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Biomedical subjects

M C Weinstein

Publications and source records attributed to M C Weinstein.

155 records · Page 9Linked to original sources
PubMedDate not supplied

Whose blood is safer? The effect of the stage of the epidemic on screening for HIV.

BACKGROUND: With improvements in HIV antibody test (ELISA) performance, the window of time between infection and seroconversion becomes a major source of error in HIV screening. The authors examined its impact on the false-reassurance rate (FRR). METHODS: Test sensitivity was modeled as the product of two factors: the inherent sensitivity (sensitivity when antibody is present) and the probability that antibody is present in infected blood. A model of HIV and AIDS incidence was used to derive an estimate of the probability of remaining in the seronegative window (pw) among those who are infected. With plausible assumptions, this probability approaches 0.03. The FRR was then estimated as a function of the probability of remaining in the seronegative window, the prevalence of HIV, and the inherent sensitivity of the ELISA test were estimated. RESULTS: The FRRs for two blood donor groups, one with an HIV prevalence of 0.004 and a typical probability of remaining in the seronegative window (pw = 0.03) and the other with a higher prevalence of 0.017 but fewer donors in the window (pw = 0.003), are equal (140 per million donors) if the blood is negative on a single ELISA test. After two negative tests or a single test that can detect antibody more reliably, however, the FRR is much higher in the group with the higher pw (= 120 per million compared with 50 per million), because the greater numbers of donors in the window more than offsets the lower prevalence. CONCLUSION: With improvements in inherent sensitivity of ELISA by virtue of technical progress or retesting, the prevalence of HIV infection may no longer play the critical role in degrading the results of blood screening. As inherent test performance improves, tests are increasingly likely to miss infected blood because of the seronegative-window error rather than because of measurement error. Window error plays a proportionally greater role during the early stages of HIV dissemination in a population where the incidence of new HIV infection is high relative to the incidence of AIDS. These findings may explain, in part, the recent observation that cases of transfusion of contaminated blood often take place in areas where AIDS epidemics have started recently. They also suggest that the traditional strategy of soliciting blood donors from low-prevalence populations may not always be optimal, unless such populations are truly low-risk.

Blood Banks↗
PubMedDate not supplied

Decision and cost-utility analyses of surgical versus transcatheter closure of patent ductus arteriosus: should you let a smile be your umbrella?

Decision and cost-utility analyses considered the tradeoffs of treating patent ductus arteriosus (PDA) using conventional surgery versus transcatheter implantation of the Rashkind occluder. Physicians and informed lay parents assigned utility scores to procedure success/complications combinations seen in prognostically similar pediatric patients with isolated PDA treated from 1982 to 1987. Utility scores multiplied by outcome frequencies from a comparative study generated expected utility values for the two approaches. Cost-utility analyses combined these results with simulated provider cost estimates from 1989. On a 0-100 scale (worst to best observed outcome), the median expected utility for surgery was 99.96, versus 98.88 for the occluder. Results of most sensitivity analyses also slightly favored surgery. Expected utility differences based on 1987 data were minimal. With a mean overall simulated cost of $8,838 vs $12,466 for the occluder, surgery was favored in most cost-utility analyses. Use of the inherently less invasive but less successful, more risky, and more costly occluder approach conferred no apparent net advantage in this study. Analyses of comparable current data would be informative.

Angioplasty↗
PubMedDate not supplied

Predicting mortality after coronary artery bypass surgery: what do artificial neural networks learn? The Steering Committee of the Cardiac Care Network of Ontario.

OBJECTIVE: To compare the abilities of artificial neural network and logistic regression models to predict the risk of in-hospital mortality after coronary artery bypass graft (CABG) surgery. METHODS: Neural network and logistic regression models were developed using a training set of 4,782 patients undergoing CABG surgery in Ontario, Canada, in 1991, and they were validated in two test sets of 5,309 and 5,517 patients having CABG surgery in 1992 and 1993, respectively. RESULTS: The probabilities predicted from a fully trained neural network were similar to those of a "saturated" regression model, with both models detecting all possible interactions in the training set and validating poorly in the two test sets. A second neural network was developed by cross-validating a network against a new set of data and terminating network training early to create a more generalizable model. A simple "main effects" regression model without any interaction terms was also developed. Both of these models validated well, with areas under the receiver operating characteristic curves of 0.78 and 0.77 (p > 0.10) in the 1993 test set. The predictions from the two models were very highly correlated (r=0.95). CONCLUSIONS: Artificial neural networks and logistic regression models learn similar relationships between patient characteristics and mortality after CABG surgery.

Aged↗
PubMedDate not supplied

A Monte Carlo simulation of advanced HIV disease: application to prevention of CMV infection.

BACKGROUND: Disagreement exists among decision makers regarding the allocation of limited HIV patient care resources and, specifically, the comparative value of preventing opportunistic infections in late-stage disease. METHODS: A Monte Carlo simulation framework was used to evaluate a state-transition model of the natural history of HIV illness in patients with CD4 counts below 300/mm3 and to project the costs and consequences of alternative strategies for preventing AIDS-related complications. The authors describe the model and demonstrate how it may be employed to assess the cost-effectiveness of oral ganciclovir for prevention of cytomegalovirus (CMV) infection. RESULTS: Ganciclovir prophylaxis confers an estimated additional 0.7 quality-adjusted month of life at a net cost of $10,700, implying an incremental cost-effectiveness ratio of roughly $173,000 per quality-adjusted life year gained. Sensitivity analysis reveals that this baseline result is stable over a wide range of input data estimates, including quality of life and drug efficacy, but it is sensitive to CMV incidence and drug price assumptions. CONCLUSIONS: The Monte Carlo simulation framework offers decision makers a powerful and flexible tool for evaluating choices in the realm of chronic disease patient care. The authors have used it to assess HIV-related treatment options and continue to refine it to reflect advances in defining the pathogenesis and treatment of AIDS. Compared with alternative interventions, CMV prophylaxis does not appear to be a cost-effective use of scarce HIV clinical care funds. However, targeted prevention in patients identified to be at higher risk for CMV-related disease may warrant consideration.

AIDS-Related Opportunistic Infections↗
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Uncertainty in decision models analyzing cost-effectiveness: the joint distribution of incremental costs and effectiveness evaluated with a nonparametric bootstrap method.

PURPOSE: To illustrate the use of a nonparametric bootstrap method in the evaluation of uncertainty in decision models analyzing cost-effectiveness. METHODS: The authors reevaluated a previously published cost-effectiveness analysis that used a Markov model comparing initial percutaneous transluminal angioplasty with bypass surgery for femoropopliteal lesions. Each probability in the model was simulated with a first-order Monte Carlo simulation to represent sampling uncertainty. Superimposed on this, a second-order Monte Carlo simulation was performed to represent parameter uncertainty, drawing the probability values from nonparametric distributions based on published data or from primary collected data as available. After simulation of a mixed (i.e., non-identical) cohort of 30,000 patients, 3,000 bootstrap samples of 1,000 patients each were drawn and the joint distribution of mean incremental costs and mean effectiveness gained was evaluated. RESULTS: Using a bootstrap sample size of 1,000 patients, 92.7% of the joint distribution of mean incremental costs and mean effectiveness gained fell in the quadrant where angioplasty dominated bypass surgery. Another 6.9% of samples demonstrated either greater effectiveness with an incremental cost-effectiveness ratio of at most $20,000/QALY gained, or cost savings with a ratio of at least $20,000 saved/QALY lost. CONCLUSION: A nonparametric bootstrap method can be used to estimate the joint distribution of mean incremental costs and mean effectiveness gained, and the results can provide an understanding of the uncertainty in a cost-effectiveness analysis based on a decision model.

Angioplasty, Balloon↗
PubMedDate not supplied

Estimating general-population utilities using one binary-gamble question per respondent.

This study used a single binary-gamble question per health state per respondent to obtain societal preferences for the health states intermittent claudication and major amputation and compare those with Health Utilities Indices obtained from patients, to test the feasibility of this method, and to investigate whether the utility depends on the presentation of a vignette as generic vs disease-specific. A random sample of the general U.S. population (n = 1,003) was randomly divided into ten subgroups. In telephone interviews, subjects answered one binary-gamble question in a standard-gamble format for each of two health states. The risks of death varied across subgroups but not between health states. Mean utility was estimated by the area above the proportional distribution of responses indicating acceptance of the gamble. The method is based on the binary-choice method used in contingent-valuation studies of willingness to pay. The health states were alternatively described by generic and disease-specific vignettes in two subsamples. The results suggest that the binary-gamble question can be used to obtain societal preferences for health states, and that disease-specific descriptions yield lower utilities compared with generic descriptions of health states.

Adult↗
PubMedDate not supplied

Cost-effectiveness of regulations against using a cellular telephone while driving.

PURPOSE: To evaluate the cost-effectiveness of regulations that prohibit using a cellular telephone while driving a motor vehicle. DESIGN: Decision analysis of risks and benefits related to cellular telephones and driving. SETTING: United States population in 1997. MEASURES: Health benefits measured as the quality-adjusted life years potentially saved. Financial benefits measured as health care and other services potentially averted. Costs of regulation measured as the lost productivity derived from willingness to pay for cellular telephone calls. RESULTS: Under base-case conditions, cellular telephone calls in the United States each day accounted for about 984 reported collisions, 1,729 total collisions, 2 deaths, 317 persons with injuries, 99 lost years of life expectancy, 161 lost quality-adjusted life years, $1 million in health care costs, and $4 million in property damage and other costs. This reflected a total of about 35 million telephone calls while driving, 70 million calling minutes, and $33 million in total value to society. The estimated cost-effectiveness ratio for a regulation restricting cellular telephone usage while driving was $300,000 per quality-adjusted life year saved, but ranged from $50,000 to $700,000 under alternative assumptions and interpretations of data. Regulations applied to teenage males could be cost-saving to society if the value of a call fell below 37 cents per minute. CONCLUSIONS: Regulations restricting cellular telephone usage while driving are less cost-effective for society than other safety measures. Nevertheless, regulations may be justifiable because the benefits and harms do not always involve the individual who has the cellular telephone. Increasing the price of a call (or adding a supplementary tax) might decrease the number of discretionary calls, be cost-saving for society, and be life-saving for individuals.

Accidents, Traffic↗
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The FDA's regulation of health economic information.

Section 114 of the Food and Drug Administration Modernization Act of 1997 was intended to increase the flow of health economic information from pharmaceutical manufacturers to managed care decisionmakers. But the legislation raises a host of complex questions and has provoked diverse opinions from inside and outside the pharmaceutical industry. Moreover, the Food and Drug Administration (FDA) has yet to issue interpretative guidance on the subject. The challenge in implementing Section 114 lies in developing a policy that improves health economic information exchange while protecting consumers from misleading claims and preserving incentives for manufacturers to conduct rigorous studies.

Drug Industry↗