The weekend shootings in Dayton, Ohio, and El Paso, where nine and at least 22 people were gunned down, respectively, clearly fits the term. But some readers wanted to know why two shootings on the West Side of Chicago over the weekend — one that injured seven people in Douglas Park and the other, just blocks away, that left one man dead and seven others injured — were not labeled as mass shootings. Here’s what some experts who study gun violence had to say about the issue: