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An evaluation of the environmental and health effects of vehicle exhaust catalysts in the UK |
Hutchinson E J, Pearson P J |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The use of vehicle exhaust catalysts (VECs) was investigated.
Study population The study population comprised all urban residents in Great Britain.
Setting The study setting was the community. The economic study was carried out in London, UK.
Dates to which data relate The effectiveness data were derived from studies and reports published between 1991 and 2002. The price year was 1998.
Source of effectiveness data The effectiveness data were derived from a variety of sources, including surveys, national statistics, epidemiological surveys, personal communication with experts and the authors' assumptions.
Modelling A health risk assessment model was conducted to carry out two evaluations using 1992 as the base-case. First, an ex-post evaluation of the health effects arising from the action of VECs on pollutant levels in urban areas from 1993 to 1998 was conducted. Second, an ex-ante evaluation of the health benefits projected to 2005, since full catalyst penetration in the car fleet was expected by this year, was carried out. The model consisted of four steps.
Step 1, the authors estimated reductions in emissions of oxides of nitrogen (NOx), volatile organic compounds (VOCs), carbon monoxide and particulate matter "<10 microg" in diameter (PM10) arising from the use of VECs.
Step 2, the authors estimated the resulting changes in ambient urban concentrations for the primary pollutants carbon monoxide, VOCs and primary PM10, and for the secondary pollutants nitrogen dioxide (NO2), ozone (O3) and secondary PM10.
Step 3, the authors quantified the health benefits, in terms of the morbidity and mortality, arising from these changes in pollution.
Step 4, a cost-benefit analysis was carried out.
Outcomes assessed in the review The outcomes assessed in the review were:
the contribution of gasoline automobiles to urban emissions;
the percentage reduction in total urban emissions due to catalysts;
the ambient urban concentrations of pollutants PM10, O3 and NO2;
the exposure-response functions to assess the health benefits arising from changes in pollutant concentrations in terms of the effects on morbidity and mortality;
the mortality rate in Great Britain; and
the total number of hospital admissions by diagnosis.
Study designs and other criteria for inclusion in the review The authors reported that exposure-response functions were selected from epidemiological studies. These epidemiological studies were selected from reviews and meta-analyses.
Sources searched to identify primary studies Criteria used to ensure the validity of primary studies To e included in the review, epidemiological studies had to meet certain criteria. Such inclusion criteria were consistency with findings from other studies, quality of exposure data for the relevant period, statistical precision of the risk estimates, inclusion of data on exposure-response relationships, and inclusion of data on major confounding factors. All selected studies controlled for season and the effect of co-pollutants. Where possible, studies conducted in European cities were used.
Methods used to judge relevance and validity, and for extracting data The validity of the primary studies does not appear to have been assessed.
Number of primary studies included Over 40 primary studies were included in the review.
Methods of combining primary studies Overall, the method used to combine the primary studies was not reported. The authors reported that available reviews and meta-analyses from the USA were explored and used to produce an upper-bound estimate of health effects.
Investigation of differences between primary studies Results of the review The urban population in the UK in 1993 was 47,849,255 people.
The mortality rate in 1992 in the UK was 1,098.19 per 100,000 population.
The rate of respiratory hospital admissions per 100,000 population was 1,245.83 in 1992 to 1993. In 1992, the rate per 100,000 population of emergency respiratory hospital admissions was 770.
In 1992, the average ambient urban concentration of pollutants was 26.6 microg/m3 PM10, 15.28 ppb O3 and 29.58 ppb NO2.
For 1993 to 1998, the average reduction in pollutants was 0.92 microg/m3 PM10, -0.46 ppb O3 and 2.45 ppb NO2.
For 1993 to 2005, the average reduction in pollutants was 2.24 microg/m3 PM10, -1.04 ppb O3 and 5.59 ppb NO2.
The exposure response function for mortality was 0.074 (95% confidence interval, CI: 0.044 to 0.075) for PM10 and 0.106 (95% CI: 0.051 to 0.153) for O3.
The exposure response function for morbidity (i.e. hospital admissions) was 0.08 (95% CI: 0.045 to 0.11) for PM10, 0.137 (95% CI: 0.061 to 0.210) for O3 and 0.096 (95% CI: 0.008 to 0.187) for NO2.
Methods used to derive estimates of effectiveness The effectiveness data from the review were supplemented with personal communications with experts and the authors' assumptions.
Estimates of effectiveness and key assumptions The authors assumed the following:
lead emissions from catalyst-equipped cars were zero because of the use of unleaded fuel;
between 1993 and 2005 all emissions (other than PM10, O3 and NO2) would remain constant; and
there was a direct relationships between emissions reductions and reductions in concentrations.
Measure of benefits used in the economic analysis Monetary benefits were used as the measure of benefit. Economic valuations were applied to the estimated changes in respiratory hospital admissions and mortality. Valuations of respiratory hospital admissions incorporated values for pain, suffering and a lost time component associated with an increase in risk for hospital admissions. Relevant willingness-to-pay valuations to avoid one hospital admission were selected from an array of recent contingent valuation methods. Values for changes in mortality due to changes in pollution were estimated from value of a statistical life (VOSL) studies, which represented the willingness-to-pay of the population to reduce the risk of death of a random member of that population.
Direct costs The only direct costs included in the analysis were the hospital admissions for respiratory disease and the cost per catalyst. Hospital admission costs were represented by average UK National Health Service hospital admission costs for respiratory illness. Costs for catalysts were based on the recommended retail price for a replacement catalyst. The capital costs of catalysts were then annualised at a rate of 6%, as this was the UK public sector discount rate. The price year was 1998.
Statistical analysis of costs The costs were treated as point estimates (i.e. the data were deterministic).
Indirect Costs The indirect costs were not included in the analysis.
Currency UK pounds sterling (). The authors reported that a 1998 US$ equivalent could be derived using a purchasing power parity adjusted exchange rate of 0.66 (i.e. 1,998 divided by 0.66).
Sensitivity analysis One-way sensitivity analyses were undertaken by varying the base-case VOSL ($1.49 million) between 2.66 and 3.87 million.
Estimated benefits used in the economic analysis By 1998, the estimated benefit of VECs in the UK was 1,317 million (inclusive of costs of changes in hospital admissions).
By 2005, the estimated benefit of VECs in the UK was 5,101 million (inclusive of costs of changes in hospital admissions).
Cost results The present value of costs of VECs was 808.15 in 1998 and 2,944.5 by 2005.
Synthesis of costs and benefits The costs and benefits were combined by calculating the total net benefits of catalyst costs. The estimated net societal health benefits were 509.61 million by 1998 and 2,156.9 million by 2005.
The results of the sensitivity analysis showed that increasing the VOSL to 2.66 million increased the social net benefits to 1,533 million in 1998 and to 6,108 million by 2005. Increasing the VOSL to 3.87 million further increased the net social benefits to 2,588 million by 1998 and to 10,207 million by 2005.
Authors' conclusions The results suggested that there were substantial health benefits, in excess of the cost of vehicle emission catalysts (VEC), between the periods 1993 to 1998 and 1993 to 2005.
CRD COMMENTARY - Selection of comparators A justification was given for using the no-VEC intervention as the comparator. It represented the current situation in the UK before VECs became compulsory. However, the authors acknowledged that alternative policies or actions might conceivably have led to larger benefits or a reduction in costs. You should determine if the comparator used represents current practice in your own setting or whether other comparators could also have been relevant.
Validity of estimate of measure of effectiveness Although the authors did not explicitly report that a systematic review of the literature had been undertaken to identify relevant research and minimise biases, it appears that a thorough and comprehensive review has been undertaken. The authors included more than 40 primary studies in their review and also used the opinion of relevant experts. Any assumptions made in the analysis were appropriately reported in the main paper. However, given the number of extrapolations required to assess the health impact of VECs in the future, the authors should have undertaken exhaustive sensitivity analyses to assess the impact of their projections; such analyses were not undertaken.
Validity of estimate of measure of benefit The estimation of benefits was modelled. The authors appropriately reported the sources were monetary valuations for the health benefits (i.e. mortality and morbidity) derived. Further, the authors reported the health benefits both in their natural units and in monetary terms, which will enhance the generalisability of the results to other settings.
Validity of estimate of costs It was unclear whether all cost categories relevant to the societal perspective adopted were included in the analysis. For example, the authors did not include the productivity losses occurring because of pollution morbidity and mortality. However, they might not have included such costs because they were captured in the willingness-to-pay estimates to prevent a death or a hospital admission. The authors should have made this point clear in their study. The costs and the quantities were not reported separately, which will limit the generalisability of the authors' results. The costs were derived from published sources. Very limited sensitivity analyses were undertaken, and only the value of a statistical life used to value one prevented death was varied. All relevant costs that were incurred in the future (e.g. VECs) were appropriately discounted and the price year was reported. This will aid any future inflation exercises.
Other issues The authors compared their results with those from other UK studies that found reductions in pollutants to be associated with an increase in health benefits. The issue of generalisability to other settings was not addressed. The authors do not appear to have presented their results selectively and their conclusions reflected the scope of the analysis. The authors reported a number of further limitations to their study. First, the results are likely to err on the side of caution since the authors aimed to reduce the risks of overestimating net health benefits, with estimates being excluded where there was significant uncertainty about relationships and/or parameters or other data. Second, the authors constrained their analysis to the effects of local urban air pollution. Finally, the authors did not include the effects of VECs on other pollutants such as carbon monoxide.
Implications of the study The authors reported that VECs might increase the level of platinum in the atmosphere, which warrants continued monitors. They also suggest the conduct of "ante evaluations of sets of alternative environmental policy interventions, to assist in the development of effective, appropriate pollution control policy strategies, as well as ex post appraisals of the net benefits realized from the chosen instrument(s)".
Source of funding CASE Research Studentship from the UK Economic and Social Research Council with the British Geological Survey.
Bibliographic details Hutchinson E J, Pearson P J. An evaluation of the environmental and health effects of vehicle exhaust catalysts in the UK. Environmental Health Perspectives 2004; 112(2): 132-41 Other publications of related interest COMEAP. Department of Health Committee on the Medical Effects of Air Pollutants. Quantification of the effects of air pollution on health in the United Kingdom. London: The Stationery Office; 1998.
Department of Environment Transport and the Regions. Cost benefit analysis of lead in drinking water. Final report. DETR; 1997
Indexing Status Subject indexing assigned by NLM MeSH Catalysis; Cost-Benefit Analysis; Environment; Great Britain; Health Care Costs /statistics & Humans; Models, Theoretical; Palladium /analysis; Platinum /analysis; Public Health /economics; Rhodium /analysis; Urban Population; Vehicle Emissions /adverse effects /prevention & control; numerical data AccessionNumber 22004006321 Date bibliographic record published 28/02/2007 Date abstract record published 28/02/2007 |
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