## The Annals of Applied Statistics

- Ann. Appl. Stat.
- Volume 5, Number 2B (2011), 1428-1455.

### Causal inference in transportation safety studies: Comparison of potential outcomes and causal diagrams

Vishesh Karwa, Aleksandra B. Slavković, and Eric T. Donnell

#### Abstract

The research questions that motivate transportation safety studies are causal in nature. Safety researchers typically use observational data to answer such questions, but often without appropriate causal inference methodology. The field of causal inference presents several modeling frameworks for probing empirical data to assess causal relations. This paper focuses on exploring the applicability of two such modeling frameworks—Causal Diagrams and Potential Outcomes—for a specific transportation safety problem. The causal effects of pavement marking retroreflectivity on safety of a road segment were estimated. More specifically, the results based on three different implementations of these frameworks on a real data set were compared: Inverse Propensity Score Weighting with regression adjustment and Propensity Score Matching with regression adjustment versus Causal Bayesian Network. The effect of increased pavement marking retroreflectivity was generally found to reduce the probability of target nighttime crashes. However, we found that the magnitude of the causal effects estimated are sensitive to the method used and to the assumptions being violated.

#### Article information

**Source**

Ann. Appl. Stat., Volume 5, Number 2B (2011), 1428-1455.

**Dates**

First available in Project Euclid: 13 July 2011

**Permanent link to this document**

https://projecteuclid.org/euclid.aoas/1310562728

**Digital Object Identifier**

doi:10.1214/10-AOAS440

**Mathematical Reviews number (MathSciNet)**

MR2849781

**Zentralblatt MATH identifier**

1223.62175

**Keywords**

Causal inference potential outcomes causal Bayesian networks observational studies transportation safety nighttime crash data

#### Citation

Karwa, Vishesh; Slavković, Aleksandra B.; Donnell, Eric T. Causal inference in transportation safety studies: Comparison of potential outcomes and causal diagrams. Ann. Appl. Stat. 5 (2011), no. 2B, 1428--1455. doi:10.1214/10-AOAS440. https://projecteuclid.org/euclid.aoas/1310562728

#### Supplemental materials

- Supplementary material: Supplement to “Causal inference in
transportation safety studies: Comparison of potential
outcomes and causal diagrams”. This document contains additional details about
the Matching and Inverse Propensity score estimators and
the top ten graphs recovered by the graph learning
algorithm.Digital Object Identifier: doi:10.1214/10-AOAS440SUPP