Controlling for self-reported exposure in traffic accident prediction studies

Anders af Wåhlberg

Department of Psychology

Uppsala university

Exposure to risk of traffic accident

• As drivers drive, they expose themselves, and accident risk increases

Exposure to risk of traffic accident

• As drivers drive, they expose themselves, and accident risk increases

• When differences in accident record is predicted, what is it we predict?

Exposure to risk of traffic accident

• As drivers drive, they expose themselves, and accident risk increases

• When differences in accident record is predicted, what is it we predict?

• Accident proneness, exposure proneness, or both?

Exposure to risk of traffic accident

• As drivers drive, they expose themselves, and accident risk increases

• When differences in accident record is predicted, what is it we predict?

• Accident proneness, exposure proneness, or both?

• Most studies on accident record do not control for exposure beyond calender time

Exposure to risk of traffic accident

• Is exposure a mediator or a confounder?

Exposure to risk of traffic accident

• Is exposure a mediator or a confounder?

• If exposure does not correlate with the predictor, it is a confounder

Exposure to risk of traffic accident

• Is exposure a mediator or a confounder?

• If exposure does not correlate with the predictor, it is a confounder

• What psychological variables correlate with exposure?

Exposure to risk of traffic accident

• Is exposure a mediator or a confounder?

• If exposure does not correlate with the predictor, it is a confounder

• What psychological variables correlate with exposure?

• What is the difference if we control for exposure?

Self-reported exposure to risk of traffic accident

Self-reported exposure to risk of traffic accident

• Is self-reported mileage a mediator or a confounder?

Self-reported exposure to risk of traffic accident

• Is self-reported mileage a mediator or a confounder?

• Self-reported mileage is unreliable

Self-reported exposure to risk of traffic accident

• Is self-reported mileage a mediator or a confounder?

• Self-reported mileage is unreliable

• Self-report bias can create associations with other variables

Study: Controlling for self-reported mileageMethod

Study: Controlling for self-reported mileageMethod

• Samples: 4 (total N=24 016)

Study: Controlling for self-reported mileageMethod

• Samples: 4 (total N=24 016)

• Self-reported crashes and offences

Study: Controlling for self-reported mileageMethod

• Samples: 4 (total N=24 016)

• Self-reported crashes and offences

• Questionnaires scales: DAS, DBI, SSS, drugs, DBQ-V, DIM

Study: Controlling for self-reported mileageMethod

• Samples: 4 (total N=24 016)

• Self-reported crashes and offences

• Questionnaires scales: DAS, DBI, SSS, drugs, DBQ-V, DIM

• Analysis: Comparing zero-order and partial correlations between crashes/offences and scales, controlling for mileage

Study: Controlling for self-reported mileageResults

Study: Controlling for self-reported mileageResults

• 20% reduction in explained variance for crashes

Study: Controlling for self-reported mileageResults

• 20% reduction in explained variance for crashes

• 30% reduction in explained variance for offences

Conclusions

Conclusions

• There is a strong effect of exposure on crash prediction in self-reported data

Conclusions

• There is a strong effect of exposure on crash prediction in self-reported data

• Most studies on accident prediction use self-reported data

Conclusions

• There is a strong effect of exposure on crash prediction in self-reported data

• Most studies on accident prediction use self-reported data

• Few accident prediction studies control for exposure beyond calender time

Conclusions

• There is a strong effect of exposure on crash prediction in self-reported data

• Most studies on accident prediction use self-reported data

• Few accident prediction studies control for exposure beyond calender time

• Therefore; effect sizes have been over-estimated for many variables

Thank you for your attention

Anders af Wåhlberg

Department of Psychology

Uppsala university