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At least 973 records · Page 54Linked to original sources
PubMed2005

A novel approach for incremental uncertainty rule generation from databases with missing values handling: application to dynamic medical databases.

Current approaches for mining association rules usually assume that the mining is performed in a static database, where the problem of missing attribute values does not practically exist. However, these assumptions are not preserved in some medical databases, like in a home care system. In this paper, a novel uncertainty rule algorithm is illustrated, namely URG-2 (Uncertainty Rule Generator), which addresses the problem of mining dynamic databases containing missing values. This algorithm requires only one pass from the initial dataset in order to generate the item set, while new metrics corresponding to the notion of Support and Confidence are used. URG-2 was evaluated over two medical databases, introducing randomly multiple missing values for each record's attribute (rate: 5-20% by 5% increments) in the initial dataset. Compared with the classical approach (records with missing values are ignored), the proposed algorithm was more robust in mining rules from datasets containing missing values. In all cases, the difference in preserving the initial rules ranged between 30% and 60% in favour of URG-2. Moreover, due to its incremental nature, URG-2 saved over 90% of the time required for thorough re-mining. Thus, the proposed algorithm can offer a preferable solution for mining in dynamic relational databases.

Algorithms↗
PubMed2006

Uncertainty analysis of relative biological effectiveness of alpha-radiation for human lung exposure.

Assessment of relative biological effectiveness (RBE) for a radiation in the cases of inhalation of radon progeny and incorporation of plutonium in lung is based on simulation of lung cancer radiation risk for alpha and external reference types of radiation. Specific radiation risk models developed on the results of direct epidemiological studies are used for simulation. These include published risk models for nuclear workers of the Mayak facilities in the former Soviet Union exposed to incorporated plutonium (Kreisheimer et al., 2003; Gilbert et al., 2004) and underground miners exposed to radon progenies (BEIR VI, 1999). Additionally, a lung cancer risk model is developed for a case of population indoor radon exposure. Lung cancer risk related to external exposure is estimated using the risk model developed for the analyses of Japanese atomic bomb survivors (Preston et al., 2003). Uncertainties of risk models parameters are considered and the uncertainties of RBE are estimated using the results of lifetime lung cancer risk simulation, which is done implementing a Monte Carlo approach. Estimated median value of RBE in case of indoor radon exposure is 1.5 with 90% range 0.4-7. In the case of the two models developed by BEIR VI for lung cancer risk due to radon exposure in underground miners, the median values of RBE are 2.1 and 4.4 with 90% ranges 0.3-17 and 0.7-45, respectively. The two different models for lung cancer risk related to plutonium exposure resulted in close estimates of RBE: median value of 12 and 13 with 90% range 4-104 and 4-136, respectively.

Adult↗
PubMedDate not supplied

Developing scientific and policy methods that support precautionary action in the face of uncertainty--the Institute of Medicine Committee on Agent Orange.

To be precautionary, decisions must be made to prevent the impacts of potentially harmful activities even though the nature and magnitude of harm have not been proven scientifically. The Institute of Medicine's Committee on the Health Effects in Vietnam Veterans of Exposures to Herbicides provides a novel example of science and policy structures that support precautionary action in the face of uncertainty. What makes this example unique is the clear set of precautionary decision rules that lowered the standard for evidence, which formed the basis for policy. These rules, established by Congress, strongly influenced the way scientific information was weighed and the subsequent compensation decisions. They encouraged committee members to think outside the confines of their disciplines and develop new tools and methods to fit their unique mandate. The result was a methodology, supported by strong institutional structures, that allowed scientists to discuss the evidence as a whole, reach decisions as a group, and clarify uncertainties.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed2004

Uncertainties in the pathogenesis of adult dermatomyositis.

PURPOSE OF REVIEW: Dermatomyositis is an inflammatory disorder of muscle affecting both children and adults. The pathogenesis of adult dermatomyositis is reviewed here, with particular attention to gaps and uncertainties in our current understanding of this disease, in order to focus attention on the outstanding research questions with regard to disease mechanisms. RECENT FINDINGS: The conceptual model of the pathophysiology of dermatomyositis has been based on work extending back over at least 35 years, with important findings related to the deposition of membrane attack complex, the character of the inflammatory infiltrate, and the primacy of capillary abnormalities established over 10 years ago. The lack of significant additions to the understanding of this disease over the past few years suggests a state of contentment with current knowledge. Accordingly, we emphasize the uncertainties of this knowledge and the need for re-addressing some of its basic tenets. SUMMARY: Although evidence remains strong that dermatomyositis is a disorder with an early involvement of the capillaries, the concept that it results from an antibody-mediated attack upon the endothelium is uncertain. It is not clear whether membrane attack complex is activated by antibody-dependent or independent means, whether or not intramuscular B cells are antigen specific and synthesize significant quantities of antibodies, whether the presence of tubuloreticular inclusions precedes, follows, or is independent of membrane attack complex deposition, what is the mechanism of perifascicular atrophy, and what is the relationship of dermatomyositis to systemic lupus erythematosus.

Adult↗
PubMed2002

Managing uncertainty: information and insurance under the risk of starvation.

In an uncertain world, animals face both unexpected opportunities and danger. Such outcomes can select for two potential strategies: collecting information to reduce uncertainty, or insuring against it. We investigate the relative value of information and insurance (energy reserves) under starvation risk by offering model foragers a choice between constant and varying food sources over finite foraging bouts. We show that sampling the variable option (choosing it when it is not expected to be good) should decline both with lower reserves and late in foraging bouts; in order to be able to reap the reduction in uncertainty associated with exploiting a variable resource effectively, foragers must be able to afford and compensate for an initial increase in the risk of an energetic shortfall associated with choosing the option when it is bad. Consequently, expected exploitation of the varying option increases as it becomes less variable, and when the overall risk of energetic shortfall is reduced. In addition, little activity on the variable alternative is expected until reserves are built up early in a foraging bout. This indicates that gathering information is a luxury while insurance is a necessity, at least when foraging on stochastic and variable food under the risk of starvation.

Animals↗
PubMed2004

Quantification of variability and uncertainty for censored data sets and application to air toxic emission factors.

Many environmental data sets, such as for air toxic emission factors, contain several values reported only as below detection limit. Such data sets are referred to as "censored." Typical approaches to dealing with the censored data sets include replacing censored values with arbitrary values of zero, one-half of the detection limit, or the detection limit. Here, an approach to quantification of the variability and uncertainty of censored data sets is demonstrated. Empirical bootstrap simulation is used to simulate censored bootstrap samples from the original data. Maximum likelihood estimation (MLE) is used to fit parametric probability distributions to each bootstrap sample, thereby specifying alternative estimates of the unknown population distribution of the censored data sets. Sampling distributions for uncertainty in statistics such as the mean, median, and percentile are calculated. The robustness of the method was tested by application to different degrees of censoring, sample sizes, coefficients of variation, and numbers of detection limits. Lognormal, gamma, and Weibull distributions were evaluated. The reliability of using this method to estimate the mean is evaluated by averaging the best estimated means of 20 cases for small sample size of 20. The confidence intervals for distribution percentiles estimated with bootstrap/MLE method compared favorably to results obtained with the nonparametric Kaplan-Meier method. The bootstrap/MLE method is illustrated via an application to an empirical air toxic emission factor data set.

Air↗
PubMed2004

Evidence-based uncertainty in mental health nursing.

The drive towards evidence-based practice is part of a modern reflective and caring service. However there is a paradox at the heart of the notion of evidence-based care. In order to perform any systemized examination of treatment there has to be a conscious acknowledgement of uncertainty about that treatment. This is uncomfortable and when research does find evidence in favour of a treatment, there is a relief and a return to conviction about what is the best. The paradox is that it seems the most valued research practices are predicated on generalizations about patient treatments and categories. However, nursing care is based on the notion of the uniqueness of the patient and the nurse-patient relationship. Sometimes it is necessary to address the particular and not to rush to generalizations and certainty. The psychoanalytic framework promotes a capacity to tolerate uncertainty and provides a model for understanding conflicting feelings, which can occur within the nurse-patient relationship. The author proposes the psychoanalytic observational method as an adjunct to other research methods. This method places certain kinds of evidence within the rubric of evidence-based nursing practice. The evidence collected in this method is the evidence of the conscious and unconscious experience within the nurse-patient relationship. The author will describe and argue for the place of this research method within the canon of other more widely practised methods within mental health practice. She will propose that for safe practice it is necessary to value and examine the veracity of the feelings and tacit understanding of the nurse. She contends that the current climate of excessive bureaucracy and persecutory risk management is having a damaging effect on both the research process and effective nursing care.

Evidence-Based Medicine↗
PubMed2005

Exploring clinician uncertainty in the diagnosis and treatment of attention deficit hyperactivity disorder.

Based upon analyses of interview data collected from twenty-six clinician respondents, this study explores two facets of clinician uncertainty related to the diagnosis and treatment of attention deficit hyperactivity disorder (ADHD) in children. First, this study explores clinician reservations about the diagnostic validity of ADHD as it is described by the American Psychiatric Association (1994) in DSM IV. Second, this study explores clinician ambivalence regarding the physical and social-psychological side-effects of stimulant medications, such as Ritalin. In applying the sociological discussions that address uncertainty in clinical settings and through reviewing a sizable cross-section of the popular and research-oriented literature demonstrating the contentious nature of the ADHD phenomenon, this study illustrates that clinicians do not practice within a vacuum, but are instead largely affected by the marked scepticism that surrounds ADHD. In being affected by this scepticism, it is concluded that clinicians who assess and treat ADHD are autonomous in how they interpret the diagnostic and treatment protocols for this mental disorder.

Attention Deficit Disorder with Hyperactivity↗
PubMed2006

To cope with uncertainty: stroke patients' use of temporal models in narratives.

Stroke victims have to cope with a disrupted autobiography and anxiety because of an uncertain future. Professionals share this uncertainty. The patients reveal their experiences in narratives, and when they try to regain coherence and confidence in life, they use narratives in the reconstructions. Because they have a temporal problem, time might be an important issue in these narratives. The aim of this study was to elucidate the use of time models in stroke patients' narratives. Nineteen stroke patients, who had recently been discharged to their homes after the stroke, accepted to participate in the study. Their age span was between 56 and 89 years. They had lived active urban lives before the stroke, and poststroke only three had more serious physical impairment, and none was demented. They were asked to talk about their present life and their conceptions of future life. The interviews were audio-taped and transcribed verbatim and narratives that referred to temporal aspects were thematically analysed with reference to narrative time models. The stroke accident had caused an autobiographical disruption and a temporal split because of a new awareness of human temporality and an uncertainty of the future. Confronted with these problems of time, the stroke victims constructed narratives based on the time models: time cycles and dissolution of time limits, exchange of time and exclusion from time. Hence, the time models worked as tools when the stroke victims re-established coherence in their present and future life. Stroke patients handled an uncertain future by using temporal models in their narratives. Professionals can support stroke patients by reinforcing these models.

Adaptation, Psychological↗
PubMed2006

Evaluation of uncertainty predictions and dose output for model-based dose calculations for megavoltage photon beams.

In many radiotherapy clinics an independent verification of the number of monitor units (MU) used to deliver the prescribed dose to the target volume is performed prior to the treatment start. Traditionally this has been done by using methods mainly based on empirical factors which, at least to some extent, try to separate the influence from input parameters such as field size, depth, distance, etc. The growing complexity of modern treatment techniques does however make this approach increasingly difficult, both in terms of practical application and in terms of the reliability of the results. In the present work the performance of a model-based approach, describing the influence from different input parameters through actual modeling of the physical effects, has been investigated in detail. The investigated model is based on two components related to megavoltage photon beams; one describing the exiting energy fluence per delivered MU, and a second component describing the dose deposition through a pencil kernel algorithm solely based on a measured beam quality index. Together with the output calculations, the basis of a method aiming to predict the inherent calculation uncertainties in individual treatment setups has been developed. This has all emerged from the intention of creating a clinical dose/MU verification tool that requires an absolute minimum of commissioned input data. This evaluation was focused on irregular field shapes and performed through comparison with output factors measured at 5, 10, and 20 cm depth in ten multileaf collimated fields on four different linear accelerators with varying multileaf collimator designs. The measurements were performed both in air and in water and the results of the two components of the model were evaluated separately and combined. When compared with the corresponding measurements the resulting deviations in the calculated output factors were in most cases smaller than 1% and in all cases smaller than 1.7%. The distribution describing the calculation errors in the total dose output has a mean value of -0.04% and a standard deviation of 0.47%. In the dose calculations a previously developed correction of the pencil kernel was applied that managed to contract the error distribution considerably. A detailed analysis of the predicted uncertainties versus the observed deviations suggests that the predictions indeed can be used as a basis for creating action levels and tracking dose calculation errors in homogeneous media.

Air↗
PubMed2006

Quantifying how tests reduce diagnostic uncertainty.

BACKGROUND: Diagnostic tests are commonly evaluated from sensitivity and specificity, which are robust and independent of prevalence, but clinically not intuitive. Many clinicians prefer to use positive and negative predictive values (PPV and NPV), but they are frequently applied as if they are independent of prevalence, whereas this may make an important difference. METHODS AND RESULTS: We present graphs that allow easy reference to appropriate values and demonstrate that PPV and NPV are not independent of prevalence. PPV and NPV figures reflect the prior probability of the case having a positive diagnosis, estimated clinically from the history, examination and other results, as well as the impact of the test result. To avoid the common error of allowing for prior probability twice, and to interpret the impact of the test result alone, we present graphs of the proportionate reduction in uncertainty score (PRU), calculated from sensitivity, specificity and prevalence. These plots show the extent to which either a positive or negative test result affects the remaining degree of uncertainty about a diagnosis in either direction, according to likely clinical prevalence. CONCLUSIONS: PRU plots demonstrate the discriminatory value of tests more clearly than sensitivity and specificity from which they are derived, and should be published alongside them.

Child↗
PubMed2004

Satisfaction of the uncertainty principle in cancer clinical trials: retrospective cohort analysis.

OBJECTIVE: To assess whether publicly funded adult cancer trials satisfy the uncertainty principle, which states that physicians should enroll a patient in a trial only if they are substantially uncertain which of the treatments in the trial is most appropriate for the patient. This principle is violated if trials systematically favour either the experimental or the standard treatment. DESIGN: Retrospective cohort study of completed cancer trials, with randomisation as the unit of analysis. SETTING: Two cooperative research groups in the United States. STUDIES INCLUDED: 93 phase III randomised trials (103 randomisations) that completed recruitment of patients between 1981 and 1995. MAIN OUTCOME MEASURES: Whether the randomisation favoured the experimental treatment, the standard treatment, or neither treatment; effect size (outcome of the experimental treatment compared with outcome of the standard treatment) for each randomisation. RESULTS: Three randomisations (3%) favoured the standard treatment, 70 (68%) found no significant difference between treatments, and 30 (29%) favoured the experimental treatment. The average effect size was 1.20 (95% confidence interval 1.13 to 1.28), reflecting a slight advantage for the experimental treatment. CONCLUSIONS: In cooperative group trials in adults with cancer, there is a measurable average improvement in disease control associated with assignment to the experimental rather than the standard arm. However, the heterogeneity of outcomes and the small magnitude of the advantage suggest that, as a group, these trials satisfy the uncertainty principle.

Clinical Trials, Phase III as Topic↗
PubMedDate not supplied

Implications of cancer staging uncertainties in radiation therapy decisions.

INTRODUCTION: Radiation therapy (RT) for cancer is a critical medical procedure that occurs in a complex environment involving numerous health professionals, hardware, software, and equipment. Uncertainties and potential incidents can lead to inappropriate administration of radiation to patients, with sometimes catastrophic consequences such as premature death or appreciably impaired quality of life. The authors evaluate the impact of incorrectly staging (i.e., estimation of extent of cancer) breast cancer patients and resulting inappropriate treatment decisions. METHODS: The authors employ analytic and simulation methods in an influence-diagram framework to estimate the probability of incorrect staging and treatment decisions. As inputs, they use a combination of literature information on the accuracy and precision of pathology and tests as well as expert judgment. Sensitivity and value-of-information analyses are conducted to identify important uncertainties. RESULTS AND CONCLUSIONS: The authors find a small but nontrivial probability that breast cancer patients will be incorrectly staged and thus may be subjected to inappropriate treatment. Results are sensitive to a number of variables, and some routinely used tests for metastasis have very limited information value. This work has implications for the methods used in cancer staging, and the methods are generalizable for quantitative risk assessment of treatment errors.

Breast Neoplasms↗
PubMed2003

The experience of uncertainty for individuals with HIV/AIDS and the palliative care paradigm.

This small qualitative study investigated the lived experience of individuals with HIV/AIDS, exploring the uncertainty related to episodes of life-threatening illness followed by recovery, 'revival'. The themes that emerged related to the unpredictability of when death would occur. The participants described the dilemma of living with a chronic illness with a totally unpredictable disease trajectory. Following periods of being extremely unwell, individuals would then recover and experience periods of relative well-being, only to succumb to another infection later. The findings highlighted the uncertainty that pervades all aspects of HIV-positive individuals' lives as they face death. An awareness of this may be important in those offering palliative care to those with HIV/AIDS.

Adaptation, Psychological↗
PubMed2005

Displaying uncertainty: investigating the effects of display format and specificity.

We conducted four studies regarding the representation of probabilistic information. Experiments 1 through 3 compared performance on a simulated stock purchase task, in which information regarding stock profitability was probabilistic. Two variables were manipulated: display format for probabilistic information (blurred and colored icons, linguistic phrases, numeric expressions, and combinations) and specificity level (in which the number and size of discrete steps into which the probabilistic information was mapped differed). Results indicated few performance differences attributable to display format; however, performance did improve with greater specificity. Experiment 4, in which participants generated membership functions corresponding to three display formats, found a high degree of similarity in functions across formats and participants and a strong relationship between the shape of the membership function and the intended meaning of the representation. These results indicate that participants can successfully interpret nonnumeric representations of uncertainty and can use such representations in a manner similar to the way numeric expressions are used in a decision-making task. Actual or potential applications of this research include the use of graphical representations of uncertainty in systems such as command and control and situation displays.

Adult↗
PubMed2005

Manufacturing uncertainty: contested science and the protection of the public's health and environment.

Opponents of public health and environmental regulations often try to "manufacture uncertainty" by questioning the validity of scientific evidence on which the regulations are based. Though most identified with the tobacco industry, this strategy has also been used by producers of other hazardous products. Its proponents use the label "junk science" to ridicule research that threatens powerful interests. This strategy of manufacturing uncertainty is antithetical to the public health principle that decisions be made using the best evidence available. The public health system must ensure that scientific evidence is evaluated in a manner that assures the public's health and environment will be adequately protected.

Environmental Exposure↗
PubMed2006

Risk- and robustness-based solutions to a multi-objective water distribution system rehabilitation problem under uncertainty .

The water distribution system (WDS) rehabilitation problem is defined here as a multi-objective optimisation problem under uncertainty. Two alternative problem formulations are considered. The first objective in both approaches is to minimise the total rehabilitation cost. The second objective is to either maximise the overall WDS robustness or to minimise the total WDS risk. The WDS robustness is defined as the probability of simultaneously satisfying minimum pressure head constraints at all nodes in the network. Total risk is defined as the sum of nodal risks, where nodal risk is defined as the product of the probability of pressure failure at that node and consequence of such failure. Decision variables are the alternative rehabilitation options for each pipe in the network. The only source of uncertainty is the future water consumption. Uncertain demands are modelled using any probability density functions (PDFs) assigned in the problem formulation phase. The corresponding PDFs of the analysed nodal heads are calculated using the Latin Hypercube sampling technique. The optimal rehabilitation problem is solved using the newly developed rNSGAII method which is a modification of the well-known NSGAII optimisation algorithm. In rNSGAII a small number of demand samples are used for each fitness evaluation leading to significant computational savings when compared to the full sampling approach. The two alternative approaches are tested, verified and their performance compared on the New York tunnels case study. The results obtained demonstrate that both new methodologies are capable of identifying the robust (near) Pareto optimal fronts while making significant computational savings.

Facility Design and Construction↗
PubMed2005

Screening for vertebrobasilar insufficiency in patients with neck pain: manual therapy decision-making in the presence of uncertainty.

Growing evidence supports the effectiveness of manual therapy interventions in patients with neck pain; however, considerable attention has also been afforded to the potential risks such as vertebrobasilar insufficiency (VBI). Despite the existence of guidelines advocating specific screening procedures, research does not support the ability to accurately identify patients at risk. The logical question becomes, "How does one proceed in the absence of certainty?" Given the lack of clear direction for decision making in the peer-reviewed literature, this commentary discusses the uncertainties that exist regarding the ability to identify patients at risk for VBI. The authors hope that this commentary adds additional perspective on manual therapy decision-making strategies in the presence of uncertainty.

Humans↗