Bias-by-selection: The accuracy of an unbiased estimator

Hauer, Ezra; Byer, Philip H.; Joksch, H C

doi:10.1016/0001-4575(83)90011-8

Cited by 7 publications

(4 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…One possible adjustment procedure that has been developed by Hauer and others (Hauer, 1980a(Hauer, , 1980b(Hauer, , 1986Hauer, Bayer and Joksch 1983;and Persaud and Hauer 1984) is based on the following assumptions: (i) accidents at an intersection occur according to a Poisson process; and (ii)the mean of the Poisson process varies from intersection to intersection according to a Gamma distribution. These assumptions and Bayes' theorem lead to the following relationship:…”

Section: Empirical Bavesian Estimationmentioning

confidence: 99%

A Methodology for estimating traffic safety improvements at intersections

Ben‐Akiva¹,

Ceder

Cheng³

et al. 1999

J of Advced Transportation

View full text Add to dashboard Cite

Intersection accidents represent a significant proportion of overall motor vehicle accidents. More accurate estimates of the actual effectiveness of intersection safety improvements are required.This study develops an improved methodology for postimplementation evaluation of safety countenneasures at intersections. Accidents are random, rarely occurring events. For a given time period, this leads to random fluctuations in accident frequencies, which suggests that statistical analysis employing confidence intervals, rather than point estimates, is required. Two technical problems complicate this treatment of accident occurrence as a random variable. The first problem is that identifying of hazardous locations is generally based on above-average accident frequency during the most recent period(s) for which data is available. The second problem arises from changes in external factors such as traffic volume, motor vehicle safety standards, etc., during the period of analysis, which may also affect traffic safety.A "combined" approach which addresses these technical issues is developed. Empirical Bayesian methodology is combined with regression techniques to derive a more accurate measure of the effect of safety treatments. An important consideration is the derivation of the variance of this measure, so that appropriate confidence intervals may be constructed. The approach is then applied to a sample of locations that underwent treatment by the Massachusetts Department of Public Works (MDPW). We compare our results to those which might be obtained using alternative methodologies that correct for neither or only one of the technical problems. We also illustrate how preliminary conclusions may be drawn regarding the effectiveness of broad categories of treatments, and how individual sites requiring further investigation may be identified.

show abstract

Section: Empirical Bavesian Estimationmentioning

confidence: 99%

A Methodology for estimating traffic safety improvements at intersections

Ben‐Akiva¹,

Ceder

Cheng³

et al. 1999

J of Advced Transportation

View full text Add to dashboard Cite

show abstract

“…It is also interesting to determine the dispersion obtained in the truncated Poisson distribution, which, of course, is less than the dispersion in an unrestricted Poisson distribution. Making use of the results of Hauer et al [1983] it can be shown that the variance of X ' is…”

Section: Qk(m)mentioning

confidence: 99%

“…Hauer [1980aHauer [ , 1980b has described the problem with regression effects in many ways and has given a method for estimating the effects (see Section 4.1). Hauer et al [1983] have studied the accuracy of the proposed estimator. Hauer s method is founded on a mathematical model specifying the number of accidents to be truncated Poisson distributed in the before-period.…”

Section: Introductionmentioning

confidence: 99%

A comparison of two methods for estimating the effect of a countermeasure in the presence of regression effects

Danielsson

1986

Accident Analysis & Prevention

View full text Add to dashboard Cite

The report studies the problem of estimating in a non-experimental before-and-after investigation the effect of a countermeasure on the number of traffic accidents at road junctions. The accidents are assumed to occur according to a Poisson process with different intensities at different junctions. The junctions studied in this investigation are assumed to have been selected with the blackspot-technique, i.e. junctions with high numbers of accidents during the before-period have been chosen for the investigation. In the mathematical model this has the consequence that the number of accidents occurring during the before-period at a selected junction has a truncated Poisson distribution. During the after-period the number of accidents has a Poisson distribution (without restrictions), so that the number of accidents on the average decreases between the periods even if the countermeasure has no effect. The magnitude of this regression effect is studied in the report. The observed numbers of accidents during the before and after period are used to estimate the pure effect of the countermeasure both with an intuitive method and with the maximum likelihood method. The characteristics of the two methods of estimation are illustrated with the aid of simulation studies. In general the maximum likelihood method appears preferable, mainly because it produces estimates with higher precision.

show abstract

“…Además, estadísticamente, los accidentes son sucesos raros cuya distribución de probabilidad de frecuencias no se ajusta a la distribución Normal sino que se corresponde o con la distribución de Poisson o con la Binomial Negativa. Esto implica, en primer lugar, que para disponer de una muestra suficientemente significativa es necesario considerar períodos de tiempo más prolongados que en otros análisis estadísticos; habitualmente los períodos no deben ser inferiores a tres años (Permanent International Association of Road Congresses, World Road Association and PIARC Technical Committee on Road Safety, 2003) (tres años antes de la actuación y otros tres años después de la actuación) llegando a ser necesario un mínimo de 5 años en carreteras de menor tráfico (E. Hauer and P. Byer, 1983). Sin embargo, si los recursos son limitados un periodo de dos años puede ser aceptable (J.T.…”

Section: Aleatoriedadunclassified

Formulación de incentivos óptimos y viables para la mejora de la seguridad vial en concesiones de carreteras

Cruz¹

View full text Add to dashboard Cite

show abstract

Bias-by-selection: The accuracy of an unbiased estimator

Cited by 7 publications

References 2 publications

A Methodology for estimating traffic safety improvements at intersections

A Methodology for estimating traffic safety improvements at intersections

A comparison of two methods for estimating the effect of a countermeasure in the presence of regression effects

Formulación de incentivos óptimos y viables para la mejora de la seguridad vial en concesiones de carreteras

Contact Info

Product

Resources

About