Always_Ask_Questions,
“It’s the Phone, Stupid: Mobiles and Murder Lena Edlund and Cecilia Machado
NBER Working Paper No. 25883 May 2019
New York City, Los Angeles, and Chicago”
Yes, I already mentioned finding this paper above. But it says nothing about smartphone distractions being the potential cause of the link between cell phones and decreasing murder rates. The rates decreased starting in the late 1990s, which was a decade before Steve Jobs walked on stage. The study authors posit that the decreased murder rate was due to cell phones changing the illegal drug economy from street corner dealing to pre-arranged meet-ups, thus reducing the incidence of turf wars. And the Brazil paper seems to refer to a change in the number of phone number digits, not the introduction of cell phones.