Descriptive Statistics

The upper half of Table 2.1 provides the overall distribution of crimes that occurred across Philadelphia for the 14 years from 1998 to 2011. Overall, more than a million incidents occurred across the city during that period. One-quarter were violent crimes, while about two-thirds were property offenses. The "All Thefts" property-crime category comprised half the total crime incidents. Incidents occurring on Sundays made up nearly one-seventh of the total.

The overall crime distribution pattern largely holds for a subset of interest ― crime incidents occurring within the 1/8 mile radius areas of the entire sample (the lower half of Table 2.1). This subset covered only 3.2% of the total crime incidents. Property- crime incidents were still dominant, and the overall share of Sunday crime incidents was around 12%. The proportion of Sunday property crime incidents over the total crime incidents for these subset areas was higher than that for the entire city ― 74.7%,

compared to 68.5%. Instead, Sunday violent-crime incidents for the subset areas occupied a smaller share of the Sunday total, 22.1% compared to 28.8%.

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Table 2-1. Types and Numbers of Crime Incidents, According to Days of the Week

On all days of the

week On Sundays

Sunday shares of crime incidents

Crime incidents occurring across the entire City of Philadelphia

Total Crime 1,071,256 [100%] 139,647 [100%] 13.0% Violent Crime 267,299 [25.0%] 40,278 [28.8%] 15.1% Homicide 5,644 956 16.9% Aggravated Assault 129,612 21,051 16.2% Robbery 132,043 18,271 13.8% Property Crime 733,573 [68.5%] 88,927 [63.7%] 12.1% Burglary 159,351 18,961 11.9% All Thefts 574,222 69,966 12.2% Misdemeanor 70,384 [6.6%] 10,442 [7.5%] 14.3% Disorderly Conduct 65,343 9,735 14.9% Public Drunkenness 5,041 707 14.0%

Crime incidents occurring within the 1/8 mile radius areas of the 31 W&S stores

Total Crime 34,038 [100%] 4,221 [100%] 12.4% Violent Crime 6,572 [19.3%] 932 [22.1%] 14.2% Homicide 114 18 16.0% Aggravated Assault 2,700 448 16.6% Robbery 3,758 466 12.4% Property Crime 25,429 [74.7%] 2,978 [70.6%] 11.7% Burglary 3,753 479 12.8% All Thefts 21,676 2,499 11.5% Misdemeanor 2,037 [6.0%] 311 [7.4%] 15.3% Disorderly Conduct 1,731 282 16.3% Public Drunkenness 306 29 9.5%

Note: Only 3.2% of the total crime incidents occurring across the Philadelphia city (=33,830/1,071,256) occurred within the 1/8 mile radius areas of the 31 interested W&S stores. Percentages in brackets indicate shares of given crime categories' incident numbers over the total crime incident numbers.

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Given the 158,503 observation sample size for the DDD model (=5,113 days*31 stores), the volumes of individual crime incidents occurring within the 1/8 mile radius areas of the W&S stores were too low. Except for "All Theft," they had only several thousand non-Sunday incidents and hundreds of Sunday incidents. These low volumes might lead to imprecise estimations. To overcome this low volume limitation, the current study's outcomes were aggregated based on offense type: violent, property, misdemeanor, and total crimes. Note again that, despite the aggregation, the volumes of misdemeanor (N=1,988) and violent crime incidents (N=6,548) were still low, thus potentially leading to unstable and relatively imprecise estimations.

Table 2.2 provides the comparisons of average daily numbers of crime incidents. Notice that the values in cells indicated raw average numbers of crime incidents

occurring within a 1/8 mile radius of a W&S store for each day, without any control for confounding factors. Averages were calculated by dividing the summed numbers of relevant crime incidents for a given day of the week (Sunday or non-Sunday) during given periods (pre- or post-repeal) for given groups (treatment or control) by the relevant total numbers of days during given periods. The denominators were 1,865 days for the pre-repeal period (from January 1, 1998, to February 8, 2003) and 3,248 days for the post-repeal period (from February 9, 2003, to December 31, 2011).

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Table 2-2. Average Daily Crime Incidents Occurring within the 1/8 mile radius areas of the 31 W&S stores

Treatment Group:

6 W&S Stores allowed to open on Sundays since Feb. 9, 2003

Control Group:

25 W&S Stores not allowed to open on Sundays since Feb. 9, 2003

Pre-repeal (1/1/98~ 2/8/03) Post-repeal (2/9/03~ 12/31/11) Pre vs. Post Difference Pre-repeal (1/1/98~ 2/8/03) Post-repeal (2/9/03~ 12/31/11) Pre vs. Post Difference Total Crimes On Sundays 0.216 0.212 -0.004 0.208 0.164 -0.044 On non-Sundays 0.280 0.216 -0.064 0.247 0.196 -0.051 Violent Crimes On Sundays 0.037 0.031 -0.006 0.043 0.043 . On non-Sundays 0.038 0.032 -0.006 0.045 0.042 -0.003 Property Crimes On Sundays 0.178 0.154 -0.024 0.148 0.110 -0.038 On non-Sundays 0.227 0.170 -0.057 0.188 0.142 -0.046 Misdemeanors On Sundays 0.008 0.021 +0.013 0.017 0.011 -0.006 On non-Sundays 0.015 0.014 -0.001 0.014 0.011 -0.003

Note: The average daily numbers of crime incidents are calculated based on 5,113 days, of which the pre-repeal period was 1,865 days from 1/1/1998 to 2/8/2003 and the post-repeal period was 3,248 days from 2/9/2003 to 12/31/2011. A value in a cell represents a real average number of incidents.

Across the crime categories, differences between the pre- and post-repeal periods were noticeable. First, overall, the post-repeal period tended to have a lower volume of average daily incidents than the pre-repeal period, meaning that the general crime trend in Philadelphia was decreasing. Second, the absolute magnitudes of differences for crime incidents on non-Sundays were in general larger than those on Sundays except for misdemeanors. Third, the treatment group in general experienced large reductions in the non-Sunday crime incidents but relatively small reductions in the Sunday crime incidents after the repeal. Misdemeanor incidents even increased for the treatment group. On the other hand, the control group experienced rather similar reductions in both Sunday and

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non-Sunday crime incidents. Fourth, both the raw numbers and the absolute difference magnitudes for violent crime and misdemeanor incidents seem to be too small for a statistical test. Any statistical result for violent crime and misdemeanor incidents should be cautiously interpreted because the variations might be sensitive to small changes in incident numbers.

Figure 2.2 describes the trend of average yearly numbers of total crime incidents occurring within the 1/8 mile radius areas of both the treatment and control group W&S stores. For the average yearly numbers of Sunday total crime incidents (the upper part of Figure 2.2), the differences between treatment and control groups are relatively small before the repeal, but they became large after the repeal. One the other hand, the average yearly numbers of non-Sunday total crimes (the lower part of Figure 2.2), the differences between treatment and control groups remained relatively stable even after the repeal. These two trend graphs roughly suggest the possibility that the Sunday liquor sales ban repeal in 2003 may be associated with a crime increase.

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Figure 2-2. Average Yearly Total Crime Incidents Occurring within the 1/8 mile radius areas of the 31 W&S Stores

Note: The line between the years of 2002 and 2003 roughly indicates the quasi-experiment timing (repealing the Sunday liquor sales ban on February 9, 2003). The upper half depicts a trend of average yearly numbers of total crime incidents occurring on Sundays, and the lower half depicts those occurring on the other days of the week.

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2.4.2. Difference-in-Difference and Difference-in-Difference-in-Difference