Substantial Source Of Error Research Articles

Deriving biomass conversion factors for southern temperate benthic fauna; analytical methods matter

Biomass is a fundamental ecological measure used to quantify ecosystem structure and function. It is costly to measure but can be estimated using conversion factors based on established relationships between different biomass measures, however such conversion factors may not be applicable across broad geographic regions. For temperate benthic fauna, currently available mass-to-mass conversion factors were largely established in Northern Hemisphere ecosystems. Here, we present conversion factors for temperate Australian benthic fauna typically found in microtidal coastal bays and estuaries (14 taxa encompassing five classes: Polychaeta; Bivalvia; Gastropoda; Crustacea; Insecta). We derived 126 conversion factors using two statistical techniques between several mass measures (e.g. wet mass, dry mass, ash-free dry mass, shell-free masses) with specimens from three preservation methods (ethanol, formalin, frozen). Our conversion factors were generally not congruent with those obtained from the literature. We also found that the choice of prediction method used to derive conversion factors can be a substantial source of error in biomass estimation that has largely been overlooked in mass-to-mass conversion. Log-linear ordinary least squares regression models provided substantially more accurate predictions than simple mean ratios. We outline an analytical approach for future use to derive more globally comparable conversion factors for estuarine benthic fauna.

High correlation between inner and outer glenoid circle diameters and its clinical relevance.

The majority of methods for measuring glenoid bone loss in shoulder instability use the best-fit circle following the inferior glenoid rim. However, there is no precise method on how to draw this circle, particularly in case of a missing rim segment. Defining the radius is a source of substantial error. It was hypothesized that there is a relationship between the best-fit inferior circle (inner circle), defined by Sugaya, and the circle tangent to the supra- and infra-glenoid tubercles (outer circle), defined by Itoi, thus allowing a more consistent appreciation of the paleo-glenoid. Ninety-five normal dry scapulae were examined. The specimens were digitally photographed obtaining perpendicular images of the glenoid cavity. Using HOROS® imaging software, a best-fit inferior circle (inner circle) and a second circle fitting the most inferior and superior points of the glenoid (outer circle) were drawn by two investigators. The diameters and areas of the circles were recorded. Two-way random-effects intra-class correlation coefficients (ICC) were used to measure intra- and inter-observer agreement. A Bayesian measurement-error regression model was used to determine the relationship between outer and inner circle measurements. The mean glenoid height was 35.1mm and the glenoid width 25.6mm. The mean diameter of the outer circle was 35.7 ± 4.2mm and the mean diameter of the inner circle was 26.8 ± 3.2mm. ICC showed excellent inter- and intra-observer agreement for both the outer circle diameter (ICC ≥ 0.95) and inner circle diameter (ICC ≥ 0.93). The two diameters demonstrated a very strong significant Pearson correlation (0.92, p < 0.001) and the regression showed excellent model fit R2 = 0.87. The areas of the two circles were also highly and significantly correlated (r = 0.94; p < 0.001). The ratio of inner circle to outer diameters was 0.74. There is a strong correlation between the inner and outer glenoid circle diameters. This study sets the base for the use the combined outer and inner circle and its ratio to better appreciate the paleo-glenoid morphology and thus obtain a more reliable bone loss estimation. Application of this method aids in a more reliable estimation bone loss with potential benefit in surgical decision-making.

Correcting inter-scan motion artifacts in quantitative R1 mapping at 7T.

PurposeInter‐scan motion is a substantial source of error in R1 estimation methods based on multiple volumes, for example, variable flip angle (VFA), and can be expected to increase at 7T where B1 fields are more inhomogeneous. The established correction scheme does not translate to 7T since it requires a body coil reference. Here we introduce two alternatives that outperform the established method. Since they compute relative sensitivities they do not require body coil images.TheoryThe proposed methods use coil‐combined magnitude images to obtain the relative coil sensitivities. The first method efficiently computes the relative sensitivities via a simple ratio; the second by fitting a more sophisticated generative model.Methods R1 maps were computed using the VFA approach. Multiple datasets were acquired at 3T and 7T, with and without motion between the acquisition of the VFA volumes. R1 maps were constructed without correction, with the proposed corrections, and (at 3T) with the previously established correction scheme. The effect of the greater inhomogeneity in the transmit field at 7T was also explored by acquiring B1+ maps at each position.ResultsAt 3T, the proposed methods outperform the baseline method. Inter‐scan motion artifacts were also reduced at 7T. However, at 7T reproducibility only converged on that of the no motion condition if position‐specific transmit field effects were also incorporated.ConclusionThe proposed methods simplify inter‐scan motion correction of R1 maps and are applicable at both 3T and 7T, where a body coil is typically not available. The open‐source code for all methods is made publicly available.

Computational fluid dynamics analysis of char conversion in Sandia's pressurized entrained flow reactor.

Design and analysis of practical reactors utilizing solid feedstocks rely on reaction rate parameters that are typically generated in lab-scale reactors. Evaluation of the reaction rate information often relies on assumptions of uniform temperature, velocity, and species distributions in the reactor, in lieu of detailed measurements that provide local information. This assumption might be a source of substantial error, since reactor designs can impose significant inhomogeneities, leading to data misinterpretation. Spatially resolved reactor simulations help understand the key processes within the reactor and support the identification of severe variations of temperature, velocity, and species distributions. In this work, Sandia's pressurized entrained flow reactor is modeled to identify inhomogeneities in the reaction zone. Tracer particles are tracked through the reactor to estimate the residence times and burnout ratio of introduced coal char particles in gasifying environments. The results reveal a complex mixing environment for the cool gas and particles entering the reactor along the centerline and the main high-speed hot gas reactor flow. Furthermore, the computational fluid dynamics (CFD) results show that flow asymmetries are introduced through the use of a horizontal gas pre-heating section that connects to the vertical reactor tube. Computed particle temperatures and residence times in the reactor differ substantially from the idealized plug flow conditions typically evoked in interpreting experimental measurements. Furthermore, experimental measurements and CFD analysis of heat flow through porous refractory insulation suggest that for the investigated conditions (1350 °C, <20 atm), the thermal conductivity of the insulation does not increase substantially with increasing pressure.

Cognitive Schemas among Mental Health Professionals and Other Health Professionals.

Objective:Research has demonstrated that dysfunctional cognitive schemas among mental health professionals (MHPs) may influence the ability to process clients’ information in an unbiased manner, may be a substantial source of error in psychotherapeutic ratings, hinder accurate reporting of clients’ cognitive schemas, and have a detrimental effect on therapeutic alliance. The present study compared cognitive schemas among MHPs and other health professionals (OHPs).Materials and Method:A sample of 128 professionals (64 MHPs and 64 OHPs) was chosen using a purposive sampling technique. The study used a cross-sectional observational research design. The Young Schema Questionnaire Short Form 3rd version was administered on the consenting participants.Results:OHPs had higher maladaptive schemas on the domains of abandonment and defectiveness. Overall, males had more maladaptive schemas in the domains of abandonment, mistrust, entitlement/superiority, admiration/recognition seeking, and emotional inhibition. Among MHPs, a weak positive correlation of years of experience with vulnerability to harm or illness was seen. Among other health professionals, a significant but weak positive correlation of age with admiration/recognition seeking was seen.Conclusion:This study highlights the presence of maladaptive schemas in health professionals and the need for incorporation of training modules to address these.

Effects of the interstellar medium on detection of low-frequency gravitational waves

Time variable delays due to radio wave propagation in the ionized interstellar medium are a substantial source of error in pulsar timing array efforts. We describe the physical origin of these effects, discussing dispersive and scattering effects separately. Where possible, we give estimates of the magnitude of timing errors produced by these effects and their scaling with radio frequency. Although there is general understanding of the interstellar medium propagation errors to be expected with pulsar timing array observations, detailed comparison between theory and practice is still in its infancy, particularly with regard to scattering effects.

Ground reference data error and the mis-estimation of the area of land cover change as a function of its abundance

Area estimation is a common application of remote sensing especially in relation to studies of land cover change. The use of an imperfect, nongold-standard, reference is shown to be a source of substantial error in estimates of change area. The relationships between the accuracy of land cover classifications, both real and perceived, together with area of change are explored over the full range of change abundance. The magnitude of mis-estimation varies with the abundance of change and the quality of the data sets used but may be large. For scenarios based on realistic values of data set quality for the common situation in which change is rare, ≤1%, change area was overestimated by up to two orders of magnitude because of reference data error. The results highlight that the ability of remote sensing to provide accurate information on change area is limited by reference data error and is, in part, a function of change abundance.

Evaluation of the quantitative accuracy of a commercially available positron emission mammography scanner

The PEM Flex Solo II (Naviscan, Inc., San Diego, CA) is currently the only commercially available positron emission mammography (PEM) scanner. This scanner does not apply corrections for count rate effects, attenuation, or scatter during image reconstruction, potentially affecting the quantitative accuracy of images. The aim of this work is to measure the overall quantitative accuracy of the PEM Flex system and to determine the individual contributions of error from count rate effects, attenuation, and scatter. Gelatin phantoms were designed to simulate breasts of different thicknesses (4-12 cm) with varying uniform background activity concentration (AC) (0.007-0.5 microCi/cc), cysts, and lesions (2:1, 5:1, and 10:1 lesion-to-background ratios). The overall error was calculated from ROI measurements in the phantoms with a clinically relevant background AC (0.065 microCi/cc). The error due to count rate effects was determined by comparing the overall error at multiple background AC to the error at a very low background AC (0.007 microCi/cc) where count rate effects are considered negligible. A point source and cold gelatin phantoms of different thicknesses were used to assess the errors due to attenuation and scatter. The maximum pixel values of the point source in gelatin and in air were compared to determine the effect of attenuation, while scatter was evaluated by comparing the sum of all pixel values in gelatin and in air. The AC in the uniform background was underestimated in phantoms of all thicknesses, with the exception of the 4-cm-thick phantoms in which the measured AC was within +/- 7% of the true value (0.065 microCi/cc). The degree of underestimation in the uniform background increased with the phantom thickness, up to 34% +/- 6% in the 12 cm phantoms. The AC in all lesions was underestimated by more than that measured in the background (22% for the 2:1 lesions in the 4 cm phantom) and this underestimation increased with increasing thickness and lesion-to-background ratio (85% for the 10:1 lesions in the 12 cm phantoms). The error due to count rate effects reduced the measured AC with respect to its true value. This error increased with increasing background AC (23% +/- 6% at 0.065 microCi/cc to 85% +/- 1% at 0.5 microCi/cc for the 4 cm phantoms) and decreased with increasing phantom thickness (23% +/- 6% for the 4-cm-thick phantoms to 7% +/- 7% for the 12-cm-thick phantoms at 0.065 microCi/cc). Attenuation was a substantial source of error and reduced the measured AC by 51% +/- 10%-77% +/- 4% in the 4-12 cm phantoms, respectively. Scatter increased the total signal measured in images by a relatively constant amount (23% +/- 9%) for all thicknesses. Applying corrections for count rate effects, attenuation, and scatter will be essential for the PEM Flex Solo II to be able to produce quantitatively accurate images.

How do introduction characteristics influence the invasion success of Mediterranean alien plants?

Abstract Invasive plant species are becoming increasingly widespread following accelerated anthropogenic activity in the Mediterranean region. Humans have played a central role in the expansion process, and it is important to incorporate such considerations into management plans. Using generalized linear models, our first aim was to describe how the invasion success of 862 prominent alien plant species on Mediterranean islands is related to characteristics of the introduction process: introduction frequency, date and region of origin, range size and purpose of import. The importance of each was measured by the numbers of species present and their average invasiveness. The main findings were: (a) accidental imports and ornamentals accounted for a high proportion of all aliens, although neither group had particularly high average invasiveness; (b) introduction frequency had a comparatively modest influence, with the most commonly-introduced species naturalized only three times more widely than those rarely-introduced; (c) rates of species introduction appear to have increased dramatically in the last century, although aliens which have been present in the region for more than 200 years were most widespread, indicating that it may be centuries before some species fill their potential range; (d) there were small tendencies for successful invaders to originate in the Neotropics or in regions with Mediterranean climate biomes and to have large range sizes. Our second aim was to determine whether the number or average invasiveness of species introduced via a given pathway had the most influence on the overall probability of invasion on a given island. An elasticity analysis suggested that the number of species was substantially the best predictor of the two. This finding arises largely because invasion events are rare and remain unpredictable, and has significant implications for assessing invasion risk. We discuss how substantial sources of error and intrinsic variability in invasiveness within species groups limit the potential for developing accurate risk models.

Bias in psychotherapist ratings of client transference and insight.

The psychology literature at large considers rater bias to be a substantial source of error in observer ratings. Yet, it is typically ignored by psychotherapy researchers using participant (psychotherapist/client) ratings. In particular, interrater variability, or differences between raters' overall tendency to rate others favorably or unfavorably, has been a largely ignored source of error in studies that use psychotherapists and/or clients as raters. Ignoring rater bias can have serious consequences for statistical power and for interpretation of research findings. Rater bias may be a particular problem in psychotherapy research, as psychotherapists are often asked to rate subjective variables that require much rater inference. Consequently, we examined the extent to which rater bias is a factor in psychotherapist ratings of client transference and insight, by comparing psychotherapist variance from these ratings to psychotherapist variance in ratings of client-perceived emotional intelligence, using Hierarchical Linear Modeling. Results suggest that bias may be a substantial source of error in psychotherapist process and relationship ratings, accounting for, on average, 38% of the total variance in scores, and 30% after accounting for perceived emotional intelligence. (PsycINFO Database Record (c) 2010 APA, all rights reserved).

Bias in participant ratings of psychotherapy process: An initial generalizability study.

Rater bias has long been considered a source of error in observer ratings but has been ignored by process researchers using participant ratings. In particular, rater variance, or differences in generalized favorable or unfavorable perceptions of others, represents a neglected source of error in studies using participant ratings. The author presents an initial generalizability study of 2 commonly used psychotherapy process measures and discusses the implications for statistical power of studies using these measures and for interpretation of research findings. Results suggest that bias may be a substantial source of error in process ratings, accounting for 4 to 8 times as much variance in observed scores as intrarater error.

The Dependability and Interchangeability of Assessment Methods in Science

In this study, we investigated the importance of occasion as a source of error variance in (a) estimates of the dependability (generalizability) of science assessment scores and (b) the interchangeability of science test formats. Two science tests were developed to measure 8th-grade students' knowledge of concepts related to electricity and electric circuits: A hands-on assessment that provided students with equipment to manipulate and an analogous pencil-and-paper version. Students were administered both tests on 2 occasions, approximately 1 month apart. Results of the univariate generalizability results showed that explicitly recognizing occasion as a facet of error variance altered the interpretation about the substantial sources of error in the measurement and gave lower estimates of the dependability of science scores. Including occasion as an explicit source of variance in the multivariate generalizability analyses influenced the interpretation of the observed correlation between hands-on and pencil-and-paper scores but had little influence on the estimated disattenuated correlation between assessment methods.

Rater bias in psychological research: When is it a problem and what can we do about it?

Rater bias is a substantial source of error in psychological research. Bias distorts observed effect sizes beyond the expected level of attenuation due to intrarater error, and the impact of bias is not accurately estimated using conventional methods of correction for attenuation. Using a model based on multivariate generalizability theory, this article illustrates how bias affects research results. The model identifies 4 types of bias that may affect findings in research using observer ratings, including the biases traditionally termed leniency and halo errors. The impact of bias depends on which of 4 classes of rating design is used, and formulas are derived for correcting observed effect sizes for attenuation (due to bias variance) and inflation (due to bias covariance) in each of these classes. The rater bias model suggests procedures for researchers seeking to minimize adverse impact of bias on study findings.

The Generalizability of a Performance Assessment Measuring Achievement in Eight-Grade Mathematics

In this article, we examined temporal stability and intertask consistency of an 8th-grade mathematics performance assessment and investigated how task similarity affects the ability to generalize results of the assessments. Four performance tasks, 2 being highly similar, were developed to measure a complex problem-solving domain from a Midwestern state's learner outcomes. Interrater reliability coefficients averaged in the .80s; however, test-retest reliability coefficients were considerably lower, ranging from .28 to .54. Generalizability study results showed substantial sources of error due to task main effects and interactions with other facets, although these error variance components were substantially smaller when only the 2 highly similar tasks were analyzed. Analyses showed that the number of tasks required to reach acceptable levels of generalizability would be prohibitively high, even using only highly similar tasks. The findings are consistent with previous research and should encourage cautious use of performance assessment tasks such as these in high-stakes testing situations.

The Small‐Scale Velocity Dispersion of Galaxies: A Comparison of Cosmological Simulations

The velocity dispersion of galaxies on small scales (r D 1 h~1 Mpc), can be estimated from the p 12 (r), anisotropy of the galaxy-galaxy correlation function in redshift space (Davis & Peebles). We apply this technique to mock catalogs II extracted from N-body simulations of several di†erent variants of cold dark matterEdominated cosmological models, including models with cold ) hot dark matter, to obtain results that may be compared consistently with similar results from observations. We -nd a large varia- tion in the value of h~1 Mpc) in di†erent regions of the same simulation. We investigate the e†ects p 12 (1 of removing clusters from the simulations, using an automated cluster-removing routine, and -nd that this reduces the sky variance but also reduces the discrimination between models. However, studying p 12 as clusters with di†erent internal velocity dispersions are removed leads to interesting information about the amount of power on cluster and subcluster scales. We compute the pairwise velocity dispersion directly, in order to check the Davis-Peebles method, and -nd agreement of better than 20% in all the models studied. We also calculate the mean streaming velocity and the pairwise peculiar velocity dis- tribution in the simulations, and compare these with the models used in the Davis-Peebles method. We -nd that the model for the mean streaming velocity may be a substantial source of error in the calcu- lation of p 12 . Subject headings: cosmology: theory E galaxies: clusters: general E galaxies: distances and redshifts E large-scale structure of universe

Generalised approach to the recognition of structurally similar handwritten characters using multiple expert classifiers

It is observed that a particular classifier using a particular set of features will generally exhibit a greater probability of confusion among certain character classes than among others. In general these confusion classes are a substantial source of error in the overall performance of the classifier. A productive way to deal with the problem is to separate these characters and reprocess them further in an independent secondary stage in the framework of a multiple expert configuration. The philosophy is to use multiple classifiers to re-evaluate these relatively difficult characters by treating them as special and specific problem cases. In extending special treatment to these characters, advantage can be taken of distinctive structural features to design tailor-made algorithms suited to a particular problem. Since such classifiers are required to deal only with a limited number of classes, very versatile classifiers can be implemented. The main difficulty of this philosophy is to devise a way to group characters together to make sure that these specialised classifiers receive a stream of input characters which indeed belong to the particular group of characters associated with that particular classifier. The authors present a general philosophy for multi-expert classification and deal with the specific problem of formation of distinctive character streams with a high degree of confidence. It then elaborates on other techniques and variations that can be adopted to make this type of multiple expert configuration more effective.

Mortality of American Indian and Alaska native infants.

Accurate determination of infant mortality rates among Indians in seriously hampered by variations in the identification of Indian persons and use of different subsets of the Indian population for various purposes. Lack of consistency in the reporting of racial origin on birth and death records is a source of substantial error. Because of these factors, more than the usual care must attend comparisons and inferences drawn from data in which these differences are present. At present, it would seem prudent to regard all data about American Indians as provisional. Even though Indian infant mortality remains higher than that for US all races, regardless of techniques used for estimates, the decline of Indian infant mortality by more than 80% since the establishment of the IHS is a truly remarkable achievement. This success has been ascribed to a combination of activities, including the provision of safe drinking water, especially as an integral part of the IHS program; the nearly universal immunization of Indian children; and emphasis upon comprehensive, community-oriented programs focused on maternal and child care. These successes have contributed to changes in the distribution of the leading causes of Indian infant mortality, so that the most prominent causes now are SIDS, congenital anomalies, injuries, and various infections. Because of these changes and advances in knowledge, the IHS has recently revised its five-year plan for dealing with infant mortality to provide greater attention to injuries and infections and has embarked upon a series of discussions with the American Academy of Pediatrics to address postneonatal deaths and the difficult problem of SIDS. Low socioeconomic conditions, so important in influencing mortality rates (7, 14, 29), have thus far proved to be intractable. In the meantime, success will depend upon ensuring optimal prenatal care, reducing those risk factors amenable to correction, and solving the problem of SIDS.

Evaluation of Three Methods for Measurement of Femoral Neck Anteversion

A variety of methods exist for determining femoral neck anteversion. There is, however, no consistent definition or reference method by which the correctness of the measurements can be determined. In this report the precision of a specific definition of femoral neck anteversion is estimated by means of a reference method. Three different radiologic measuring methods based on fundamentally different principles are evaluated by comparison with this reference. It is concluded that: 1) The Dunlap/Rippstein method can be recommended as the standard method. 2) Computed tomography may have substantial sources of error. 3) Methods based on arbitrary projections have poor precision.

Aspects of femoral neck anteversion

Although the general definition of femoral neck anteversion seems to be accepted, the details vary substantially and some measuring methods are based on anatomic prerequisites that are lacking. This may be a cause of inconsistent and incorrect determinations. an anatomic study was therefore performed. Only small differences were found between two neck axes and different methods for delineating the axes. Inconsistent use of the shaft axis gave substantial variations. the long axis of the femoral shaft was, however, not shown to be a source of substantial error. the variation between three different knee axes was substantial. the cross section of the femoral neck was found to be radially asymmetric. Therefore, a precise and unequivocal neck centre cannot be made by any combination of bi-plane projections of the neck

Aspects of femoral neck anteversion. Theoretical considerations and experimental results.

Although the general definition of femoral neck anteversion seems to be accepted, the details vary substantially and some measuring methods are based on anatomic prerequisites that are lacking. This may be a cause of inconsistent and incorrect determinations. An anatomic study was therefore performed. Only small differences were found between two neck axes and different methods for delineating the axes. Inconsistent use of the shaft axis gave substantial variations. The long axis of the femoral shaft was, however, not shown to be a source of substantial error. The variation between three different knee axes was substantial. The cross section of the femoral neck was found to be radially asymmetric. Therefore, a precise and unequivocal neck centre cannot be made by any combination of bi-plane projections of the neck.