Madison and climate change policy.
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Comment↗
Biomedical subjects
James K Hammitt
Publications and source records attributed to James K Hammitt.
The economic value of fatal and non-fatal occupational risks in Mexico City using actuarial- and perceived-risk estimates.
Compensating wage differentials are used to estimate marginal rates of substitution between income and both fatal and non-fatal occupational-injury risks in the Mexico City metropolitan area. Data are obtained by in-person survey of almost 600 workers and include workers' perceived risks of fatal and non-fatal occupational injury supplemented by actuarial-risk estimates from government statistics. Results using both actuarial- and perceived-risk estimates are reasonably consistent. Estimates of the value per statistical life are between 235,000 US dollars and 325,000 US dollars and estimates of the value per statistical non-fatal injury are between 3500 US dollars and 11,000 US dollars (2002 US dollars). These values are much smaller than corresponding estimates for higher-income countries but are compatible with the small number of prior estimates for lower-income countries.
Actuarial Analysis↗
The influence of geographic location on population exposure to emissions from power plants throughout China.
This analysis seeks to evaluate the influence of emission source location on population exposure in China to fine particles and sulfur dioxide. We use the concept of intake fraction, defined as the fraction of material or its precursor released from a source that is eventually inhaled or ingested by a population. We select 29 power-plant sites throughout China and estimate annual average intake fractions at each site, using identical source characteristics to isolate the influence of geographic location. In addition, we develop regression models to interpret the intake fraction values and allow for extrapolation to other sites. To model the concentration increase due to emissions from selected power plants, we used a detailed long-range atmospheric dispersion model, CALPUFF. Primary fine particles have the highest average intake fraction (1 x 0(-5)), followed by sulfur dioxide (5 x 10(-6)), sulfate from sulfur dioxide (4 x 10(-6)), and nitrate from nitrogen oxides (4 x 10(-6)). For all pollutants, the intake fractions span approximately an order of magnitude across sites. In the regression analysis, the independent variables are meteorological proxies (such as climate region and precipitation) and population at various distances from the source. We find that population terms can explain a substantial percentage of variability in the intake fraction for all pollutants (R(2) between 0.86 and 0.95 across pollutants), with a significant modifying influence of meteorological regime. Near-source population is more important for primary coarse particles while population at medium to long distance is more important for primary fine particles and secondary particles. A significant portion of intake fraction (especially for secondary particles and primary fine particles) occurs beyond 500 km of the source, emphasizing the need for detailed long-range dispersion modeling. These findings demonstrate that intake fractions for power plants in China can be estimated with reasonable precision and summarized using simple regression models. The results should be useful for informing future decisions about power-plant locations and controls.
Air Pollutants↗
Valuation of the risk of SARS in Taiwan.
Two surveys conducted in Taiwan during the spring 2003 severe acute respiratory syndrome (SARS) epidemic reveal a high degree of concern about the threat posed by SARS to Taiwan and its residents, although respondents believe they are knowledgeable about the risk of SARS and that it is susceptible to individual control. Willingness to pay (WTP) to reduce the risk of infection and death from SARS is elicited using contingent valuation methods. Estimated WTP is high, implying values per statistical life of US dollars 3 to 12 million. While consistent with estimates for high-income countries, these values are substantially larger than previous estimates for Taiwan and may be attributable to the high degree of concern about SARS at the time the data were collected.
Adult↗
A benefit-cost analysis of retrofitting diesel vehicles with particulate filters in the Mexico City metropolitan area.
In the Mexico City metropolitan area, poor air quality is a public health concern. Diesel vehicles contribute significantly to the emissions that are most harmful to health. Harmful diesel emissions can be reduced by retrofitting vehicles with one of several technologies, including diesel particulate filters. We quantified the social costs and benefits, including health benefits, of retrofitting diesel vehicles in Mexico City with catalyzed diesel particulate filters, actively regenerating diesel particulate filters, or diesel oxidation catalysts, either immediately or in 2010, when capital costs are expected to be lower. Retrofit with either type of diesel particulate filter or an oxidation catalyst is expected to provide net benefits to society beginning immediately and in 2010. At current prices, retrofit with an oxidation catalyst provides greatest net benefits. However, as capital costs decrease, retrofit with diesel particulate filters is expected to provide greater net benefits. In both scenarios, retrofit of older, dirtier vehicles that circulate only within the city provides greatest benefits, and retrofit with oxidation catalysts provides greater health benefits per dollar spent than retrofit with particulate filters. Uncertainty about the magnitude of net benefits of a retrofit program is significant. Results are most sensitive to values used to calculate benefits, such as the concentration-response coefficient, intake fraction (a measure of exposure), and the monetary value of health benefits.
Air Pollution↗
Precautionary regulation in Europe and the United States: a quantitative comparison.
Much attention has been addressed to the question of whether Europe or the United States adopts a more precautionary stance to the regulation of potential environmental, health, and safety risks. Some commentators suggest that Europe is more risk-averse and precautionary, whereas the United States is seen as more risk-taking and optimistic about the prospects for new technology. Others suggest that the United States is more precautionary because its regulatory process is more legalistic and adversarial, while Europe is more lax and corporatist in its regulations. The flip-flop hypothesis claims that the United States was more precautionary than Europe in the 1970s and early 1980s, and that Europe has become more precautionary since then. We examine the levels and trends in regulation of environmental, health, and safety risks since 1970. Unlike previous research, which has studied only a small set of prominent cases selected nonrandomly, we develop a comprehensive list of almost 3,000 risks and code the relative stringency of regulation in Europe and the United States for each of 100 risks randomly selected from that list for each year from 1970 through 2004. Our results suggest that: (a) averaging over risks, there is no significant difference in relative precaution over the period, (b) weakly consistent with the flip-flop hypothesis, there is some evidence of a modest shift toward greater relative precaution of European regulation since about 1990, although (c) there is a diversity of trends across risks, of which the most common is no change in relative precaution (including cases where Europe and the United States are equally precautionary and where Europe or the United States has been consistently more precautionary). The overall finding is of a mixed and diverse pattern of relative transatlantic precaution over the period.
Journal Article↗
Tiered chemical testing: a value of information approach.
In December 2000 the EPA initiated the Voluntary Children's Chemical Evaluation Program (VCCEP) by asking manufacturers to voluntarily sponsor toxicological testing in a tiered process for 23 chemicals selected for the pilot phase. The tiered nature of the VCCEP pilot program creates the need for clearly defined criteria for determining when information is sufficient to assess the potential risks to children. This raises questions about how to determine the "adequacy" of the existing information and assess the need to undertake efforts to reduce uncertainty (through further testing). This article applies a value of information analysis approach to determine adequacy by modeling how toxicological and exposure data collected through the VCCEP may be used to inform risk management decisions. The analysis demonstrates the importance of information about the exposure level and control costs in making decisions regarding further toxicological testing. This article accounts for the cost of delaying control action and identifies the optimal testing strategy for a constrained decisionmaker who, absent applicable human data, cannot regulate without bioassay data on a specific chemical. It also quantifies the differences in optimal testing strategy for three decision criteria: maximizing societal net benefits, ensuring maximum exposure control while net benefits are positive (i.e., benefits outweigh costs), and controlling to the maximum extent technologically feasible while the lifetime risk of cancer exceeds a specific level of risk. Finally, this article shows the large differences that exist in net benefits between the three criteria for the range of exposure levels where the optimal actions differ.
Animals↗
Economic implications of hormesis.
The implications of hormesis for decision making about control of environmental exposures are examined. From an economic perspective, environmental exposures should be controlled to a level that optimizes health effects and minimizes control costs. The possibility that substances are, or may be, hormetic poses no fundamental challenge for economic analysis. In contrast with the linear no-threshold model, optimal control may be either less or more stringent under the hormetic model, depending on the incremental control cost. When exposure levels or exposure-response functions differ across individuals or are uncertain, the optimal population-level control of exposure must balance possible benefits and harms to individuals against control costs. Economic-incentive-based regulatory instruments, such as tradable permits, are likely to offer less improvement relative to command-and-control regulations under a hormetic model than under a linear no-threshold model.
Cost-Benefit Analysis↗
Cost-effectiveness of treatment for chronic hepatitis C infection in an evolving patient population.
CONTEXT: Approximately 2.7 million US individuals are chronically infected with the hepatitis C virus (HCV). As public health campaigns are pursued, a growing number of treatment candidates are likely to have minimal evidence of liver damage. OBJECTIVE: To examine the clinical benefits and cost-effectiveness of newer treatments for chronic hepatitis C infection in a population of asymptomatic, HCV sero-positive but otherwise healthy individuals. DESIGN AND SETTING: Cost-effectiveness analysis using a Markov model of the natural history of HCV infection and impact of treatment. We used an epidemiologic model to derive a range of natural history parameters that were empirically calibrated to provide a good fit to observed data on both prevalence of HCV seropositivity and time trends in outcomes related to HCV infection. PATIENTS: Cohorts of 40-year-old men and women with elevated levels of alanine aminotransferase, positive results on quantitative HCV RNA assays and serologic tests for antibody to HCV, and no histological evidence of fibrosis on liver biopsy. INTERVENTIONS: Monotherapy with standard or pegylated interferon alfa-2b; combination therapy with standard or pegylated interferon plus ribavirin. MAIN OUTCOME MEASURES: Lifetime costs, life expectancy, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios. RESULTS: The probability of patients with chronic HCV developing cirrhosis over a 30-year period ranged from 13% to 46% for men and from 1% to 29% for women. The incremental cost-effectiveness of combination therapy with pegylated interferon for men ranged from 26 000 dollars to 64 000 dollars per QALY for genotype 1 and from 10 000 dollars to 28 000 dollars per QALY for other genotypes; and for women ranged from 32 000 dollars to 90 000 dollars for genotype 1 and from 12 000 dollars to 42 000 dollars for other genotypes. Because the benefits of treatment were realized largely in the form of improvements in health-related quality of life, rather than prolonged survivorship, cost-effectiveness ratios expressed as dollars per year of life were substantially higher. Results were most sensitive to assumptions about the gains and decrements in health-related quality of life associated with treatment. CONCLUSIONS: While newer treatment options for hepatitis C appear to be reasonably cost-effective on average, these results vary widely across different patient subgroups and depend critically on quality-of-life assumptions. As the pool of persons eligible for treatment for HCV infection expands to the more general population, it will be imperative for patients and their physicians to consider these assumptions in making individual-level treatment decisions.
Adult↗
Fuels for urban transit buses: a cost-effectiveness analysis.
Public transit agencies have begun to adopt alternative propulsion technologies to reduce urban transit bus emissions associated with conventional diesel (CD) engines. Among the most popular alternatives are emission controlled diesel buses (ECD), defined here to be buses with continuously regenerating diesel particle filters burning low-sulfur diesel fuel, and buses burning compressed natural gas (CNG). This study uses a series of simplifying assumptions to arrive at first-order estimates for the incremental cost-effectiveness (CE) of ECD and CNG relative to CD. The CE ratio numerator reflects acquisition and operating costs. The denominator reflects health losses (mortality and morbidity) due to primary particulate matter (PM), secondary PM, and ozone exposure, measured as quality adjusted life years (QALYs). We find that CNG provides larger health benefits than does ECD (nine vs six QALYs annually per 1000 buses) but that ECD is more cost-effective than CNG (dollar 270 000 per QALY for ECD vs dollar 1.7 million to dollar 2.4 million for CNG). These estimates are subject to much uncertainty. We identify assumptions that contribute most to this uncertainty and propose potential research directions to refine our estimates.
Air Pollutants↗
Use of expert judgment in exposure assessment: part 2. Calibration of expert judgments about personal exposures to benzene.
The recent movement of regulatory agencies toward probabilistic analyses of human health and environmental risks has focused greater attention on the quality of the estimates of variability and uncertainty that underlie them. Of particular concern is how uncertainty--a measure of what is not known--is characterized, as uncertainty can play an influential role in analyses of the need for regulatory controls or in estimates of the economic value of additional research. This paper reports the second phase of a study, conducted as an element of the National Human Exposure Assessment Survey (NHEXAS), to obtain and calibrate exposure assessment experts judgments about uncertainty in residential ambient, residential indoor, and personal air benzene concentrations experienced by the nonsmoking, nonoccupationally exposed population in U.S. EPA's Region V. Subjective judgments (i.e., the median, interquartile range, and 90% confidence interval) about the means and 90th percentiles of each of the benzene distributions were elicited from the seven experts participating in the study. The calibration or quality of the experts' judgments was assessed by comparing them to the actual measurements from the NHEXAS Region V study using graphical techniques, a quadratic scoring rule, and surprise and interquartile indices. The results from both quantitative scoring methods suggested that, considered collectively, the experts' judgments were relatively well calibrated although on balance, underconfident. The calibration of individual expert judgments appeared variable, highlighting potential pitfalls in reliance on individual experts. In a surprising finding, the experts' judgments about the 90th percentiles of the benzene distributions were better calibrated than their predictions about the means; the experts tended to be overconfident in their ability to predict the means. This paper is also one of the first calibration studies to demonstrate the importance of taking into account intraexpert correlation on the statistical significance of the findings. When the judgments were assumed to be independent, analysis of the surprise and interquartile indices found evidence of poor calibration (P<0.05). However, when the intraexpert correlation in the study was taken into account, these findings were no longer statistically significant. The analysis further found that the experts' judgments scored better than estimates of Region V benzene concentrations simply drawn from earlier studies of ambient, indoor and personal benzene levels in other U.S. cities. These results suggest the value of careful elicitation of expert judgments in characterizing exposures in probabilistic form. Additional calibration studies need to be undertaken to corroborate and extend these findings.
Air Pollution, Indoor↗
Safety impacts of SUVs, vans, and pickup trucks in two-vehicle crashes.
Policy makers, vehicle manufacturers, and consumers have shown growing concern about the relative safety of sport utility vehicles (SUVs), vans, pickups, and cars. Empirical analysis of real-world crashes is complicated by the possibility that apparent relationships between vehicle type and safety may be confounded by other factors, such as driver behavior and crash circumstances. This study compares different vehicle types with respect to their crashworthiness (self-protection) and aggressivity (risk to others) in crashes between two passenger vehicles. The U.S. Crashworthiness Data System is used to analyze detailed information on 6,481 drivers involved in crashes during 1993-1999. Logistic regression analysis is used to model the risk of serious injury or death to a driver, conditional on a crash occurring. Covariates include the body type of each vehicle in the crash; the driver's age, gender, and restraint use; and the configuration of the crash. A unique feature of this study is the use of "delta-v" to represent the joint effects of vehicle mass and crash severity. While estimated effects are somewhat sensitive to the injury severity level used as the outcome variable, SUVs, vans, and pickups appear to be more aggressive and may be more crashworthy than cars. Effects of pickups are most pronounced. Drivers in pickups face less risk of serious injury than car drivers (odds ratio [OR], 0.35; 95% confidence interval [CI], 0.20-0.60), and drivers who collide with pickups experience more than twice the risk than those who collide with a car (OR, 2.18; 95% CI, 1.03-4.62). While vehicle mass and crash severity contribute to the apparent crashworthiness and aggressivity of passenger vehicles, other vehicle characteristics associated with body type (e.g., the stiffness and height of the underlying structure of the vehicle) also influence safety risks.
Journal Article↗
Empirically calibrated model of hepatitis C virus infection in the United States.
This study presents a comprehensive epidemiologic model of hepatitis C in the United States. Through empirical calibration of model parameter values, the objectives were to gain insights into uncertain aspects of the natural history of hepatitis C and to improve the basis for projecting the future course of the epidemic. A systematic review of the published literature was conducted to define plausible ranges around model parameters, and multiple simulations of the model were undertaken using sampled values from these ranges. Model predictions produced by each set of sampled values were compared with available epidemiologic data on infection prevalence and mortality from liver cancer, and various goodness-of-fit criteria were used to identify the range of parameter values that were consistent with these data. The results of the study indicate that rates of progression to advanced liver disease may be lower than previously assumed. The authors also found that a wide range of plausible assumptions about heterogeneity in these rates, beyond that explained by age and sex, is consistent with observed epidemiologic trends. These findings have important implications both for individual clinical decisions and for broader public health policy.
Adult↗
Timing of prophylactic surgery in prevention of diverticulitis recurrence: a cost-effectiveness analysis.
Although surgery is recommended after two or more attacks of uncomplicated diverticulitis, the optimal timing for surgery in terms of cost-effectiveness is unknown. A Markov model was used to compare the costs and outcomes of performing surgery after one, two, or three uncomplicated attacks in 60-year-old hypothetical cohorts. Transition state probabilities were assigned values using published data and expert opinion. Costs were estimated from Medicare reimbursement rates. Surgery after the third attack is cost saving, yielding more years of life and quality adjusted life years at a lower cost than the other two strategies. The results were not sensitive to many of the variables tested in the model or to changes made in the discount rate (0-5%). In conclusion, performing prophylactic resection after the third attack of diverticulitis is cost saving in comparison to resection performed after the first or second attacks and remains cost-effective during sensitivity analysis.
Cohort Studies↗
Tools for comparative analysis of alternatives: competing or complementary perspectives?
A third generation of environmental policy making and risk management will increasingly impose environmental measures, which may give rise to analyzing countervailing risks. Therefore, a comprehensive analysis of all risks associated with the decision alternatives will aid decision-makers in prioritizing alternatives that effectively reduce both target and countervailing risks. Starting with the metaphor of the ripples caused by a stone that is thrown into a pond, we identify 10 types of ripples that symbolize, in our case, risks that deserve closer examination: direct, upstream, downstream, accidental risks, occupational risks, risks due to offsetting behavior, change in disposable income, macro-economic changes, depletion of natural resources, and risks to the manmade environment. Tools to analyze these risks were developed independently and recently have been applied to overlapping fields of application. This suggests that either the tools should be linked in a unified framework for comparative analysis or that the appropriate field of application for single tools should be better understood. The goals of this article are to create a better foundation for the understanding of the nature and coverage of available tools and to identify the remaining gaps. None of the tools is designed to deal with all 10 types of risk. Provided data suggest that, of the 10 types of identified risks, those associated with changes in disposable income may be particularly significant when decision alternatives differ with respect to their effects on disposable income. Finally, the present analysis was limited to analytical questions and did not capture the important role of the decision-making process itself.
Cost-Benefit Analysis↗
Selecting human health metrics for environmental decision-support tools.
Environmental decision-support tools often predict a multitude of different human health effects due to environmental stressors. The accounting and aggregating of these morbidity and mortality outcomes is key to support decision making and can be accomplished by different methods that we call human health metrics. This article attempts to answer two questions: Does it matter which metric is chosen? and What are the relevant characteristics of these metrics in environmental applications? Three metrics (quality adjusted life years (QALYs), disability adjusted life years (DALYs), and willingness to pay (WTP)) have been applied to the same diverse set of health effects due to environmental impacts. In this example, the choice of metric mattered for the ranking of these environmental impacts and it was found for this example that WTP was dominated by mortality outcomes. Further, QALYs and DALYs are sensitive to mild illnesses that affect large numbers of people and the severity of these mild illnesses are difficult to assess. Eight guiding questions are provided in order to help select human health metrics for environmental decision-support tools. Since health metrics tend to follow the paradigm of utility maximization, these metrics may be supplemented with a semi-quantitative discussion of distributional and ethical aspects. Finally, the magnitude of age-dependent disutility due to mortality for both monetary and nonmonetary metrics may bear the largest practical relevance for future research.
Biometry↗
Assessing preferences for prevention versus treatment using willingness to pay.
BACKGROUND: Rising health care costs and limited resources necessitate trade-offs between resources allocated toward prevention and those toward treatment. Information from opinion polls suggests citizens favor spending a higher proportion of all health care dollars on prevention rather than treatment. OBJECTIVES: To assess the policy implications of willingness to pay (WTP) for use in cost-benefit analysis (CBA) as a method for capturing individual preferences for prevention and treatment in the context of resource allocation decisions. METHODS: The authors recruited a random sample of 1456 US residents age 18 years and greater by telephone using random-digit dialing. The survey was designed as a 3-stage (phone-mail-phone) process and was conducted between December 1998 and March 1999. For all persons completing the survey (N = 1104), the authors 1st collected respondents' opinions about the costs and effectiveness of prevention versus treatment programs in general. Half of respondents were then asked to state their WTP for a hypothetical prevention scenario and half were asked to state their WTP for a hypothetical treatment scenario. Both scenarios were specific to the same health context and included an identical reduction in mortality risk. RESULTS: WTP for treatment was significantly greater than WTP for prevention, $665 and $223, respectively. Prior opinions on the relative effectiveness afforded by preventive and treatment interventions moderately influenced the WTP estimates for persons randomized to either scenario. Prior opinions on costs had no significant effect on WTP estimates for either scenario. WTP significantly increased with age and household income in the full sample but was not significantly affected by gender or educational attainment. CONCLUSIONS: The aggregated WTP responses from the prevention and treatment scenarios presented in our study would imply that treatment is more strongly preferred by society than prevention when the health context is the same and benefits of each are held constant. A better understanding is needed of the discrepancy between citizens' stated preferences for prevention (e.g., through polling) and our findings that they were willing to pay substantially more for treatment than for prevention.
Adult↗