Authors of the study, published this month in the Annals of Emergency Medicine, took pains to say they were not calling into question the abilities of emergency medical services personnel, who are members of the Fire Department. Trained EMS squads, they said, are especially valuable for heart attacks, strokes, accidents, and other non-shooting cases, which account for the vast majority of distress calls.
"I think they do a great job," said Penn physician Roger A. Band, the study's lead author and a former emergency medical technician in Florida and Virginia.
Yet in a city where ambulances are at times scarce, police sometimes get to the scene of a shooting first. The data suggest that "scoop and run" - the practice of police transporting patients - is a good alternative.
Police Deputy Commissioner Kevin Bethel, who oversees patrol operations, welcomed the findings.
"This just reaffirms that what we're doing is the right thing," Bethel said. "We know what the Fire Department does. We know they do a yeoman's job, but they can't do it all."
Fire Department officials did not respond to several requests for comment, though in the past they have publicly supported the assistance from police.
The study included 4,122 patients who had been shot or stabbed, of whom 2,961 were transported by ambulance and 1,161 by police car to eight trauma centers.
The authors did not answer the question of why gunshot victims taken by police fared a bit better.
Band, an assistant professor of emergency medicine at Penn's Perelman School of Medicine, said the reason could be that police get to the scene faster. But he stressed that he could not say for sure, as the study authors did not have data on how long it took police to deliver the injured to emergency rooms.
Joe Schulle, president of the International Association of Fire Fighters Local 22, which represents city firefighters and ambulance personnel, said time is of the essence.
"If you're within five minutes of a trauma center, then it may be more beneficial just to get you into the hospital" via police car, he said. "In a lot of cases when someone's bleeding to death, it's going to take a medic 10 minutes to get to the scene."
Amy J. Goldberg, chief of trauma at Temple University Hospital, countered that the key factor may not be time after all.
Goldberg, who was not involved in the Penn research but has studied the issue, said two traditional forms of ambulance treatment are no longer considered beneficial for gunshot victims: inserting a breathing tube and administering intravenous fluids.
She cited a study last year in which she and coauthors compared the results for gunshot and stabbing victims transported to the hospital by basic life-support ambulances with the results for those taken by advanced life support.
Patients in the latter type of ambulance were much more likely to get a breathing tube or other interventions, but were less likely to survive, the study found. Insertion of a breathing tube tends to lower the amount of blood going to the heart - a problem for those who already have lost a lot of blood.
Like the Penn authors, Goldberg stressed that the findings applied only to gunshot and stab wounds in an urban environment with many trauma centers.
The Penn study also looked at stab wounds. When the authors considered all cases of "penetrating trauma" - gunshots and stabbings - the survival rates for those taken by police and those going by ambulance were statistically equivalent.
However patients get to the emergency room, Schulle said, more ambulance squads are needed.
On Saturday afternoon, the Fire Department's communications center sent out a notice that all medic units were busy responding to calls, that no further squads were available. Lately, Schulle said, such alerts have been issued about once a week.