Subgroup Size Research Articles

A decision-making support system module for project manager selection according to past performance

This paper proposes a decision-making support system (DMSS) module for selecting project managers and demonstrates its implementation. The selection of a new project manager is based mainly on the past performance of potential managers, for example, on the relative performance evaluations they have received on projects managed by them in the past. Past projects are ranked in accordance with a ranking method. Project managers are ordered according to past project rank. The difference in quality between the past performance of the candidates is statistically examined using the Mann–Whitney–Wilcoxon U test. This enables the establishment of a subgroup of one or more preferred candidates, where the significance level of the statistical test has an impact on the subgroup size. The final candidate may be selected from this subgroup according to personal qualifications and suitability for the specific project. We demonstrated the use of such a DMSS module by an Israeli information technology company as part of their process to select a project manager. A ranking method within the Data Envelopment Analysis context (the Cross-Efficient method) was implemented with three inputs and four outputs selected for the project ranking.

Neuropsychiatric Lupus: The Prevalence and Autoantibody Associations Depend on the Definition: Results from the 1000 Faces of Lupus Cohort

The (ever) prevalence of neuropsychiatric systemic lupus erythematosus (NPSLE) can vary widely depending on the definition used. We determined the prevalence of NPSLE in 1000 Faces of Lupus, a large multicenter Canadian cohort. Adults enrolled at 10 sites who satisfied the American College of Rheumatology (ACR) classification for systemic lupus erythematosus (SLE) were included. NPSLE was defined as (i) NPSLE by ACR classification criteria (seizures or psychosis), (ii) ACR, SLEDAI (seizure, psychosis, organic brain syndrome, cranial nerve disorder, headache, and cerebrovascular accident (CVA)), SLAM (CVA, seizure, cortical dysfunction, and headache), and SLICC (cognitive impairment, psychosis, seizures, CVA, cranial or peripheral neuropathy, and transverse myelitis) with and (iii) without minor nonspecific NPSLE manifestations (including mild depression, mild cognitive impairment, and electromyogram-negative neuropathies), and (iv) by ACR and SLEDAI neuropsychiatric (NP) indexes alone. Factors associated with NPSLE were explored using regression models. Cohort size was 1253, with mean disease 12 ± 10 years, mean age 41 ± 16 years, and 86% female. Subgroup size was dependent on the specific definition of NPSLE. Prevalence of NPSLE was 6.4% in group (i), n = 1253 (n = 80); 38.6% in group (ii), n = 681(n = 263); 28.7% in group (iii), n = 586 (n = 168); and 10.2% in group (iv), n = 1125 (n = 115). In univariate analysis, Aboriginals had a nearly 2-fold increase in frequency of NPSLE in all groups. Education level and income were not associated with NPSLE (P = 0.32 and 0.03, respectively). As well, number of ACR criteria, SLAM, age at diagnosis, disease duration, and gender were not associated with NPSLE. Anti-Ro was significantly associated in groups (i) and (iv) and antiphospholipid antibodies (aPL) were increased in groups (i), (ii), and (iii); however, this lost significance when thromboembolic events were excluded from SLICC, SLEDAI, and SLAM indexes. In group (iv), absence of anti-Sm was significant. In multivariate analysis, anti-Ro and aPL (i) and anti-Ro+ and lack of anti-Sm (iv) were significant. NPSLE was not increased in those with +anti-DNA, La, or ribonucleoprotein (RNP), lupus anticoagulant (LAC), or anticardiolipin (aCL) antibody. The prevalence and factors associated with NPSLE varied depending on the definition used, was highest in Aboriginals, and may be higher if +anti-Ro or aPL are present. SLAM and SLICC include mild subjective disease manifestations, which contributed to a 10% higher prevalence of NPSLE compared to a more strict definition. NPSLE may be less in this database than other publications as its overall prevalence may be decreasing, or because of selection bias inherent to those who enter an observational cohort. NPSLE was associated with aPL and often anti-Ro and varied by ethnicity.

P4-09-27: Can We Predict the Benefit of the 70-Gene Signature in the Choice of Adjuvant Systemic Treatment for ER Positive, HER2 Negative Tumors in Daily Practice? A Single Institution Experience.

Abstract Purpose: Studies have shown that the 70-gene signature (MammaPrint®) (MP) may outperform clinicopathological risk assessment and may predict the benefit from chemotherapy (CT) in patients (pts) with early-stage breast cancer. However, the need of fresh tissue and the high cost of the assay limit its use in daily clinical practice. We investigated whether 1) tumor clinicopathologic features can predict MP risk (high vs. low); 2) MP results could help to make decisions for the use of CT in pts with ER positive (ER+ve) breast cancer beyond recommendations of known international guidelines (NCCN, St. Gallen). Patients and methods: Women with operable invasive breast cancer without evidence of distant disease undergoing surgery at the Breast Surgery Department were enrolled into the study. A 3 mm punch biopsy of the tumor was obtained from the specimen within the first hour after surgery. Samples were shipped to the laboratory in an RNA-stabilizing solution and were studied to ensure the presence of at least 30% of tumor cells and a customized microarray containing 70 genes was analyzed as described by the manufacturer. Results: 124 consecutive pts were enrolled into the study; 106 tumor samples were adequate for the microarray. Median age was 53 yrs (range 28–83), mean tumor size was 2.3 cm (SD ±1.34), 52.4% pts had pN0, 55% of tumors had Ki-67 ≥20% and 36% were poorly differentiated. ER were detected in ≥50% of cells in 82% and <1% of cells in 15% of tumors, respectively; HER2 was positive in 18% of tumors. As expected, poorly differentiated, ER and PgR negative, HER2 positive and highly proliferating tumors were more likely to be classified as high-MP. We then focused our analysis on ER and PgR +ve, HER2 negative tumors and assessed features correlated with MP results in this subgroup. Unexpectedly, 31/80 (39%) of these tumors were classified as high-MP vs. 49 (61%) low-MP. We found that tumor size (T1 vs. T2-T4), poor differentiation (G3 vs G1-2) and high proliferation (Ki-67 ≥20%) were significantly associated with a high-MP result. In an exploratory multivariate analysis tumor size and Ki-67 remained as independent predictors of high-MP result. At last, when we compared MP risk with recommendations for AT from international guidelines we found that in the subgroup of candidates for endocrine therapy (ET) in whom the benefit from the addition of CT is undetermined, 25/68 pts (37%) were high-MP and 43 pts (63%) low-MP. When we considered recommendations for AT proposed by our multidisciplinary team according to international guidelines, 11/25 pts (44%) with high-MP received ET only and 14 pts (56%) CT + ET, while among 43 pts with low-MP only 9 received both CT and ET. Conclusions: Our study shows that the 70-gene signature was feasible in the clinical setting, as 85% of tumor samples were adequate. A substantial proportion of ER/PgR+ve, HER2 negative tumors was classified as high-MP; within this subgroup, proliferation and tumor size independently predicted high-MP results. In 20 pts, MP risk would have resulted in discordant recommendations for AT compared to those based on standard clinicopathologic features. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-09-27.

Applying propensity scores estimated in a full cohort to adjust for confounding in subgroup analyses

BACKGROUND: A correctly specified propensity score (PS) estimated in a cohort ("cohort PS") should, in expectation, remain valid in a subgroup population. OBJECTIVE: We sought to determine whether using a cohort PS can be validly applied to subgroup analyses and, thus, add efficiency to studies with many subgroups or restricted data. METHODS: In each of three cohort studies, we estimated a cohort PS, defined five subgroups, and then estimated subgroup-specific PSs. We compared difference in treatment effect estimates for subgroup analyses adjusted by cohort PSs versus subgroup-specific PSs. Then, over 10 million times, we simulated a population with known characteristics of confounding, subgroup size, treatment interactions, and treatment effect and again assessed difference in point estimates. RESULTS: We observed that point estimates in most subgroups were substantially similar with the two methods of adjustment. In simulations, the effect estimates differed by a median of 3.4% (interquartile (IQ) range 1.3-10.0%). The IQ range exceeded 10% only in cases where the subgroup had < 1000 patients or few outcome events. CONCLUSIONS: Our empirical and simulation results indicated that using a cohort PS in subgroup analyses was a feasible approach, particularly in larger subgroups. Copyright © 2011 John Wiley & Sons, Ltd.

A polarization-cohesion perspective on cross-country convergence

Understanding whether the gap between rich and poor country wellbeing is narrowing is really about whether rich and poor groups can be identified in the overall size distribution of the characteristic of interest, and how those respective subgroup size distributions are changing. Here two simple statistics for analyzing the issue are introduced which are capable of discerning, in many dimensions, changes in the underlying distributions which reflect combinations of increasing (decreasing) subgroup location differences and decreasing (increasing) subgroup spreads, which are the characteristics of polarization (de-polarization). When applied in an examination of the distribution of lifetime GDP per capita over time, the population weighted version exhibits de-polarization and the unweighted version exhibits polarization. As a collection of countries, Africa is diverging from the rest of the world regardless of the weighting scheme.

ZIB-EWMA CONTROL CHART FOR MONITORING RARE HEALTH EVENTS

Monitoring rare health events, as a significant public health subject, has been considered recently by different authors. In this regard, different statistical methods such as g-type control chart, Poisson CUSUM control chart, sets-based methods, and Bernoulli CUSUM chart have been developed. Zero-inflated binomial (ZIB) distribution, due to its structure, can also be considered to develop methods for monitoring rare health-related events. If zero inflation is considered in the sampling data, and the sampling subgroup size is mandatory greater than 1, then the data best fits the ZIB distribution and the aforementioned control charts cannot be applied. ZIB distribution assumes that random shocks, corresponding to rare health events, occur and then number of failures in each subgroup fits a binomial distribution. In this paper, an exponentially weighted moving average (EWMA) control chart is applied for ZIB data to develop a ZIB-EWMA chart. Since ZIB-EWMA statistic values are not independent, Markov chain approach is considered to evaluate the performance of the proposed control chart in terms of average run length (ARL). According to the ARL measure, this ZIB-EWMA chart has a better performance in comparison with the methods available in the literature. In addition, a real case study related to rare infections in a hospital is investigated to show the applicability of the proposed control chart.

Are More Stringent NCLB State Accountability Systems Associated With Better Student Outcomes? An Analysis of NAEP Results Across States

This study developed a comprehensive measure of the stringency level of NCLB states’ accountability systems, including the strength of their annual measurable objectives, confidence intervals, performance indexing, retesting, minimum subgroup size, and the difficulty levels of proficiency standards. This study related accountability stringency in 2003 to student achievement and achievement gaps on NAEP math and reading tests from 2003 and 2005. The results were inconsistent across grades, subjects, and ethnic groups. An increase in accountability stringency, such as requiring faster progress, not allowing for retesting, and allowing a smaller minimum subgroup size were related to improved math achievement for fourth-grade Hispanic students. Not using confidence intervals was related to higher math and reading achievement for White and Hispanic students. However, accountability stringency did not have any positive effects and even negative effects on eighth-grade Black students.

Spider monkeys

Spider monkeys

Nonparametric CUSUM and EWMA Control Charts for Detecting Mean Shifts

Nonparametric control charts are useful when the underlying process distribution is not likely to be normal or is unknown. In this paper, we propose two nonparametric analogs of the CUSUM and EWMA control charts based on the Wilcoxon rank-sum test for detecting process mean shifts. We first derive the run-length distributions of the proposed control charts and then compare the performance of the proposed nonparametric charts to (1) CUSUM and EWMA control charts on subgroup means and (2) the median chart and the Shewhart-type nonparametric control chart based on Mann–Whitney test. We show that the charts proposed herein perform well in detecting step mean shifts and perform almost the same as the parametric counterparts when the underlying process output follows a normal distribution and better when the output is nonnormal. We also study the effect of the reference sample size and the subgroup size on the performance of the proposed charts. A numerical example is also given as an illustration of the design and implementation of the proposed charts.

Quality Control Of High-Dose-Rate Brachytherapy: Treatment Delivery Analysis Using Statistical Process Control

Purpose: Statistical process control (SPC) is a quality control method used to ensure that a process is on-target and operating with minimal variation. The focus of this study is to determine if SPC is a viable technique for evaluating the proper operation of a high-dose-rate (HDR) brachytherapy treatment delivery system. Materials and Methods: Thomson-Nielsen MOSFET Dosimetry System (MOSFET model 502RD) was used as the dosimeter. MOSFET dosimeters (MD) were calibrated against a Farmer-type ionization chamber at a distance of 1.6 cm from 192Ir in water. A surrogate prostate patient was developed utilizing Vyse Ordance™ gelatin. Needle placement was performed according to our prostate HDR clinical protocol. A total of 10 MD were placed from prostate base to apex. Three detector trains of three MD each, spaced 2.5 cm apart, were inserted into two detector holders at the prostate periphery as well as in the urethra. The remaining MD was placed at the apex on the periphery. CT guidance was used to accurately position the first detector in each train at the base. The plan consisted of 12 needles with 129 dwell positions spaced 0.5 cm apart, delivering a prescribed peripheral dose of 200 cGy. Marks were placed on the needles at the template, and the distance from the template to the needle hub was recorded to allow accurate repositioning of each needle. Sixteen accurate treatment trials were delivered as planned. Subsequently a number of treatments were delivered with errors introduced. The errors were: wrong patient (i.e., a clinical plan for a different patient with 12 needles), wrong source calibration (3 & 7 day source decay inaccuracy), wrong sequence (i.e. two needles connected to incorrect location in turret), single needle displaced inferiorly 5mm, and entire implant displaced 2mm and 4mm inferiorly. Each MD constituted an evaluation subgroup size of one (bias correction factors d2 & d3 determined for n = 2 for consistency with established SPC methodology). The range was therefore determined by the difference between sequential treatment delivery measurements. Two process behavior charts (PBC), an average and range chart, were developed for each MD. Results: There were 4 false positives resulting from 160 measurements from 16 accurately delivered treatments. Generally speaking, data points resulting from accurately delivered treatments were well within PBC limits. The PBC indicate that measurements made at the base and apex were much more sensitive to treatment delivery errors. Each of the errors introduced was correctly identified by either the average or range PBC for measurements made at the base (2 out of 3 locations) and apex (all 4 locations). The PBC for measurements made at mid-gland (3 locations) were less sensitive to errors in treatment delivery. The only errors detected at these locations were “wrong patient” and “wrong source calibration.” Conclusions: SPC is a viable methodology to assess the quality of HDR treatment delivery. Further development is necessary to determine the most effective positioning of the MD for detecting potential treatment delivery errors.

Assessment of the variability in the anatomical position and size of the subthalamic nucleus among patients with advanced Parkinson’s disease using magnetic resonance imaging

Targeting of the subthalamic nucleus (STN) during deep brain stimulation (DBS) surgery using standard atlas coordinates is used in some centers. Such coordinates are accurate for only a subgroup of patients, and subgroup size depends on the extent of inter-individual variation in STN position/size and degree to which atlas represents average anatomical relations. Few studies have addressed this issue. Sixty-two axial T(2)-weighted magnetic resonance (MR) images of the brain (1.5 T) were obtained before STN-DBS in 62 patients (37 males) with Parkinson's disease using a protocol optimized for STN visualization. Image distortion was within sub-millimeter range. Midcommissural point (MCP)-derived coordinates of STN borders, STN center, and other brain landmarks were obtained using stereotactic software. MR-derived measurements were compared to Schaltenbrand and Wahren Atlas. We evaluated 117 best-visualized STNs. STN dimensions and coordinates of its center were highly variable. STN lateral coordinate ranged 8.7 mm-14.5 mm from MCP, A-P coordinate 3.5 mm posterior to 0.5 mm anterior to MCP, and vertical coordinate 1.3 mm-6 mm below MCP. The antero-posterior nucleus dimension varied by 8 mm and lateral-medial dimension by 5.8 mm. Differences between mean values of MR-derived data sets and Atlas values were statistically significant but moderate, excluding AC-PC length, for which the Atlas value was below the 1st percentile of the MR data set. The STN lateral coordinate strongly correlated with the width of the third ventricle (r = 0.73, p < 0.001). It is now possible to directly evaluate STNs at 1.5 T with minimal image distortion, which reveals variation in STN position and dimensions in the range of nucleus size. This puts under question the rationale of use of standard STN coordinates during DBS surgery.

사례수 차이가 검사동등화의 집단불변성 원칙 검증에 미치는 영향

사례수 차이가 검사동등화의 집단불변성 원칙 검증에 미치는 영향

Monitoring Variation in a Multivariate Process When the Dimension is Large Relative to the Sample Size

A control procedure is presented for monitoring changes in variation for a multivariate normal process in a Phase II operation where the subgroup size, m, is less than p, the number of variates. The methodology is based on a form of Wilk' statistic, which can be expressed as a function of the ratio of the determinants of two separate estimates of the covariance matrix. One estimate is based on the historical data set from Phase I and the other is based on an augmented data set including new data obtained in Phase II. The proposed statistic is shown to be distributed as the product of independent beta distributions that can be approximated using either a chi-square or F-distribution. An ARL study of the statistic is presented for a range of conditions for the population covariance matrix. Cases are considered where a p-variate process is being monitored using a sample of m observations per subgroup and m < p. Data from an industrial multivariate process is used to illustrate the proposed technique.

Fissioning minimizes ranging costs in spider monkeys: a multiple-level approach

The adjustment to deal with intragroup food competition is probably the most plausible explanation of high levels of fission–fusion dynamics. However, studies did not always support expected relations between food availability, ranging costs, and subgroup size. We used several levels of analysis differing in the time and spatial scale in order to investigate this explanation in spider monkeys. In our study, subgroups were larger when food availability was higher across most levels of analyses used. We also found a fine-scale adjustment: compared to the food patch previously visited, spider monkeys traveled to larger patches just after fusions. This was not without an immediate travel cost: the interpatch distance and travel time after a fusion were longer than that before the fusion. This rapid adjustment shows the flexibility that fission–fusion dynamics can offer. Spider monkeys are in large subgroups only when food conditions are favorable, as evidenced by the fact that at all the other time-scale levels larger subgroups did not experience greater ranging costs than smaller subgroups. Our results indicate that on the whole spider monkeys successfully minimize ranging costs by fission and fusion of subgroups.

High-speed wear lifetime analysis of instrument ball bearings

The instrument ball bearings often operate with high speed and light load. The common failure mode is wear-out occurring under insufficient lubrication condition. As a result, the vibration/noise and frictional torque will be enlarged, and the bearings lose accuracy and precision. In this article, the wear lifetime model of instrument ball bearings is established based on Archard's theory. A new wear coefficient curve is developed from the relationship of Archard wear coefficients obtained by a ball-plate experiment, which is related to oil type and load, with a certain lubricant film parameter (Λ). Then a computer program has been developed to calculate the location of pure rolling lines on the contact ellipse and obtain the contact stress and sliding speed on both inner and outer ball-raceway contact zones. Hence, the total wear time can be determined by the volume of wear with the allowable radial clearances. A 4000-h censored test of eight group samples, with its subgroup size of two bearings, has been conducted in special high-speed test rigs. The data of the experimental results were statistically analysed and compared with the model of wear lifetime. A consistent trend was found out between the experimental data and the proposed model.

The Influence of Feeding Patch Size and Relative Fruit Density on the Foraging Behavior of the Black Spider Monkey Ateles chamek

ABSTRACTBlack spider monkey Ateles chamek foraging data from eastern Bolivia are examined in relation to the size of fruit patches and the relative fruit density within the patch. In general, spider monkeys exhibited a preference for larger fruit patches and foraged for longer and in larger subgroups as patch size and relative fruit density increased. Nevertheless, results for specific resources revealed considerable variation in the primary variables influencing foraging behavior and subgroup size with certain specific resources more influenced by patch size, and others more influenced by relative fruit density. The results are discussed in relation to the foraging ecology of fission–fusion primate social systems and previous studies on the influence of patch size on primate foraging decisions.

Social and ecological determinants of fission–fusion dynamics in the spotted hyaena

Theory predicts that individuals living in fission–fusion societies, in which group members frequently change subgroups, should modify grouping patterns in response to varying social and environmental conditions. Spotted hyaenas, Crocuta crocuta , are long-lived carnivores that reside in permanent social groups called clans. Clans are complex, fission–fusion societies in which individual members travel, rest and forage in subgroups that frequently change composition. We studied two clans in Kenya to provide the first detailed description of fission–fusion dynamics in this species. Because social and ecological circumstances can influence the cohesiveness of animal societies, we evaluated the extent to which specific circumstances promote the formation of subgroups of various sizes. We found that cooperative defence of shared resources during interclan competition and protection from lions were cohesive forces that promoted formation of large subgroups. We also tested hypotheses suggesting factors limiting subgroup size. Mothers with small cubs avoided conspecifics, thereby reducing infanticide risk. Victims of aggression either reconciled fights or separated from former opponents to reduce the immediate costs of escalated aggression in the absence of food. As predicted by the ecological constraints hypothesis, hyaenas adjusted their grouping patterns over both short and long time scales in response to feeding competition. Crocuta were most gregarious during periods of abundant prey, joined clanmates at ephemeral kills in numbers that correlated with the energetic value of the prey and gained the most energy when foraging alone because cooperative hunting attracted numerous competitors. Overall, our findings indicate that resource limitation constrains grouping in this species.

Survey and Conservation of a Relict Population of Spider Monkeys (Ateles Geoffroyi) in the Sumidero Canyon, Mexico

Habitat loss, hunting and the pet trade have caused significant reductions in the original distribution of spider monkeys ( Ateles spp.) in the Neotropics. Mexico harbors the northernmost distribution of this primate in the Neotropics, and information on the current location of remnant populations and on their demographic features in particularly scarce. In this paper we report the results of a month-long survey during the dry season of a population of spider monkeys ( Ateles geoffroyi vellerosus) existing in the rainforest vegetation of the Sumidero Canyon National Park in central Chiapas, Mexico. The 23km-long canyon was divided into five 5km-long segments and the rainforest vegetation at the edges of the river canyon was surveyed from a boat and on the ground for presence of spider monkeys. Surveys resulted in the detection of nine subgroups of spider monkeys in four of the 5km-long segments, for an estimated total population of 36 individuals. Average subgroup size ranged from 3−7 individuals, 28% of these were adult males, 36% were adult females, 28% were juveniles and 8% were infants. Relative abundance was estimated at 1.8 monkeys/km of river. The rainforest vegetation along the river canyon has a patchy distribution and patches are separated by the steep and very tall walls of the canyon. Spider monkeys were observed to move from patch to patch by climbing the walls of the canyon. This unusual behavior allows individual spider monkeys to secure food resources and to meet other conspecifics. Additional surveys are necessary to map annual fluctuations in the size and distribution of the spider monkey population in the canyon.

A New Unified Theory of Sociobehavioural Forces

This article proposes a new unified theory of sociobehavioural forces. The goal of the new theory is to integrate theories describing five sociobehavioural processe-scomparison (including justice and self-esteem), status, power, identity, and happiness-bringing under a single theoretical umbrella diverse mechanisms together with their effects across disparate domains and for both individuals and societies. The integration is made possible by the remarkable similarity of the internal core of the theories, a core comprised of three elements: personal quantitative characteristics, personal qualitative characteristics, and primordial sociobehavioural outcomes. The unified theory posits the operation of three sociobehavioural forces-comparison, status, and power-each associated with a distinctive mechanism, in particular, a distinctive rate of change of the outcome with respect to the quantitative characteristic. Each combination of elements-e.g. status-wealth-city-generates a distinctive identity and a distinctive magnitude of happiness. Thus, the theory enables systematic and parsimonious analysis of both individuals and societies via the distinctive configurations of elements. To illustrate the unified theory, we analyse the three-way contest between loyalty to self, subgroup, and group in a two-subgroup society, deriving many new testable predictions, for example, that the bottom subgroup will have difficulty mobilizing itself; that the ablest individuals in a society will not make good leaders as their first loyalty is to self; and that the proportions loyal to self, subgroup, and group differ sharply, depending on the sociobehavioural forces, valued goods, and subgroup size. Finally, the theory provides a foundation for making explicit connections among the most important themes and insights of contemporary social science, including inequality, oppositional culture, group boundary permeability, social inclusion and exclusion, segregation and integration, social distance and polarization, and bonding and bridging.

Effectiveness of Weighted Majority Rules with Random Decision Power Distribution

AbstractThere is a large body of research studying the conditions under which majority decisions are best. In particular, in many circumstances, the probability of a group to decide correctly is higher than that of a random subgroup. Moreover, the latter probability increases as the subgroup size grows. Here we generalize those results by showing that, in the same setup, the simple majority rule is the most effective of all weighted majority rules when weights are distributed randomly between group members. For special families of weighted majority rules, rule effectiveness increases as we get “closer” to the simple majority rule.