Age-Period-Cohort models and the decline of violence

on Oct 9, 2012
Ever since the end of the Mexican Revolution and the Cristero War violence in Mexico inched down in fits and starts from a high of about 60 homicides per 100,000 people to its lowest level sometime during the middle of the last decade (there's some uncertainty about the number of homicides in 2007). Then, the drug war happened and the homicide rate shot straight up.

After reading The Better Angels of Our Nature: Why Violence Has Declined, by Steven Pinker, and looking at reviews of the literature on homicide decline in Europe, it seemed to me as if some of the posited reasons for the decline of violence would involve strong cohort effectseach generation successively becoming less and less violent. This immediately reminded me of Mexico, and so I decided to take a quick look at the data:
Each cohort group is connected by a loess line(only ages 12-60 are shown in the graph)