Banning Cell Phones While Driving And A Lesson In Ceteris Paribus

The article is Report: Study shows cell phone bans don’t lower accident rates. A study found that states that banned using hand-held cell phones while driving did not see their accident rates go down compared to other states. But "Officials believe that drivers in areas with the ban have obtained hands-free devices, whose accident rates are at the same level as the hand-held devices." This means that all other factors were not held constant. We need ceteris paribus to be able to see if A causes B. We need to change just one thing, hand held cell phone use, without anything else changing. It is possible that this ban really does lead to fewer accidents but that the increased use of hands-free devices raised it back up.