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Search Results: 1 - 10 of 173426 matches for " Gary E. Davis "
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The Turtleback Diagram for Conditional Probability  [PDF]
Donghui Yan, Gary E. Davis
Open Journal of Statistics (OJS) , 2018, DOI: 10.4236/ojs.2018.84045
Abstract: We elaborate on an alternative representation of conditional probability to the usual tree diagram. We term the representation “turtleback diagram” for its resemblance to the pattern on turtle shells. Adopting the set theoretic view of events and the sample space, the turtleback diagram uses elements from Venn diagrams—set intersection, complement and partition—for conditioning, with the additional notion that the area of a set indicates probability whereas the ratio of areas for conditional probability. Once parts of the diagram are drawn and properly labeled, the calculation of conditional probability involves only simple arithmetic on the area of relevant sets. We discuss turtleback diagrams in relation to other visual representations of conditional probability, and detail several scenarios in which turtleback diagrams prove useful. By the equivalence of recursive space partition and the tree, the turtleback diagram is seen to be equally expressive as the tree diagram for abstract concepts. We also provide empirical data on the use of turtleback diagrams with undergraduate students in elementary statistics or probability courses.
Individual gain and engagement with mathematical understanding
Mercedes A. McGowen,Gary E. Davis
Mathematics , 2014,
Abstract: We examine a measure of individual student gain by preservice elementary teachers, related to Richard Hakes use of mean gain in the study of reform classes in undergraduate physics. The gain statistic assesses the amount individual students increase their test scores from initial test to final test, as a proportion of the possible increase for each student. We examine the written work in mathematics classes of preservice elementary teachers with very high gain and those with very low gain and show that these groups exhibit distinct psychological attitudes and dispositions to learning mathematics. We show a statistically significant, small, increase in average gain when course goals focus on patterns, connections, and meaning making in mathematics. A common belief is that students with low initial test scores will have higher gains, and students with high initial-test scores will have lower gains. We show that this is not correct for a cohort of preservice elementary teachers.
Using Bayesian Networks to Identify the Causal Effect of Speeding in Individual Vehicle/Pedestrian Collisions
Gary A. Davis
Computer Science , 2013,
Abstract: On roads showing significant violations of posted speed limits, one measure of the safety effect of speeding is the difference between the road's actual accident count and the count that would have occurred if the posted speed limit had been strictly obeyed. An estimate of this accident reduction can be had by computing the probability that speeding was a necessary condition for each of set of accidents. This is an instance of assessing individual probabilities of causation, which is generally not possible absent prior knowledge of causal structure. For traffic accidents such prior knowledge is often available and this paper illustrates how, for a commonly occurring class of vehicle/pedestrian accidents, approaches to uncertainty and causal analyses appearing in the accident reconstruction literature can be unified using Bayesian networks. Measured skidmarks, pedestrian throw distances, and pedestrian injury severity are treated as evidence, and using the Gibbs Sampling routine BUGS, the posterior probability distribution over exogenous variables, such as the vehicle's initial speed, location, and driver reaction time, is computed. This posterior distribution is then used to compute the "probability of necessity" for speeding.
The Scope and Limits of Simulation in Cognitive Models
Ernest Davis,Gary Marcus
Computer Science , 2015,
Abstract: It has been proposed that human physical reasoning consists largely of running "physics engines in the head" in which the future trajectory of the physical system under consideration is computed precisely using accurate scientific theories. In such models, uncertainty and incomplete knowledge is dealt with by sampling probabilistically over the space of possible trajectories ("Monte Carlo simulation"). We argue that such simulation-based models are too weak, in that there are many important aspects of human physical reasoning that cannot be carried out this way, or can only be carried out very inefficiently; and too strong, in that humans make large systematic errors that the models cannot account for. We conclude that simulation-based reasoning makes up at most a small part of a larger system that encompasses a wide range of additional cognitive processes.
Disruption of the Putative Vascular Leak Peptide Sequence in the Stabilized Ricin Vaccine Candidate RTA1-33/44-198
Laszlo Janosi,Jaimee R. Compton,Patricia M. Legler,Keith E. Steele,Jon M. Davis,Gary R. Matyas,Charles B. Millard
Toxins , 2013, DOI: 10.3390/toxins5020224
Abstract: Vitetta and colleagues identified and characterized a putative vascular leak peptide (VLP) consensus sequence in recombinant ricin toxin A-chain (RTA) that contributed to dose-limiting human toxicity when RTA was administered intravenously in large quantities during chemotherapy. We disrupted this potentially toxic site within the more stable RTA1-33/44-198 vaccine immunogen and determined the impact of these mutations on protein stability, structure and protective immunogenicity using an experimental intranasal ricin challenge model in BALB/c mice to determine if the mutations were compatible. Single amino acid substitutions at the positions corresponding with RTA D75 (to A, or N) and V76 (to I, or M) had minor effects on the apparent protein melting temperature of RTA1-33/44-198 but all four variants retained greater apparent stability than the parent RTA. Moreover, each VLP(?) variant tested provided protection comparable with that of RTA1-33/44-198 against supralethal intranasal ricin challenge as judged by animal survival and several biomarkers. To understand better how VLP substitutions and mutations near the VLP site impact epitope structure, we introduced a previously described thermal stabilizing disulfide bond (R48C/T77C) along with the D75N or V76I substitutions in RTA1-33/44-198. The D75N mutation was compatible with the adjacent stabilizing R48C/T77C disulfide bond and the T m was unaffected, whereas the V76I mutation was less compatible with the adjacent disulfide bond involving C77. A crystal structure of the RTA1-33/44-198 R48C/T77C/D75N variant showed that the structural integrity of the immunogen was largely conserved and that a stable immunogen could be produced from E. coli. We conclude that it is feasible to disrupt the VLP site in RTA1-33/44-198 with little or no impact on apparent protein stability or protective efficacy in mice and such variants can be stabilized further by introduction of a disulfide bond.
A comprehensive cardiovascular disease lifestyle treatment controlled trial among high-risk African Americans  [PDF]
Sharon K. Davis, Rakale Quarells, Gary H. Gibbons
Open Journal of Preventive Medicine (OJPM) , 2013, DOI: 10.4236/ojpm.2013.39071

Background: The purpose of this study was to assess the effects of a comprehensive lifestyle intervention on modifiable cardiovascular risk factors among high-risk African Americans. Methods: The study included a randomized treatment/controlled intervention trial among 136 African Americans residing in Atlanta, GA who were overweight and had elevated blood pressure. The treatment group was exposed to 3-months of a multi-component intervention and the control to an abbreviated 6-week intervention after the completion of the treatment group’s intervention. The main outcomes included mean systolic blood pressure (SBP), mean diastolic blood pressure (DBP), mean waist circumference, mean body mass index (BMI), mean number of times exercise per week, mean number of servings of fruits and vegetables per day, and mean level of daily stress. Data were collected at baseline and at 6-month follow-up. Separate linear regressions were used with an established significance level of P < 0.05. Results: Results revealed significant net improvement in treatment group when compared to controls in waist circumference, BMI, times weekly exercise, servings of fruit and vegetables per day (P < 0.001, 0.04, 0.02, 0.002, respectively). Diastolic blood pressure also significantly improved within the treatment group for overall hypertensives from baseline to 6-month follow-up (90.9 mmHg to 83.1 mmHg, P = 0.002). Conclusion: These results show that a comprehensive lifestyle intervention can improve cardiovascular risk factor profile among high risk African Americans. Caregivers should encourage patients to participate in such programs and public health policymakers should allocate resources to

Premorbid Use of Clopidogrel Portends Worse Outcomes in Patients Treated Surgically for Intracranial Hemorrhage  [PDF]
Eric Marvin, Aaron Danison, Greg Davis, Zev Elias, Gary Simonds
Open Journal of Modern Neurosurgery (OJMN) , 2014, DOI: 10.4236/ojmn.2014.44030
Abstract: Background: Widespread use of antiplatelet and anticoagulation medications (APACs) can be a difficult challenge in the presence of a neurosurgical emergency. Premorbid use of APACs, particularly clopidogrel, has been shown to affect outcomes in patients with stroke and traumatic brain injury. Objective: We hypothesized that pre-morbid clopidogrel use in patients with intracranial hemorrhage necessitating surgical intervention would lead to a greater risk of death and need for re-operation than those taking other APACs. Methods: Retrospective single institution review was conducted from January, 2010 through November, 2012 for intracranial hemorrhages necessitating surgical evacuation. Acute, subacute and chronic subdural, epidural and intraparenchymal hemorrhages were included. Results: 185 of 410 patients that required surgery for intracranial hemorrhage were on APACs. Overall mortality rate was 33%, with a 37% mortality rate in the APAC group. Overall reoperation rate was 7.5%, and 13% in the APAC group. Chi-square testing demonstrated significance between mortality and clopidogrel use (p = 0.0038), but not in APAC, warfarin or aspirin groups. There was statistical significance between the need for reoperation and APAC use (p = 0.002), aspirin use (p = 0.0097), and clopidogrel use (p = 0.0152), but not warfarin. Multivariate regression demonstrated only clopidogrel use is associated with higher mortality (p = 0.05) and need for reoperation (p = 0.0206). Conclusion: APAC use in the setting of intracranial hemorrhage necessitating surgical evacuation have higher intraoperative blood loss, need for transfusion and risk for adverse cardiac events. Premorbid clopidogrel use is associated with an increased risk in mortality and need for reoperation.
Risk and Uncertainty in Anesthesia  [PDF]
Roman Pohorecki,Gary E. Hill
Open Journal of Anesthesiology (OJAnes) , 2013, DOI: 10.4236/ojanes.2013.37072
Abstract: This article discusses risk and uncertainty, both stochastic and epistemic, as it applies to anesthesia. It shows the difficulty in quantifying risk of individual case and the somewhat arbitrary and even incorrect and naive assignment of risk in individual patient care management. Effective and honest communication remains at the core of physician-patient relationship in discussing, evaluating and managing the individual case for optimum outcome as well as patients’ and their families' satisfaction and understanding.
Risk and Uncertainty in Anesthesia  [PDF]
Roman Pohorecki, Gary E. Hill
Open Journal of Anesthesiology (OJAnes) , 2013, DOI: 10.4236/ojanes.2013.37072

This article discusses risk and uncertainty, both stochastic and epistemic, as it applies to anesthesia. It shows the difficulty in quantifying risk of individual case and the somewhat arbitrary and even incorrect and naive assignment of risk in individual patient care management. Effective and honest communication remains at the core of physician-patient relationship in discussing, evaluating and managing the individual case for optimum outcome as well as patients’ and their families' satisfaction and understanding.

Order of Magnitude Comparisons of Distance
E. Davis
Computer Science , 2011, DOI: 10.1613/jair.520
Abstract: Order of magnitude reasoning - reasoning by rough comparisons of the sizes of quantities - is often called 'back of the envelope calculation', with the implication that the calculations are quick though approximate. This paper exhibits an interesting class of constraint sets in which order of magnitude reasoning is demonstrably fast. Specifically, we present a polynomial-time algorithm that can solve a set of constraints of the form 'Points a and b are much closer together than points c and d.' We prove that this algorithm can be applied if `much closer together' is interpreted either as referring to an infinite difference in scale or as referring to a finite difference in scale, as long as the difference in scale is greater than the number of variables in the constraint set. We also prove that the first-order theory over such constraints is decidable.
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