The most dangerous days of the year

on Dec 18, 2012
When looking at days of the year with the most homicides a pattern jumps out: violence is significantly higher during certain holidays in Mexico compared to the rest of the year. This is a well studied pattern in other countries.

Most violent dates 1998-2007:
Date Homicides
2000-Jan-01 93
1998-Dec-25 92
2001-Jan-01 89
1999-Jan-01 88
2005-Jan-01 80
1999-Dec-25 78
1998-Mar-01 76
1998-Jun-14 74
1998-Oct-25 73
1998-Nov-29 73

Six of the ten most violent days from 1998 to 2007 where either the first day of the year or Christmas. To check whether holidays were really more violent than the rest of the year I plotted the total number of homicides for the period 1998-2003, and 2005 (so each day after February would fall exactly once each day of the week). I excluded the drug war years to make the pattern more obvious.
Sum of daily homicides from 1998-2003, and 2005 (ten most violent dates):
Total
Homicides
(Sum of All Dates)
Day
Number
Holiday
558 Jan-01 New Year
388 Dec-25 Christmas
357 Sep-16 Independence Day
281 Nov-02 Day of the Dead
270 Feb-15 Day After Valentine's Day
270 Dec-12 Virgin of Guadalupe
269 Dec-24 Christmas Eve
263 May-10 Mother's Day
259 Dec-31 New Year's Eve
256 May-03 Related to Labor Day?

I find it quite interesting that the day of the dead would be one of the most violent days of the year. In countries where most homicides are solved, most homicide victims knew their attacker, so perhaps hanging out with family and friends during the holidays is not such a good idea? Does that stress people out?

Performing an analysis of variance and testing for multiple comparisons with a Tukey test, the list of holidays above (coded as a binary variable), controlling for month of year and day of week, were expected to have between 28 and 39 extra homicides with a point estimate of 33 homicides.

fit <- aov(total.deaths ~ as.factor(holiday) + as.factor(month(date)) + as.factor(wday), 
            data = homicides)
TukeyHSD(fit)

Results for all days from 1998 to 2007:
##   Tukey multiple comparisons of means
##     95% family-wise confidence level
## 
## Fit: aov(formula = total.deaths ~ as.factor(holiday) + as.factor(month(date)) + as.factor(wday), data = homicides)
## 
## $`as.factor(holiday)`
##             diff   lwr   upr p adj
## TRUE-FALSE 33.46 28.37 38.55     0
##
## $`as.factor(wday)`
##         diff      lwr       upr  p adj
## 2-1 -11.9148 -13.3360 -10.49355 0.0000
## 3-1 -16.9419 -18.3645 -15.51927 0.0000
## 4-1 -18.3969 -19.8188 -16.97494 0.0000
## 5-1 -17.6014 -19.0226 -16.18016 0.0000
## 6-1 -16.3855 -17.8068 -14.96427 0.0000
## 7-1 -11.1132 -12.5344  -9.69192 0.0000
## 3-2  -5.0271  -6.4490  -3.60516 0.0000
## 4-2  -6.4821  -7.9033  -5.06083 0.0000
## 5-2  -5.6866  -7.1072  -4.26605 0.0000
## 6-2  -4.4707  -5.8913  -3.05016 0.0000
## 7-2   0.8016  -0.6189   2.22219 0.6398
## 4-3  -1.4550  -2.8776  -0.03238 0.0411
## 5-3  -0.6595  -2.0815   0.76240 0.8188
## 6-3   0.5564  -0.8656   1.97829 0.9109
## 7-3   5.8287   4.4068   7.25064 0.0000
## 5-4   0.7955  -0.6258   2.21670 0.6489
## 6-4   2.0113   0.5901   3.43259 0.0006
## 7-4   7.2837   5.8625   8.70495 0.0000
## 6-5   1.2159  -0.2047   2.63645 0.1506
## 7-5   6.4882   5.0677   7.90880 0.0000
## 7-6   5.2724   3.8518   6.69292 0.0000
Sunday is 1

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Thank you for your interesting and insightful comments. I truly look forward to reading them.