Richard C. Schwing

HUMAN BEHAVIOR AND TRAFFIC SAFETY

Contains the paper and discussions from the symposium on human behavior and traffic safety, held at the general motors research laboratories on September 23-25, 1984.

Instabilities of Regression Estimates Relating Air Pollution to Mortality

The instability of ordinary least squares estimates of linear regression coefficients is demonstrated for mortality rates regressed around various socioeconomic, weather and pollution variables. A ridge regression technique presented by Hoer1 and Kennard (Technometrics 12 (1970) 69–82) is employed to arrive at “stable” regression coefficients which, in some instances, differ considerably from the ordinary least squares estimates. In addition, two methods of variable elimination are compared—one based on total squared error and the other on a ridge trace analysis.

Measures of association of some air pollutants, natural ionizing radiation and cigarette smoking with mortality rates.

Two methods are employed to estimate the association the association of hydrocarbons, sulfur compounds, nitrogen compounds, natural ionizing radiation, and cigarette smoking with some age stratified and disease specific United States mortality rates for white males. The first method is based on a ridge regression technique and the second on a sign constrained least squares analysis. The measure of association between these environmental factors and mortality are quantified as elasticities; i.e., the indicated percentage change in the average mortality rate corresponding to a 1% change in the average level of environmental factor. Elasticities are estimated for age specific and disease specific mortality rates, and these values are then aggregated and compared to estimates corresponding to total mortality rates. Overall, consistent results are obtained using the above methods for sulfur compounds and cigarette smoking. Many of these results differ considerably from corresponding results obtained from the ordinary least squares regression analysis, highlighting the need for applying the appropriate estimation methods. In addition to the variables already specified, these analyses take into consideration the following groups of explanatory variables: Climate--Precipitation, January temperature, July temperature, humidity, and solar radiation. Socioeconomic--Age, education, sound housing, population per household, population density, % non-white, % white-collar, income, and city size.

BENEFIT-COST ANALYSIS OF AUTOMOTIVE EMISSION REDUCTIONS

Abstract This study examines the optimum automotive emission control levels within a marginal benefit-cost framework. We assume that benefits consist of market and nonmarket components. Cost of control is estimated from historical and projected data as published in the literature. The results of the analyses indicate that even with a high estimate of benefits, the economically optimal vehicle emission levels are strikingly less severe than those required by the 1970 Clean Air Act.

Air pollution-mortality models: A demonstration of the effects of random measurement error

Errors of measurement have long been recognized as a chronic problem in statistical analysis. Although there is a vast statistical literature of multiple regression models estimating the air pollution-mortality relationship, this problem has been largely ignored. It is well known that pollution measures contain error, but the consequences of this error for regression estimates is not known. We use Lave and Seskins air pollution model to demonstrate the consequences of random measurement error. We assume a range of 0% to 50% of the variance of the pollution measures is due to error. We find large differences in the estimated effects on mortality of the pollution variables as well as the other explanatory variables once this measurement error is taken into account. These results cast doubt on the usual regression estimates of the mortality effects of air pollution. More generally our results demonstrate the consequences of random measurement error in the explanatory variable of a multiple regression analysis and the misleading conclusions that may result in policy research if this error is ignored.

Electrification due to high-velocity liquids and mists: Experimental results for CHClF2 and CCl2F2 and their mixtures

Abstract Charge generation rates have been measured for two halocarbons and their mixtures, having electrical conductivities ranging from 7.5 × 10−12 to 2 × 10−15 ohm−1 cm−1. These fluids were passed through a 1.55 mm diameter tube as a liquid and as a mist at high velocity at ambient temperatures. Owing to the high vapor pressures of the materials, a closed system capable of operating at pressures up to 30 atm was utilized. In tubes 140 cm long, mist flow was found to produce significantly higher currents than liquid flow at the same mass flow rate. In a sequence of eight short tubes, insulated from one another and totaling 140 cm, the absolute magnitudes of the current generated by mist flow in each tube were comparable to the current magnitudes generated by liquid flow. However, the sum of currents from all eight segments was lower for liquid flow than for mist flow owing to the canceling effect of polarity changes along the length of the tube. Current generation rates by liquid flows were found to be comparable to values calculated with the equations of Gavis and Koszman.

Fatality Incidence Stratified by Driver Behavior: An Exploratory Analysis with FARS Data

Driver behavior indicators were used to stratify FARS (Fatal Accident Reporting System) data on occupant fatalities. Data for automobiles, vans, and light trucks were stratified by: single or multiple vehicle accident driver use of alcohol driver use of safety belt

Electrical Current Generation by the Flow of Refrigerants

Charge generation rateshavebeenmeasured fortwo halocarbons andtheir mixtures, having electrical conductivities ranging from7.5X 10-12 to2 X 10-10-1-cm-i.Thesefluids were passed through a1.55-mm diameter tubeasaliquid andasamistat highvelocity atambient temperatures. Duetothehighvaporpres- suresofthematerials, aclosed systemcapable ofoperating atpres- sures upto30atmospheres wasutilized. Intubes140cmlong, mistflowwasfoundtoproduce significantly higher currents thanliquid flowatthesamemassflowrate. Ina sequence of8short tubes, insulated fromoneanother andtotaling 140 cm,theabsolute magnitudes ofthecurrent generated bymistflow ineachtubewerecomparable tothecurrent magnitudes generated byliquid flow. However, thesumofcurrents fromall 8segments was lower forliquid flowthanformistflowduetothecancelling effect of polarity changes along thelength ofthetube. Current generation ratesbyliquid flows werefound tobecompa- rable tovalues calculated using theequations ofGavisandKoszman.