United States Department of Transportation
i
The Use of Mixed Effects ANCOVA to Characterize Vehicle Emission Profiles
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2000-09-01
[PDF-136.49 KB]
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Abstract:A mixed effects analysis of covariance model to characterize mileage dependent emissions profiles for any given group of vehicles having a common model design is used in this paper. These types of evaluations are used by the U.S. Environmental Protection Agency to certify whether or not new models conform to existing emissions standards. The statistical models introduced describe both the average emissions profile for a group of vehicles as well as an accounting for individual vehicle variability within the group. Realistic confidence bounds for an average emissions deterioration profile within a given group can also be provided to allow accurate emissions comparison of multiple groups. Sample of emissions data is presented for two types of vehicles: natural gas Dodge Ram vans and gasoline Dodge Ram vans (all from the 1992-94 model years). Additionally, the population profile for nonmethane hydrocarbons is explored.
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