Bridging Jeffrey's Rule, AGM Revision and Dempster Conditioning in the Theory of Evidence

Belief revision characterizes the process of revising an agent’s beliefs when receiving new evidence. In the field of artificial intelligence, revision strategies have been extensively studied in the context of logic-based formalisms and probability kinematics. However, so far there is not much literature on this topic in evidence theory. In contrast, combination rules proposed so far in the theory of evidence, especially Dempster rule, are symmetric. They rely on a basic assumption, that is, pieces of evidence being combined are considered to be on a par, i.e. play the same role. When one source of evidence is less reliable than another, it is possible to discount it and then a symmetric combination operation
is still used. In the case of revision, the idea is to let prior knowledge of an agent be altered by some input information. The change problem is thus intrinsically asymmetric. Assuming the input information is reliable, it should be retained whilst the prior information should be changed minimally to that effect. To deal with this issue, this paper defines the notion of revision for the theory of evidence in such a way as to bring together probabilistic and logical views. Several revision rules previously proposed are reviewed and we advocate one of them as better corresponding to the idea of revision. It is extended to cope with inconsistency between prior and input information. It reduces to Dempster
rule of combination, just like revision in the sense of Alchourron, Gardenfors, and Makinson (AGM) reduces to expansion, when the input is strongly consistent with the prior belief function. Properties of this revision rule are also investigated and it is shown to generalize Jeffrey’s rule of updating, Dempster rule of conditioning and a form of AGM revision.

Choice of contracts in the British National Health Service: An empirical study

Following major reforms of the British National Health Service (NHS) in 1990, the roles of purchasing and providing health services were separated, with the relationship between purchasers and providers governed by contracts. Using a mixed multinomial logit analysis, we show how this policy shift led to a selection of contracts that is consistent with the predictions of a simple model, based on contract theory, in which the characteristics of the health services being purchased and of the contracting parties influence the choice of contract form. The paper thus provides evidence in support of the practical relevance of theory in understanding health care market reform. © 2008 Elsevier B.V. All rights reserved.

The principles and practice of interpreting cardiac rhythm strips: a seven-step model

This open learning zone article examines the cardiac cycle and the interpretation of cardiac rhythm strips. The article begins with a brief revision of related physiology followed by a description of normal sinus rhythm and the main cardiac rhythm abnormalities. The article concludes by providing easy to follow steps for use in the interpretation of cardiac rhythm strips with practice examples presented in the CPD task section.

Edaphic factors affecting the toxicity and accumulation of arsenate in the earthworm Lumbricus terrestris

The toxicity and accumulation of arsenate was determined in the earthworm Lumbricus terrestris in soil from different layers of a forest profile. Toxicity increased fourfold between 2 and 10 d. Edaphic factors (pH, soil organic matter, and depth in soil profile) also affected toxicity with a three fold decrease in the concentration that causes 50% mortality with increasing depth in soil (from 0-70 mm to 500-700 mm). In a 4-d exposure study, there was no evidence of arsenic bioconcentration in earthworm tissue, although bioaccumulation was occurring. There was a considerable difference in tissue residues between living and dead earthworms, with dead worms having higher concentrations. This difference was dependent on both soil arsenate concentration and on soil type. Over a wide range of soil arsenate concentrations, earthworm arsenic residues are homeostatically maintained in living worms, but this homeostasis breaks down during death. Alternatively, equilibration with soil residues may occur via accumulation after death. In long-term accumulation studies in soils dosed with a sublethal arsenate concentration (40 μg/g dry weight), bioconcentration of arsenate did not occur until day 12, after which earthworm concentrations rose steadily above the soil concentration, with residues in worms three fold higher than soil concentrations by the termination of the study (23 d). This bioconcentration only occurred in depurated worms over the time period of the study. Initially, depurated worms had lower arsenic concentrations than undepurated until tissue concentrations were equivalent to the soil concentration. Once tissue concentration was greater than soil concentration, depurated worms had higher arsenic residues than undepurated.

Outcomes of surgical bleb revision for complications of trabeculectomy.

OBJECTIVE: To describe the results of revision surgery for complications of trabeculectomy in a case series from an academic glaucoma service. DESIGN: Retrospective case series. PARTICIPANTS: A total of 177 eyes of 167 adult patients who underwent revision of trabeculectomy at the Wilmer Eye Institute between 1994 and 2007. METHODS: Three indications for surgery were identified: hypotony without leak, bleb leak, and bleb dysesthesia. Revision was deemed successful when all of the following were true: the primary indication was eliminated, further intraocular pressure (IOP)-lowering surgery was not required, no major complication occurred, and a new bleb-related problem did not develop. Patients with less than 3 months of follow-up were excluded unless failure occurred earlier. Surgical procedures included variations on excision of thin or leaking conjunctiva with advancement. MAIN OUTCOME MEASURES: Change in IOP, change in visual acuity, need for further IOP-lowering surgery, and complications after bleb revision. RESULTS: Subjects' mean age was 67+/-14 years, 54% were female, and mean follow-up was 2.8+/-2.7 years, with a mean interval from trabeculectomy to revision of 3.5+/-3.7 years. Overall success rate was 63% (112/177), which was slightly higher for leak repair (65%; 64/98) and hypotony (63%; 32/51) than for dysesthesia (57%; 16/28) indications. By Kaplan-Meier analysis, overall cumulative success rates at 1, 2, 5, and 10 years after bleb revision were 80%, 75%, 50%, and 41%, respectively. IOP and visual acuity improved significantly in both hypotony and leak groups (P values ranging from 0.004 to <0.0001). Additional IOP-lowering surgery was required in 9%. In multivariate regression analysis adjusting for age, gender, and number of prior surgeries, patients with glaucoma other than primary open-angle glaucoma were twice as likely to have failed bleb revision. CONCLUSIONS: Surgical bleb revision often provides successful resolution of bleb-related complications. Most patients maintain IOP control without need for further IOP-lowering surgery. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.