In order to accurately compare 1970 to current-day they are taking away another changed variable: change in healthcare quality aka change in survival rates from violent crime/serious injuries.
Essentially, they are saying than many more people receive possibly fatal injuries annually current-day than did in annually in 1970. It is only the fact that health care is much better now (compared to 1970) that is the reason those people do not die, and therefore are not counted in the murder statistics. That counters the validity of the city official using specifically murder rates to prove that there is less violent crime. Rather, E would suggest that there is more violent crime, just less murders.
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In order to accurately compare 1970 to current-day they are taking away another changed variable: change in healthcare quality aka change in survival rates from violent crime/serious injuries.
Essentially, they are saying than many more people receive possibly fatal injuries annually current-day than did in annually in 1970. It is only the fact that health care is much better now (compared to 1970) that is the reason those people do not die, and therefore are not counted in the murder statistics. That counters the validity of the city official using specifically murder rates to prove that there is less violent crime. Rather, E would suggest that there is more violent crime, just less murders.