Susie ElSaadany

On the performance of social network and likelihood-based expert weighting schemes

Using expert judgment data from the TU Delfts expert judgment database, we compare the performance of different weighting schemes, namely equal weighting, performance-based weighting from the classical model [Cooke RM. Experts in uncertainty. Oxford: Oxford University Press; 1991.], social network (SN) weighting and likelihood weighting. The picture that emerges with regard to SN weights is rather mixed. SN theory does not provide an alternative to performance-based combination of expert judgments, since the statistical accuracy of the SN decision maker is sometimes unacceptably low. On the other hand, it does outperform equal weighting in the majority of cases. The results here, though not overwhelmingly positive, do nonetheless motivate further research into social interaction methods for nominating and weighting experts. Indeed, a full expert judgment study with performance measurement requires an investment in time and effort, with a view to securing external validation. If high confidence in a comparable level of validation can be obtained by less intensive methods, this would be very welcome, and would facilitate the application of structured expert judgment in situations where the resources for a full study are not available. Likelihood weights are just as resource intensive as performance-based weights, and the evidence presented here suggests that they are inferior to performance-based weights with regard to those scoring variables which are optimized in performance weights (calibration and information). Perhaps surprisingly, they are also inferior with regard to likelihood. Their use is further discouraged by the fact that they constitute a strongly improper scoring rule.

Expert Elicitation for the Judgment of Prion Disease Risk Uncertainties

There is a high level of uncertainty surrounding the potential for iatrogenic prion transmission through transplantation, medical instrument reuse, blood transfusion, and blood product use due to a lack of evidence-based research on this important risk issue. A group of specialists was enlisted to evaluate some of the knowledge gaps in this area using the “Classical Model,” a structured elicitation procedure for weighting and pooling expert judgment. The elicitation exercise was undertaken in March 2009 with 11 transmissible spongiform encephalopathy (TSE) experts who were first calibrated using a series of seed questions for which the answers are known; they were then asked to answer a number of target questions that are important for risk assessment purposes, but for which there remains high uncertainty at this time. The target questions focused on variant Creutzfeldt–Jakob disease (vCJD) prevalence, incubation times for vCJD, genetic susceptibility to prion disease, blood infectivity, prion reduction of blood and blood products, surgical instrument risks, and interspecies transmission of TSEs. The experts were also asked to perform pairwise risk rankings for 12 different potential routes of infection. Dura mater transplantation was seen as having the highest risk, while dental tissue grafts were viewed as presenting the lowest risk of iatrogenic transmission. The structured elicitation procedure provides a rational, auditable, and repeatable basis for obtaining useful information on prion disease risk issues, for which data are sparse.

Documenting a transfusion: how well is it done?

BACKGROUND: Current practice in transfusion medicine promotes clear documentation of transfusion‐related events including the fact that the patient has been informed of the related risks and benefits.

Expert judgement and re-elicitation for prion disease risk uncertainties.

Much uncertainty surrounds transmission of transmissible spongiform encephalopathies (TSEs) through blood and blood derived products. A first expert elicitation with 14 experts was conducted in March 2008, and a second re-elicitation involving 11 experts was held a year later in March 2009. Both expert groups were calibrated using a series of seed questions for which values are known, and then were asked to provide their individual judgements on a set of seven target questions for which values are not known or have not been determined through conventional research. Questions dealing with uncertainty of TSE prevalence, genotype effects, susceptibility, and infectivity were answered by the experts. Elicitation can be used to obtain quantitative values for parameters affecting prion uncertainty gaps. We show that the method is amenable to re-elicitation over time allowing refinement of expert opinion as new knowledge becomes available for improved risk assessments where data gaps continue to exist.

The risk to human islet cell transplant recipients of acquiring variant Creutzfeldt-Jakob disease: a provisional quantitative risk assessment.

different soluble (HLA-G5–HLA-G7) and membrane bound (HLA-G1–HLA-G4) isoforms may be involved in regulation of accommodation of different allograft types. Recently, only HLA-G1 isoform in peripheral blood mononuclear cells and biopsy samples was reported to have association with kidney allograft state (10). In summary, our results suggest that, unlike in liver transplantpediatricrecipients, serological monitoring for HLA-G levels in pediatric kidney transplant recipients may have limited benefit and poor correlation with the underlying phenotype of transplant injury, at least early after transplantation. Further studies should be targeted at serial analysis of soluble and membrane-bound HLA-G molecules later after transplantation to assess whether undulating levels of serum HLA-G can provide some direction for causality for the immunologically diverse outcomes after pediatric kidney transplantation and to evaluate and investigate the specific regulatory properties of HLA-G in organ transplantation.

Epidemiological Study of Creutzfeldt-Jakob Disease Death Certificates in Canada, 1979–2001

Introduction: A descriptive epidemiological analysis to update trends of Creutzfeldt-Jakob disease (CJD) deaths, from 1979–2001, was undertaken. Methods: Cases with CJD as underlying cause were extracted. Age-adjusted death rates by age, sex, and province were calculated. Information on birthplace, autopsy indications and type of work were examined for death certificates from 1979 to 1997. Results: 462 cases were identified between 1979 and 1997. The average annual age-standardized mortality rate was 0.93 deaths per million persons during this period and 1.03 for 1998–2001. Persons 60 years or older demonstrated the highest average annual mortality rate. Rates were slightly higher among males and increased with age. Persons born in Canada accounted for 72% of deaths. Cause of death was verified by autopsy for 9.1% of patients while 21% of deaths indicated that additional information relating to underlying cause was expected. The service industry occupation represented the largest mortality (Quebec does not capture these data). Conclusions: Canadian rates are consistent with those of the United States and slightly higher than those of certain European countries. Approximately 44% of CJD cases had an autopsy record, though many were incomplete. We are unable to determine a relation with occupation. We recommend annual analysis of CJD death registrations for updated surveillance of trends, as mortality data are an efficient tool for monitoring incidence.

The Risk of Blood-Borne Viral Infection due to Syringe Re-Use

In the fall of 2008, light was shed on the practice of syringe re-use occurring in western Canada (Government of Alberta, 2009). In this situation, syringes had been re-used between patients to administer sedating medication through patient intravenous (IV) lines (Government of Alberta, 2009). Later it was reported that other incidents of syringe re-use had occurred in Canada (CBC News-Edmonton, 2008a;CBC News-Edmonton, 2008b). The question arose of whether this practice may have resulted in the transmission of bloodborne pathogens to patients and, if so, how many and with what level of risk. To answer this question, a retrospective study involving approximately 1,400 patients was undertaken (Government of Alberta, 2009). However, questions were also raised as to whether estimates based on modeling scenarios could provide information to guide decisions on the need for look-backs.

Expert elicitation on the uncertainties associated with chronic wasting disease

ABSTRACT A high degree of uncertainty exists for chronic wasting disease (CWD) transmission factors in farmed and wild cervids. Evaluating the factors is important as it helps to inform future risk management strategies. Expert opinion is often used to assist decision making in a number of health, science, and technology domains where data may be sparse or missing. Using the “Classical Model” of elicitation, a group of experts was asked to estimate the most likely values for several risk factors affecting CWD transmission. The formalized expert elicitation helped structure the issues and hence provide a rational basis for estimating some transmission risk factors for which evidence is lacking. Considered judgments regarding environmental transmission, latency of CWD transmission, management, and species barrier were provided by the experts. Uncertainties for many items were determined to be large, highlighting areas requiring more research. The elicited values may be used as surrogate values until research evidence becomes available.

Enhanced surveillance for measles in low-incidence territories of the Russian Federation: defining a rate for suspected case investigation.

The rate of case investigation for measles-like illness (MLI) is an important indicator for the quality of measles surveillance in countries targeting measles elimination. However, a benchmark rate is still being discussed. We assessed different rates of investigation in 11 territories of the Russian Federation with low reported measles incidence during the previous 4-7 years. Each territory maintained their existing surveillance activities and also undertook additional surveillance activities for MLI over a 3-year period. The annual routine rate of investigation varied from 0·06 to 1·8/100,000 population; the overall rate of investigation, including enhanced surveillance, varied from 1·4 to 7·2/100,000. Forty-nine (30·8%) of 159 measles cases detected were identified through enhanced surveillance. Based on the results of this study, the Russian Federation concluded that a rate of routine investigation of 2/100,000 provided the best balance between available resources and sensitivity for detection of measles cases.

Mathematical Models for Estimating the Risks of Bovine Spongiform Encephalopathy (BSE).

When the bovine spongiform encephalopathy (BSE) epidemic first emerged in the United Kingdom in the mid 1980s, the etiology of animal prion diseases was largely unknown. Risk management efforts to control the disease were also subject to uncertainties regarding the extent of BSE infections and future course of the epidemic. As understanding of BSE increased, mathematical models were developed to estimate risk of BSE infection and to predict reductions in risk in response to BSE control measures. Risk models of BSE-transmission dynamics determined disease persistence in cattle herds and relative infectivity of cattle prior to onset of clinical disease. These BSE models helped in understanding key epidemiological features of BSE transmission and dynamics, such as incubation period distribution and age-dependent infection susceptibility to infection with the BSE agent. This review summarizes different mathematical models and methods that have been used to estimate risk of BSE, and discusses how such risk projection models have informed risk assessment and management of BSE. This review also provides some general insights on how mathematical models of the type discussed here may be used to estimate risks of emerging zoonotic diseases when biological data on transmission of the etiological agent are limited.