Cumulative Abnormal Returns Delta, United, and American Airlines announced purchases of planes on July 18 (7/18), February 12 (2/12), and October 7 (10/7), respectively. Given the following information, calculate the cumulative abnormal return (CAR) for these stocks as a group. Graph the result and provide an explanation.

All of the stocks have a beta of 1, and no other announcements are made.

Delta United American Date Market Return Company Return Date Market Return Company Return Date Market Return Company Return 7/12 −.3 −.5 2/8 −.9 −1.1 10/1 .5 .3 7/13 .0 .2 2/9 −1.0 −1.1 10/2 .4 .6 7/16 .5 .7 2/10 .4 .2 10/3 1.1 1.1 7/17 −.5 −.3 2/11 .6 .8 10/6 .1 −.3 7/18 −2.2 1.1 2/12 −.3 −.1 10/7 −2.2 −.3 7/19 −.9 −.7 2/15 1.1 1.2 10/8 .5 .5 7/20 −1.0 −1.1 2/16 .5 .5 10/9 −.3 −.2 7/23 .7 .5 2/17 −.3 −.2 10/10 .3 .1 7/24 .2 .1 2/18 .3 .2 10/13 .0 −.1