30 research outputs found

    A practical approach for applying Bayesian logic to determine the probabilities of subsurface scenarios: example from an offshore oilfield

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    During appraisal of an undeveloped segment of a producing offshore oilfield, three well penetrations revealed unexpected complexity and compartmentalization. Business decisions on whether and how to develop this segment depended on understanding the possible interpretations of the subsurface. This was achieved using the following steps that incorporated a novel practical application of Bayesian logic. 1. Scenarios were identified to span the full range of possible subsurface interpretations. This was achieved through a facilitated cross-disciplinary exercise including external participants. The exercise generated 12 widely differing subsurface scenarios, which could be grouped into 4 types of mechanisms: slumping, structural, depositional, and diagenetic. 2. Prior probabilities were assigned to each scenario. These probabilities were elicited from the same subsurface team and external experts who performed step 1, using their diverse knowledge and experience. 3. The probabilities of each scenario were updated by evaluating them sequentially with 21 individual pieces of evidence, progressively down-weighting belief in scenarios that were inconsistent with the evidence. For each piece of evidence, the likelihood (chance that the scenario could produce the evidence) was estimated qualitatively by the same team using a “traffic-light” high-medium-low assessment. Offline, these were converted to numerical likelihood values. Posterior probabilities were derived by multiplying the priors by the likelihoods and renormalizing to sum to unity across all of the scenarios. 4. The most probable scenarios were selected for quantitative reservoir modeling, to evaluate the potential outcomes of business decisions, given each scenario. Of the 12 scenarios identified in step 1, most were strongly down-weighted by the sequential revisions against evidence in step 3; after this, only scenarios in the “slumping” group retained significant posterior probabilities. The data showed minimal sensitivity to the initial assumption of prior probability in step 2. This process had several benefits. First, it encouraged the subsurface team to imagine a full range of scenarios that were likely to bracket the actual subsurface “truth,” something that is critical for subsequent decision-making. Second, it allowed belief in the probability of each scenario to be updated systematically in a way that was strongly conditioned to the evidence, so that the choice of scenarios to take through to reservoir modeling was more objective and evidence-based. Third, it allowed an assessment of the usefulness of individual pieces of evidence, which could be used to guide value-of-information assessments for subsequent data acquisition. Finally, the process enabled rigorous Bayesian revision methods to be applied in a simple practical way that engaged the subsurface team without exposing them to the underlying mathematics. During field appraisal and development, when the subsurface is revealed gradually as more data are acquired and studied, the process outlined here provides a practical way of generating and modifying belief in a range of subsurface scenarios while minimizing exposure to potential biases and logical fallacies that could affect subsequent decision quality. It also helps to decide which scenarios are sufficiently probable that they need to be represented by detailed reservoir models

    Próteses parciais fixas reforçadas por fibras: um estudo clínico retrospectivo preliminar

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    The aim of this study was to evaluate the clinical performance (retention rate) of fiber-reinforced composite fixed partial dentures (FPDs). Polyethylene fiber (RibbondÂź) was used combined with restorative composite during FPDs fabrication. FPDs were placed in thirteen patients in a private clinic. Nineteen FPDs were evaluated. The prosthetic space was filled with only one pontic using extracted teeth (2 cases), acrylic resin teeth (11 cases), or with composite resin (6 cases), combined with Polyethylene fiber. The clinical criterion used was based on retention rate of FPDs. If FPDs were in function in the mouth at the time of examination without previous repair they were classified as Complete Survival (CS) restorations. A classification of Survival with Rebonding (SR) was assigned in the event of an adhesive failure, but after rebonding the FPD still remained under evaluation. Treatment was classified as a Failure (F) if the FPD restoration was lost. The time of evaluation was 41.15 months (±15.13). The FPDs evaluated were retained (CS=94.75%), and no failure was found except for in one situation which required rebonding (SR=5.25%). According to the survival estimation method of Kaplan-Meyer the mean survival time was 42.3 months. At the time of evaluation investigated, polyethylene-reinforced FPDs showed a favorable retention rate in preliminary data.O objetivo deste estudo foi avaliar a performance clĂ­nica (percentagem de retenção) de prĂłteses parciais fixas reforçadas por fibras. Fibras de polietileno (RibbondÂź) foram usadas em combinação com resina composta durante a confecção das prĂłteses. Os tratamentos foram realizadas em 13 pacientes, em uma clĂ­nica privada., sendo que 19 prĂłteses foram reavaliadas. O espaço protĂ©tico era preenchido com um pĂŽntico usando o prĂłprio dente extraĂ­do (2 casos), dentes de acrĂ­lico (11 casos) ou confeccionados com resina composta (6 casos), em todas as situaçÔes eram empregadas fibras de polietileno. Os critĂ©rios clĂ­nicos usados foram baseados na percentagem de retenção das prĂłteses parciais fixas. As prĂłteses que estavam em função no momento da avaliação, sem nunca necessitar de qualquer reparo prĂ©vio, foram classificadas como sobrevivĂȘncia completa (SC). A classificação de sobrevivĂȘncia com nova colagem (SR) foi utilizada para os casos de falha adesiva, com posterior cimentação da peça, a qual permanecia em função. O tratamento era classificado como falha (F) quando a restauração era perdida. O tempo mĂ©dio de avaliação foi de 41,15 meses (±15,13). Nenhum caso de falha foi detectado, em apenas um caso houve falha adesiva com posterior colagem da peça (SR=5,25%) e em 94.75% dos casos as prĂłteses permaneciam em função.. De acordo com o mĂ©todo de sobrevida de Kaplan-Meyer o tempo mĂ©dio de sobrevida foi de 42,3 meses. As prĂłteses parciais fixas reforçadas por fibras mostraram uma percentagem de retenção favorĂĄvel neste estudo preliminar

    Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

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    Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified
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