Driving Under the (Cellular) Inuence: Online Appendix

Call Likelihood. Beyond the primary data on callers from moving vehicles, two additional datasets of calls con…rm the price sensitivity of a broader population of cellular callers that extends beyond drivers. First, complete logs of cell phone activity for approximately 65 students and faculty over the academic years from 2004 and 2005 was obtained from the Reality Mining Project at the MIT Media Lab (MIT). 1 As part of a study examining the evolution of social networks and the transmission of information, researchers embedded surveillance technology in the cellular phones of each subject in their sample. Approximately 80,000 outgoing calls were logged over the course of the surveillance period. 2 Electronic logs ensure that the timing of calls are accurately documented to the second. The data may not be representative of the larger population across a variety of dimensions given that the subjects are primarily students. Figure A2 depicts the distribution of calls, aggregated in 10 minute bins, from 8 to 10pm for Mondays to Thursdays, Fridays and weekends. In order to formally estimate the size of the rise in call volume at the price threshold, the upper panel of Table A3 reports results of a Poisson regression of minute level calls from 8 to 10pm with …xed e¤ects that control for day of week, month and year of the call. The results indicate a rise in call likelihood of 22.6% in the hour after 9pm on Mondays and Thursdays and no signi…cant rise in the comparable period on Fridays or weekends. 3 The placebo checks for other hours indicate a rise at 8pm of about 12% and no rise at 10pm. However, the estimated rise at 8pm is not due to a discontinuous break at 8pm, but rather a gradual rise in calls from 8 to 9pm that may be idiosyncratic to this academic population. A second additional dataset (TNS) comprises over 741,000 calls made by 9,864 cell phone users from households across the country in 2000 and 2001. 4 The data was harvested from cellular phone bills voluntarily submitted from households randomly selected to participate in an earlier survey of telecommunications behavior and attitudes. 5 The data are hourly data and are from a 1 The data is described in 2 This period re ‡ects the fact that most subjects joined and remained in the sample during the academic year. A small fraction of calls were made in …