Hypothetical Error Research Articles

Disclosing Harmful Mammography Errors to Patients

To assess radiologists' attitudes about disclosing errors to patients by using a survey with a vignette involving an error interpreting a patient's mammogram, leading to a delayed cancer diagnosis. We conducted an institutional review board-approved survey of 364 radiologists at seven geographically distinct Breast Cancer Surveillance Consortium sites that interpreted mammograms from 2005 to 2006. Radiologists received a vignette in which comparison screening mammograms were placed in the wrong order, leading a radiologist to conclude calcifications were decreasing in number when they were actually increasing, delaying a cancer diagnosis. Radiologists were asked (a) how likely they would be to disclose this error, (b) what information they would share, and (c) their malpractice attitudes and experiences. Two hundred forty-three (67%) of 364 radiologists responded to the disclosure vignette questions. Radiologists' responses to whether they would disclose the error included "definitely not" (9%), "only if asked by the patient" (51%), "probably" (26%), and "definitely" (14%). Regarding information they would disclose, 24% would "not say anything further to the patient," 31% would tell the patient that "the calcifications are larger and are now suspicious for cancer," 30% would state "the calcifications may have increased on your last mammogram, but their appearance was not as worrisome as it is now," and 15% would tell the patient "an error occurred during the interpretation of your last mammogram, and the calcifications had actually increased in number, not decreased." Radiologists' malpractice experiences were not consistently associated with their disclosure responses. Many radiologists report reluctance to disclose a hypothetical mammography error that delayed a cancer diagnosis. Strategies should be developed to increase radiologists' comfort communicating with patients.

Reporting Medical Errors to Improve Patient Safety<subtitle>A Survey of Physicians in Teaching Hospitals</subtitle>

Collecting data on medical errors is essential for improving patient safety, but factors affecting error reporting by physicians are poorly understood. Survey of faculty and resident physicians in the midwest, mid-Atlantic, and northeast regions of the United States to investigate reporting of actual errors, likelihood of reporting hypothetical errors, attitudes toward reporting errors, and demographic factors. Responses were received from 338 participants (response rate, 74.0%). Most respondents agreed that reporting errors improves the quality of care for future patients (84.3%) and would likely report a hypothetical error resulting in minor (73%) or major (92%) harm to a patient. However, only 17.8% of respondents had reported an actual minor error (resulting in prolonged treatment or discomfort), and only 3.8% had reported an actual major error (resulting in disability or death). Moreover, 16.9% acknowledged not reporting an actual minor error, and 3.8% acknowledged not reporting an actual major error. Only 54.8% of respondents knew how to report errors, and only 39.5% knew what kind of errors to report. Multivariate analyses of answers to hypothetical vignettes showed that willingness to report was positively associated with believing that reporting improves the quality of care, knowing how to report errors, believing in forgiveness, and being a faculty physician (vs a resident). Most faculty and resident physicians are inclined to report harm-causing hypothetical errors, but only a minority have actually reported an error.

Impact of correlated observation errors on inverted CO2 surface fluxes from OCO measurements

Proper assignment of error statistics is essential in the field of Bayesian inference. This paper studies the impact of correlated observation errors in the case of the estimation of CO2 surface fluxes from NASA's forthcoming Orbiting Carbon Observatory (OCO). Using a series of observation simulation system experiments, it is shown that hypothetical observation error correlations of 0.5 in neighbouring observations have a rather limited impact on the accuracy of the inverted fluxes when they are correctly taken into account. The information loss induced by commonly‐used approximate treatments of the observation error correlations (neglecting, observation thinning and error inflating), that are computationally more efficient, is quantified. Error inflation has the least detrimental impact among the suboptimal set‐ups and limits the loss in uncertainty reduction to a few per cent, in spite of its very low reduced chi‐squared.

Disclosing Medical Errors to Patients: Attitudes and Practices of Physicians and Trainees

Disclosing errors to patients is an important part of patient care, but the prevalence of disclosure, and factors affecting it, are poorly understood. To survey physicians and trainees about their practices and attitudes regarding error disclosure to patients. Survey of faculty physicians, resident physicians, and medical students in Midwest, Mid-Atlantic, and Northeast regions of the United States. Actual error disclosure; hypothetical error disclosure; attitudes toward disclosure; demographic factors. Responses were received from 538 participants (response rate = 77%). Almost all faculty and residents responded that they would disclose a hypothetical error resulting in minor (97%) or major (93%) harm to a patient. However, only 41% of faculty and residents had disclosed an actual minor error (resulting in prolonged treatment or discomfort), and only 5% had disclosed an actual major error (resulting in disability or death). Moreover, 19% acknowledged not disclosing an actual minor error and 4% acknowledged not disclosing an actual major error. Experience with malpractice litigation was not associated with less actual or hypothetical error disclosure. Faculty were more likely than residents and students to disclose a hypothetical error and less concerned about possible negative consequences of disclosure. Several attitudes were associated with greater likelihood of hypothetical disclosure, including the belief that disclosure is right even if it comes at a significant personal cost. There appears to be a gap between physicians' attitudes and practices regarding error disclosure. Willingness to disclose errors was associated with higher training level and a variety of patient-centered attitudes, and it was not lessened by previous exposure to malpractice litigation.

Modeling the euglycemic hyperinsulinemic clamp by stochastic differential equations

The Euglycemic Hyperinsulinemic Clamp (EHC) is the most widely used experimental procedure for the determination of insulin sensitivity. In the present study, 16 subjects with BMI between 18.5 and 63.6 kg/m(2) have been studied with a long-duration (5 hours) EHC. In order to explain the oscillations of glycemia occurring in response to the hyperinsulinization and to the continuous glucose infusion at varying speeds, we first hypothesized a system of ordinary differential equations (ODEs), with limited success. We then extended the model and represented the experiment using a system of stochastic differential equations (SDEs). The latter allow for distinction between (i) random variation imputable to observation error and (ii) system noise (intrinsic variability of the metabolic system), due to a variety of influences which change over time. The stochastic model of the EHC was fitted to data and the system noise was estimated by means of a (simulated) maximum likelihood procedure, for a series of different hypothetical measurement error values. We showed that, for the whole range of reasonable measurement error values: (i) the system noise estimates are non-negligible; and (ii) these estimates are robust to changes in the likely value of the measurement error. Explicit expression of system noise is physiologically relevant in this case, since glucose uptake rate is known to be affected by a host of additive influences, usually neglected when modeling metabolism. While in some of the studied subjects system noise appeared to only marginally affect the dynamics, in others the system appeared to be driven more by the erratic oscillations in tissue glucose transport rather than by the overall glucose-insulin control system. It is possible that the quantitative relevance of the unexpressed effects (system noise) should be considered in other physiological situations, represented so far only with deterministic models.

The Gap Between Nurses and Residents in a Community Hospital’s Error-Reporting System

Little is known about current attitudes and practices among residents and nurses regarding error reporting. A survey was conducted to suggest differing needs for training and other interventions to enhance reporting. The authors surveyed 24 residents and 60 nursing staff in all inpatient care units at a community hospital from 2001 to 2002. The authors used self-administered questionnaires to assess respondents' knowledge and use of the hospital's error-reporting system, perceptions and attitudes toward error reporting, reported behaviors in hypothetical error scenarios, and conditions that influence error reporting. Only half of the residents (54%) knew about the hospital's error-reporting system, whereas nearly all nurses did (97%; p = .001). Only 13% of the residents (versus 72% of the nurses) had ever used the reporting system (p = .001). Residents (29%) were less likely than nurses (64%) to report being comfortable discussing mistakes with supervisors (p = .006), and residents (38%) were more likely than nurses (0%) to rate the hospital atmosphere as nonsupportive of error reporting (p = 001). Error-reporting systems may give a biased picture of the true pattern of medical errors, and hospitals may need to initiate other interventions to improve residents' error reporting.

Localization of cerebral arterovenous malformations using digital angiography.

Since 1989 we performed stereotactic radiotherapy treatments of cerebral arterovenous malformations (AVM), estimating three-dimensional (3-D) localization and shape of target volumes by the Leksell stereotactic helmet on two orthogonal radiographic projections. Due to the limitations of this method, we developed a new technique for the localization of the target volume using digital subtraction angiography (DSA) and digital image processing. To achieve this result we first developed a method to correct nonlinear distortion of DSA images using spatial relocation of image pixels based on a calibration grid. We then developed an algorithm for localization of the target volume using two independent DSA projections. Target volume coordinates in the helmet system are calculated using two DSA acquisitions taken with a free angle (approximately 90 degrees), one in the AP and the other in the LL direction. The helmet can be freely positioned between the x-ray source and the image plane. The projections of eight reference points inserted in the helmet at a known location, are used to calculate the transformation matrix between the two coordinate systems. We performed numerical and experimental validation of the system. A hypothetical random error (up to 2 mm) on image coordinates of the reference points allowed to determine that the error in target localization was less than 0.2 mm. Using DSA images of target points with a known location within a phantom, the error between calculated and actual location was, on average, 0.30+/-0.13 mm (mean+/-SD), with a maximum error of 0.49 mm. The results of numerical and experimental validations show that the system we have developed allows fast and accurate localization of the center of the target volume and it is suitable for efficient guiding during stereotactic radiosurgery of AVM.

A neural network study of precollicular saccadic averaging.

Saccadic averaging is the phenomenon that two simultaneously presented retinal inputs result in a saccade with an endpoint located on an intermediate position between the two stimuli. Recordings from neurons in the deeper layers of the superior colliculus have revealed neural correlates of saccade averaging, indicating that it takes place at this level or upstream. Recently, we proposed a neural network for internal feedback in saccades. This neural network model is different from other models in that it suggests the possibility that averaging takes place in a stage upstream of the colliculus. The network consists of output units representing the neural map of the deeper layers of the superior colliculus and hidden layers imitating areas in the posterior parietal cortex. The deeper layers of the superior colliculus represent the motor error of a desired saccade, e.g. an eye movement to a visual target. In this article we show that averaging is an emergent property of the proposed network. When two retinal targets with different intensities are simultaneously presented to the network, the activity in the output layer represents a single motor error with a weighted average value. Our goal is to understand the mechanism of weighted averaging in this neural network. It appears that averaging in the model is caused by the linear dependence of the net input, received by the hidden units, on retinal error, independent of its retinal coding format. For nonnormalized retinal error inputs, also the nonlinearity between the net input and the activity of the hidden units plays a role in the averaging process. The averaging properties of the model are in agreement with physiological experiments if the hypothetical retinal error input map is normalized. The neural network predicts that if this normalization is overruled by electrical stimulation, averaging still takes place. However, in this case--as a consequence of the feedback task--the location of the resulting saccade depends on the initial eye position and the total intensity/current applied at the two locations. This could be a way to verify the neural network model. If the assumptions for the model are valid, a physiological implication of this paper is that averaging of saccades takes place upstream of the superior colliculus.

An Interpretation of Radiosonde Errors in the Atmospheric Boundary Layer

Abstract The authors review sources of error in radiosonde measurements in the atmospheric boundary layer and analyze errors of two radiosonde models manufactured by Atmospheric Instrumentation Research, Inc. The authors focus on temperature and humidity lag errors and wind errors. Errors in measurement of azimuth and elevation angles and pressure over short time intervals and at higher attitudes introduce wind vector errors greater than 5 m s−1. Mean temperature and humidity lag errors were small, and collectively, these tag errors had little effect on the calculation of the vertically integrated water vapor content. However, individual large lag errors occurred with dramatic changes in the environment, such as near the surface or at the top of the boundary layer. Dual-sonde flights showed mean instrument error comparable to lag error and had little effect on the calculation of the columnar water vapor content. A hypothetical consistent error of 5% in the measurement of relative humidity in a dry environ...

AND/OR graph representation of assembly plans

A compact representation of all possible assembly plans of a given product using AND/OR graphs is presented. Such a representation forms the basis for efficient planning algorithms that make possible an increase in assembly system flexibility by allowing an intelligent robot to pick a course of action according to instantaneous conditions. The AND/OR graph is equivalent to a state transition graph but requires fewer nodes and simplifies the search for feasible plans. Three applications are discussed: the preselection of the best assembly plan, the recovery from execution errors, and the opportunistic scheduling of tasks. A hypothetical error situation in the assembly of the four-part assembly is discussed to show how a bottom-up search of the AND/OR graph leads to an efficient recovery. The scheduling efficiency using this representation is compared with fixed sequence and precedence graph representations. >

Spatial rainfall estimation by linear and non-linear co-kriging of radar-rainfall and raingage data

The feasibility of linear and nonlinear geostatistical estimation techniques for optimal merging of rainfall data from raingage and radar observations is investigated in this study by use of controlled numerical experiments. Synthetic radar and raingage data are generated with their hypothetical error structures that explicitly account for sampling characteristics of the two sensors. Numerically simulated rainfall fields considered to be ground-truth fields on 4×4 km grids are used in the generation of radar and raingage observations. Ground-truth rainfall fields consist of generated rainfall fields with various climatic characteristics that preserve the space-time covariance function of rainfall events in extratropical cyclonic storms. Optimal mean areal precipitation estimates are obtained based on the minimum variance, unbiased property of kriging techniques under the second order homogeneity assumption of rainfall fields. The evaluation of estimated rainfall fields is done based on the refinement of spatial predictability over what would be provided from each sensor individually. Attention is mainly given to removal of measurement error and bias that are synthetically introduced to radar measurements. The influence of raingage network density on estimated rainfall fields is also examined.