. To be used for multiple purposes, this type of survey usually collects comprehensive food information using dietary assessment methods like 24-h dietary recalls (24HRs). However, the collection and handling of such detailed information require tremendous efforts. We aimed to improve the efficiency of data collection and handling in 24HRs, by identifying less important characteristics of food descriptions (facets) and assessing the impact of disregarding them on energy and nutrient intake distributions.MethodsIn the Dutch National Food Consumption Survey 2007–2010, food consumption data were collected through interviewer-administered 24HRs using GloboDiet software in 3819 persons. Interviewers asked participants about the characteristics of each food item according to applicable facets. Food consumption data were subsequently linked to the food composition database. The importance of facets for predicting energy and each of the 33 nutrients was estimated using the random forest algorithm. Then a simulation study was performed to determine the influence of deleting less important facets on population nutrient intake distributions.ResultsWe identified 35% facets as unimportant and deleted them from the total food consumption database. The majority (79.4%) of the percent difference between percentile estimates of the population nutrient intake distributions before and after facet deletion ranged from 0 to 1%, while 20% cases ranged from 1 to 5% and 0.6% cases more than 10%.ConclusionWe concluded that our procedure was successful in identifying less important food descriptions in estimating population nutrient intake distributions. The reduction in food descriptions has the potential to reduce the time needed for conducting interviews and data handling while maintaining the data quality of the survey.

Hippocampal volume across age: Nomograms derived from over 19,700 people in UK Biobank.

Measurement of hippocampal volume has proven useful to diagnose and track progression in several brain disorders, most notably in Alzheimer's disease (AD). For example, an objective evaluation of a patient's hippocampal volume status may provide important information that can assist diagnosis or risk stratification of AD. However, clinicians and researchers require access to age-related normative percentiles to reliably categorise a patient's hippocampal volume as being pathologically small. Here we analysed effects of age, sex, and hemisphere on the hippocampus and neighbouring temporal lobe volumes, in 19,793 generally healthy participants in the UK Biobank. A key finding of the current study is a significant acceleration in the rate of hippocampal volume loss in middle age, more pronounced in females than in males. In this report, we provide normative values for hippocampal and total grey matter volume as a function of age for reference in clinical and research settings. These normative values may be used in combination with our online, automated percentile estimation tool to provide a rapid, objective evaluation of an individual's hippocampal volume status. The data provide a large-scale normative database to facilitate easy age-adjusted determination of where an individual hippocampal and temporal lobe volume lies within the normal distribution.

Evaluation of Exposure Assessment Tools under REACH: Part II-Higher Tier Tools.

Stoffenmanager®v4.5 and Advanced REACH Tool (ART) v1.5, two higher tier exposure assessment tools for use under REACH, were evaluated by determining accuracy and robustness. A total of 282 exposure measurements from 51 exposure situations (ESs) were collected and categorized by exposure category. In this study, only the results of liquids with vapor pressure (VP) > 10 Pa category having a sufficient number of exposure measurements (n = 251 with 42 ESs) were utilized. In addition, the results were presented by handling/activity description and input parameters for the same exposure category. It should be noted that the performance results of Stoffenmanager and ART in this study cannot be directly compared for some ESs because ART allows a combination of up to four subtasks (and nonexposed periods) to be included, whereas the database for Stoffenmanager, separately developed under the permission of the legal owner of Stoffenmanager, permits the use of only one task to predict exposure estimates. Thus, it would be most appropriate to compare full-shift measurements against ART predictions (full shift including nonexposed periods) and task-based measurements against task-based Stoffenmanager predictions. For liquids with VP > 10 Pa category, Stoffenmanager®v4.5 appeared to be reasonably accurate and robust when predicting exposures [percentage of measurements exceeding the tool's 90th percentile estimate (%M > T) was 15%]. Areas that could potentially be improved include ESs involving the task of handling of liquids on large surfaces or large work pieces, allocation of high and medium VP inputs, and absence of local exhaust ventilation input. Although the ART's median predictions appeared to be reasonably accurate for liquids with VP > 10 Pa, the %M > T for the 90th percentile estimates was 41%, indicating that variance in exposure levels is underestimated by ART. The %M > T using the estimates of the upper value of 90% confidence interval (CI) of the 90th percentile estimate (UCI90) was considerably reduced to 18% for liquids with VP > 10 Pa. On the basis of this observation, users might be to consider using the upper limit value of 90% CI of the 90th percentile estimate for predicting reasonable worst case situations. Nevertheless, for some activities and input parameters, ART still shows areas to be improved. Hence, it is suggested that ART developers review the assumptions in relation to exposure variability within the tool, toward improving the tool performance in estimating percentile exposure levels. In addition, for both tools, only some handling/activity descriptions and input parameters were considered. Thus, further validation studies are still necessary.

The Volume of Gas Hydrate‐Bound Gas in the Northern Gulf of Mexico

AbstractThe northern Gulf of Mexico is known to host gas hydrate in submarine sediments. Estimating the amount of gas hydrate for both carbon cycle and resource interest has been ongoing for more than three decades. A large range of estimates (from 0.2 to 680 trillion cubic meters (TCM)) for hydrate‐bound natural gas at standard temperature and pressure exists. We bring a new perspective to resource estimates by using ~800 publicly available petroleum industry well logs assessed for natural gas hydrate. Our resulting probabilistic range of the gas hydrate‐bound natural gas in the northern Gulf of Mexico ranges from 37 TCM (10th percentile estimate) to 78 TCM (90th percentile estimate) of gas hydrate‐bound natural gas, with a mean estimate of 56 TCM. This suggests that the gas hydrate resource density of the northern Gulf of Mexico is 4 times lower than that previously estimated by the Bureau of Ocean Energy Management. Our results also indicate that over half of the gas hydrate in the area is strategically hosted in sand reservoirs, which is significantly higher than that previously estimated.

Histogram Analysis of Adrenal Lesions With a Single Measurement for 10th Percentile: Feasibility and Incremental Value for Diagnosing Adenomas.

Our purpose was to assess whether histogram analysis of adrenal lesions from a single measurement of mean attenuation and SD, using a threshold of 10% of negative voxels, can replace voxel counting while maintaining diagnostic accuracy. In a 4-year period, 325 adrenal lesions were detected on CT examinations of 308 consecutive patients. After exclusions, 91 patients with 108 lesions, including 20 malignant lesions and 88 adenomas (defined by histologic results or follow-up), were enrolled. Two observers retrospectively measured lesion size, mean attenuation value, and SD attenuation value and generated a pixel histogram. The 10th percentile (P10) was obtained from the conventional histogram analysis and was also calculated from the following formula: P10 = mean attenuation - (1.282 × SD). Diagnostic accuracies of the mean attenuation criterion, histogram analysis, and calculated 10th percentile were compared. The study group was composed of 74 patients with 88 adenomas and 17 patients with 20 malignant lesions, including seven adrenocortical carcinomas and 13 metastases; 93.1% of histograms showed normal distribution. The correlation between histogram analysis and calculated 10th percentile was 0.9827 and 0.9843 for reader 1 and 2 (p < 0.00001 for both). For both readers, sensitivity and specificity of the mean attenuation analysis were 65.9% (95% CI, 55.0-75.7%) and 100.0% (95% CI, 83.2-100%). The sensitivity and specificity of histogram analysis and calculated 10th percentile were the same, 87.5% (95% CI, 78.7-93.6%) and 95.0% (95% CI, 75.1-99.8%), for both readers. The increment increase in sensitivity was significant (p < 0.001), whereas the decrease in specificity was not (p = 0.15). For most adrenal lesions, the pixel attenuation has a gaussian distribution, allowing estimation of 10th percentile with a single measurement. The accuracy of histogram analysis and calculated 10th percentile outperformed the mean attenuation as a diagnostic criterion for nonfunctioning adenomas.

On confidence interval estimation of normal percentiles

Chakraborti and Li (Am Stat 61:331–336, 2007) considered several methods for confidence interval estimation of a normal distribution percentile. In this paper, we comment on two of their methods based on maximum likelihood and Bayesian inference. We show that the use of some approximations and simulations in the two methods is not necessary and some improvements and modifications can be made. Also, we compare the modified methods with methods in Chakraborti and Li (2007).

The Precision and Accuracy of Urinary Creatinine Analysis for Correction of Urine Dilution in Biological Monitoring Measurements

Biomonitoring has been widely used to assess environmental exposure, and spot urine is commonly studied due to its easy sample collection. The variability of urine dilution has been crucial for assessing the exposure magnitude. Previous studies indicated that creatinine-adjusted concentrations are better correlated with the parent chemical concentrations in blood, plasma or serum than unadjusted concentrations. More recent studies have documented problems with creatinine-adjustment in pregnant women and diverse populations because creatinine varies with age, gender, race, body size, and diet.In addition to the inter- and intra-person variability in creatinine, we found significant variability in the testing methods and the testing laboratories. Two immunoassays gave decidedly different concentrations on the same samples in two different laboratories and even had a greater than 35% bias on NIST Standard Reference Materials. In an attempt to standardize the creatinine measurements, both laboratories adopted the same immunoassay.The inter-laboratory relative percent differences (RPD) ranged from 0.3-13.4% with 5.2% median, and the values determined in each laboratory were highly correlated (Pearson correlation coefficient: r&amp;#61;0.98). Although the results were correlated and relatively precise, 15% biases were found between laboratories with values determined by laboratory B being uniformly higher. The directional significant differences were confirmed by paired t-test (p-value&amp;lt;0.001). Thus, a systemic error can occur among different laboratories which might alter the point estimates of central tendency and percentile concentrations.The results show that in addition to the inherent limitations of biological variation in using creatinine-adjustment in biomonitoring, laboratory error from non-standardized measurements can further introduce variation. Taken together, we suggest that the standardized creatinine measurement or cross-laboratories validation is needed.

Biomonitoring of Mercury and Persistent Organic Pollutants in Michigan Urban Anglers and Association with Fish Consumption

The 32-mile Detroit River and surrounding tributaries have been designated as a Great Lakes Area of Concern due to pollution from decades of municipal and industrial discharges, sewer overflows and urban development. Key pollutants in fish samples from the Detroit River include mercury, polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), dioxins and furans. A biomonitoring study was conducted to assess exposures to these persistent toxic substances in Detroit urban anglers who may be at higher exposure risk due to consumption of locally caught fish. Using a modified venue-based sampling approach, 287 adult shoreline anglers along the Detroit River were recruited and participated in the program. Study participants provided blood and urine specimens and completed a questionnaire interview. We examined percentile estimates for total blood mercury, PCBs, DDE, and dioxin-like total toxic equivalency (TEQ) concentrations among study participants compared with the general U.S. population. Multiple linear regression was used to identify important predictors of contaminant concentrations. Quantile regression was used to investigate whether eating locally caught fish had a differential effect at various quantiles of each contaminant. Participants reported eating an average of 20 Detroit River caught fish meals in the past year. The Detroit urban anglers&amp;#8217; total blood mercury and PCB concentrations were 2 to 3 times higher than the general U.S. population. Elevated levels of DDE and total TEQ concentrations were not observed in the cohort. Eating more locally caught fish was associated with higher total blood mercury and serum PCB concentrations, and this effect had a larger impact at higher quantiles of these biomarkers. The biomonitoring data served to inform public health officials and guide state and local public health actions to reduce harmful exposures.

The best single-observational and two-observational percentile estimations in the exponentiated Weibull-geometric distribution compared with maximum likelihood and percentile estimations

In this research the best single-observation percentile estimation (BSPE) and best two-observation percentile estimation (BTPE), are introduced. Then theses estimators are obtained for probability density function and cumulative distribution function of the exponentiated Weibull-geometric (EWG) with increasing, decreasing, bathtub and unimodal shaped failure rate function. Finally, these estimators are compared with the maximum likelihood (ML) and percentile (PC) estimations using the Monte Carlo simulation and a real data set.

Erratum

The Journal of Wildlife ManagementVolume 82, Issue 8 p. 1808-1808 ErratumFree Access Erratum This article corrects the following: Greater sage-grouse population trends across Wyoming David R. Edmunds, Cameron L. Aldridge, Michael S. O'Donnell, Adrian P. Monroe, Volume 82Issue 2The Journal of Wildlife Management pages: 397-412 First Published online: October 27, 2017 First published: 10 September 2018 https://doi.org/10.1002/jwmg.21560Citations: 3AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Edmunds, D. R., C. L. Aldridge, M. S. O'Donnell, and A. P. Monroe. 2018. Greater sage-grouse population trends across Wyoming. Journal of Wildlife Management 82:397–412. In this article, we calculated the intrinsic per capita rate of growth (r; Dennis et al. 1991, Morris and Doak 2002), which we then transformed to the finite rate of population growth (λ) based on the conversion λ = er (Case 2000, Mills 2013). However, we made an error in the reporting of λ for several models, including reporting the density-dependent effect for the Ricker (Ricker 1954, Dennis and Taper 1994) and Gompertz (Jacobson et al. 2004) models rather than the overall λ estimate. We also reported the difference in λ between trend and numbered intervals for the period effects models rather than the average of the λ estimates across intervals. These errors resulted from reporting the incorrect model coefficients from the generalized linear model (glm) output and resulted in values that were less than the λ estimates in most cases but did not alter our primary conclusion that fine-scale population trends may differ from large-scale trends. The authors regret these errors. These 2 errors resulted in incorrect λ estimates reported in tables 1–4, S1, and S3–S7, and shown in figures 3–6. The errors were embedded within the output reporting of our program R code provided in table S2. We have corrected all of the affected text, tables, and figures (see Supporting Information A, available online), including correcting the R code to create the proper output and all other material that was in the original Supporting Information (see Supporting Information B, available online). When we fixed the reporting error for the density-dependent models, including the Gompertz and Ricker models with and without period effects terms, we realized it was not appropriate to report a single λ estimate because λ varied by density. We have chosen to report the 25th, 50th (or median), and 75th percentile estimates in all tables and the median estimates in the figures. Supporting Information Additional supporting information may be found in the online version of this article at the publisher's website. Filename Description jwmg21560-sup-0001-SuppData-S1.docx1.8 MB Supporting Data S1. jwmg21560-sup-0002-SuppData-S2.docx343.6 KB Supporting Data S2. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. LITERATURE CITED Case, T. J. 2000. An illustrated guide to theoretical ecology. Oxford University Press, New York, New York, USA. Dennis, B., P. L. Munholland, and J. M. Scott. 1991. Estimation of growth and extinction parameters for endangered species. Ecological Monographs 61: 115– 143. Dennis, B., and M. L. Taper. 1994. Density dependence in time series observations of natural populations: estimation and testing. Ecological Monographs 64: 205– 224. Jacobson, A. R., A. Provenzale, A. von Hardenberg, B. Bassano, and M. Festa-Bianchet. 2004. Climate forcing and density dependence in a mountain ungulate population. Ecology 85: 1598– 1610. Mills, L. S. 2013. Conservation of wildlife populations: demography, genetics, and management. Second edition. John Wiley & Sons, Chichester, West Sussex, United Kingdom. Morris, W. F., D. F. Doak. 2002. Quantitative conservation biology: theory, practice of population viability analysis. Sinauer, Sunderland, Massachusetts, USA. Ricker, W. E. 1954. Stock and recruitment. Journal of the Fisheries Board of Canada 11: 559– 623. Citing Literature Volume82, Issue8November 2018Pages 1808-1808 ReferencesRelatedInformation

Estimation of density and distribution functions of a Burr X distribution

Burr type X distribution is one of the members of the Burr family which was originally derived by Burr (1942) and can be used quite effectively in modelling strength data and also general lifetime data. In this article, we consider efficient estimation of the probability density function (PDF) and cumulative distribution function (CDF) of Burr X distribution. Eight different estimation methods namely maximum likelihood estimation, uniformly minimum variance unbiased estimation, least square estimation, weighted least square estimation, percentile estimation, maximum product estimation, Cremer-von-Mises estimation and Anderson-Darling estimation are considered. Analytic expressions for bias and mean squared error are derived. Monte Carlo simulations are performed to compare the performances of the proposed methods of estimation for both small and large samples. Finally, a real data set has been analyzed for illustrative purposes.

Different estimation methods for exponentiated Rayleigh distribution under constant‐stress accelerated life test

AbstractThe accelerated life testing is an efficient approach and has been used in several fields to obtain failure time data of test units in a much shorter time than testing at normal operating conditions. In this article, we consider 6 frequentist estimation methods, namely, method of maximum likelihood estimation, method of least square estimation, method of weighted least square estimation, method of percentile estimation, method of maximum product of spacing estimation, and method of Cramér‐von‐Mises estimation to estimate the parameters and the reliability function of the exponentiated Rayleigh distribution under normal use conditions using constant accelerated life testing. Monte Carlo simulations are performed to compare the performances of the proposed methods of estimation for both small and large samples. The performances of the estimators have been compared in terms of their mean squared error using simulated samples. Simulation results showed that percentile method gives the best results among other estimation methods in terms of mean squared error. Finally, a real data set is analyzed for illustrative purposes.

Inferential statistics of Quercus species in veneer cutting

Quercus species represent 18% of the total forest area in Romania, of which 2% refers to common oak and 10.5% refers to sessile oak. These species are of special importance for Romanian silviculture due to their value in multiple industrial uses. The finest and most efficient use of valuable timber is wood veneer. This paper presents a comparative analysis of the efficiency in veneer cutting for two Quercus species, common oak and sessile oak, originating from the Snagov area in Romania. The statistical parameters of veneer efficiency were estimated with high accuracy by using the least squares method with a 95% normal confidence interval based on the Anderson-Darling test and the correlation coefficient. The analysis of inferential statistics used the estimation of the 87th percentile, determining the cumulative density functions for the species under study. More defects were found in common oak logs than in sessile oak logs, which produced more veneer sheets. The veneer efficiency for sessile oak logs was superior to that of common oak logs. These findings might have practical applications in industrial conditions when screening for the best log species with high efficiency in veneer cutting.

Fetal growth velocity: the NICHD fetal growth studies

Accurately identifying pregnancies with accelerated or diminished fetal growth is challenging and generally based on cross-sectional percentile estimates of fetal weight. Longitudinal growth velocity might improve identification of abnormally grown fetuses. We sought to complement fetal size standards with fetal growth velocity, develop a model to compute fetal growth velocity percentiles for any given set of gestational week intervals, and determine association between fetal growth velocity and birthweight. This was a prospective cohort study with data collected at 12 US sites (2009 through 2013) from 1733 nonobese, low-risk pregnancies included in the singleton standard. Following a standardized sonogram at 10w0d-13w6d, each woman was randomized to 1 of 4 follow-up visit schedules with 5 additional study sonograms (targeted ranges: 16-22, 24-29, 30-33, 34-37, and 38-41 weeks). Study visits could occur ± 1 week from the targeted GA. Ultrasound biometric measurements included biparietal diameter, head circumference, abdominal circumference, and femur length, and estimated fetal weight was calculated. We used linear mixed models with cubic splines for the fixed effects and random effects to flexibly model ultrasound trajectories. We computed velocity percentiles in 2 ways: (1) difference between 2 consecutive weekly measurements (ie, weekly velocity), and (2) difference between any 2 ultrasounds at a clinically reasonable difference between 2 gestational ages (ie, velocity calculator). We compared correlation between fetal growth velocity percentiles and estimated fetal weight percentiles at 4-week intervals, with 32 (±1) weeks' gestation for illustration. Growth velocity was computed as estimated fetal growth rate (g/wk) between ultrasound at that gestational age and from prior visit [ie, for 28-32 weeks' gestational age: velocity= (estimated fetal weight 32-28)/(gestational age 32-28)]. We examined differences in birthweight by whether or not estimated fetal weight and estimated fetal weight velocity were <5th or ≥5th percentiles using χ2. Fetal growth velocity was nonmonotonic, with acceleration early in pregnancy, peaking at 13, 14, 15, and 16 weeks for biparietal diameter, head circumference, femur length, and abdominal circumference, respectively. Biparietal diameter, head circumference, and abdominal circumference had a second acceleration at 19-22, 19-21, and 27-31 weeks, respectively. Estimated fetal weight velocity peaked around 35 weeks. Fetal growth velocity varied slightly by race/ethnicity although comparisons reflected differences for parameters at various gestational ages. Estimated fetal weight velocity percentiles were not highly correlated with fetal size percentiles (Pearson r= 0.40-0.41, P < .001), suggesting that these measurements reflect different aspects of fetal growth and velocity may add additional information to a single measure of estimated fetal weight. At 32 (SD ± 1) weeks, if both estimated fetal weight velocity and size were <5th percentile, mean birthweight was 2550 g; however, even when size remained <5th percentile but velocity was ≥5th percentile, birthweight increased to 2867 g, reflecting the important contribution of higher growth velocities. For estimated fetal weight ≥5th percentile, but growth velocity <5th, birthweight was smaller (3208 vs 3357 g, respectively, P < .001). We provide fetal growth velocity data to complement our previous work on fetal growth size standards, and have developed a calculator to compute fetal growth velocity. Preliminary findings suggest that growth velocity adds additional information over knowing fetal size alone.

Efficient estimation of Pareto model: Some modified percentile estimators.

The article proposes three modified percentile estimators for parameter estimation of the Pareto distribution. These modifications are based on median, geometric mean and expectation of empirical cumulative distribution function of first-order statistic. The proposed modified estimators are compared with traditional percentile estimators through a Monte Carlo simulation for different parameter combinations with varying sample sizes. Performance of different estimators is assessed in terms of total mean square error and total relative deviation. It is determined that modified percentile estimator based on expectation of empirical cumulative distribution function of first-order statistic provides efficient and precise parameter estimates compared to other estimators considered. The simulation results were further confirmed using two real life examples where maximum likelihood and moment estimators were also considered.