Over the study period, our research team was notified about 3,485 shootings occurring in Philadelphia. This translated into an average of 4.77 ± 2.82 shootings per day with a maximum of 21 shootings in a single day and an average of 9 days a year that were shooting-free. From among all these shootings, 3,202 (91.88%) were assaults, 167 were self-inflicted (4.79%), 60 were unintentional (1.72%), 54 were legal interventions (1.55%), and 2 were of undetermined intent (0.06%).
When considering only assaults, an average of 4.39 ± 2.70 individuals were shot per day in Philadelphia with a maximum of 20 in a single day and an average of 13 days a year in which no individuals were shot. These cases were geographically concentrated in a few areas of Philadelphia (). For use in our study, we excluded assault cases who were under 21 years of age or of unknown age (29.83%), non-Philadelphia residents (4.34%), individuals not described as being Black or White (1.62%), and police officers who had been shot (0.09%). From the remaining group of 2,073 participants, 677 (32.66%) were randomly selected and enrolled. Among all 677 enrolled shooting assaults, the case fatality rate was 18.46%. An age, race, and gender-matched group of 684 control participants were also concurrently identified and enrolled.
Kernel Density Maps of Assault and Self-Inflicted Shooting Cases and Controls in Philadelphia (White Space Indicates the Lowest Density and not Zero Density)
When considering only self-inflicted gun injuries, an average of 0.23 ± 0.47 individuals shot themselves each day in Philadelphia with a maximum of three in a single day and an average of 75 days each year in which individuals shot themselves. Geographically, these cases were relatively diffuse across Philadelphia (). For use in our study, we excluded self-inflicted cases who were under 21 years of age or of unknown age (7.19%), non-Philadelphia residents (1.80%), and individuals not described as being Black or White (2.39%). All 149 participants who remained were enrolled. The case fatality rate for these remaining participants was 91.89%. An age, race, and gender-matched group of 302 control participants were also concurrently identified and enrolled.
Geographically, both assault and self-inflicted control participants were found to be relatively diffuse across Philadelphia similar to the general population (). The median number of days between the time a shooting occurred and the time a control participant was recruited and interviewed to completion was 2 days, with more than 75% of all control participant interviews being completed within 4 days of the shooting. As a check of their recall, controls were also asked how certain they were of their location at the specific time of their index case’s shooting. In total, 94.10% reported that they were very sure of their location, 3.82% said they were sure, and 1.82% said they were not very sure or did not respond. The ability to recall their activities at the index time was also very similar for controls, with 95.77% reporting that they were very sure of key activities, 2.03% saying they were sure, and 1.15% saying they were not very sure or not responding.
Using standard formulae, the cooperation rate for our control survey was calculated to be 74.4% and the response rate 56.0% (Daves, 2006
). These rates exceeded those of other surveys conducted at about the same time (Galea & Tracy, 2007
) and were high enough to produce a reasonably representative sample of our target population (Groves, 2006
; Keeter, Kennedy, Dimock, Best, & Craighill, 2006
). Our respondents were also statistically similar to the general population of Philadelphia in terms of marital status, retirement, education, general health status, and smoking status within the age, gender, and race categories that they were matched (Southeastern Pennsylvania Household Health Survey, 2006
). Our controls were however found to be unemployed significantly more often than the general population.
Data collection and linkage efforts were largely successful for key variables related to shooting cases and controls. Among cases, all police and medical examiner records were successfully linked although only 35.03% of these linked records that went to a hospital were then able to be linked to hospital data. Gender, race, and age data were obtained for all cases. Data on the location of participants at the reference time were missing for 0.7% of cases and 4.2% of controls. Data on the location of participants’ homes were missing for 5.5% of cases and 3.0% of controls. A nontrivial proportion of data, however, were missing for shooters. For example, shooter gender was missing for 29.7% of cases, shooter race was missing for 30.9% of cases, shooter age was missing for 49.2% of cases, and shooters’ home addresses were missing for 37.5% of cases.