Driving under the (Cellular) Influence
利用晚间9点话费折扣这一自然实验，发现司机通话概率在9点跃升7.2%，但事故率无相应变化，从而否定了此前研究中手机导致事故风险提高4.3倍的结论。
We investigate the causal link between driver cell phone use and crash rates by exploiting a natural experiment induced by the 9 pm price discontinuity that characterizes a majority of recent cellular plans. We first document a 7.2 percent jump in driver call likelihood at the 9 pm threshold. Using a prior period as a comparison, we next document no corresponding change in the relative crash rate. Our estimates imply an upper bound in the crash risk odds ratio of 3.0, which rejects the 4.3 asserted by Redelmeier and Tibshirani (1997). Additional panel analyses of cell phone ownership and cellular bans confirm our result.