The aim of research into cell phone tasks is to obtain an unbiased estimate of their relative risk (RR) for crashes. This paper re-examines five RR estimates of cellular conversation in automobiles. The Toronto and Australian studies estimated an RR near 4, but used subjective recall to estimate driving times. The OnStar, 100-Car, and a recent naturalistic study used objective measures of driving times and estimated an RR near 1, not 4 — a major discrepancy. Analysis of data from GPS trip studies shows that subjects were in-car only 20% of the time on a previous day, given they were in-car at the same clock time on a subsequent day. Hence, the Toronto estimate of driving time during control windows must be reduced from 10 to 2 min. Given a cell phone call rate about 7 times higher when in-car than out-of-car, and correcting for misclassification of some post-crash calls as pre-crash, the Toronto adjusted RR is 0.61, and the Australian 0.64, agreeing with the OnStar estimate of 0.62. After adjustment for bias, all five RR estimates for cellular conversation while driving in automobiles are near 1, with a pooled RR of 0.61 (95% confidence interval 0.51 to 0.74). (Author/publisher)
Samenvatting