Using data from the city’s OpenBaltimore catalog, University of North Florida student Robert Picard conducted a statistical experiment to determine whether city police are more prone to issuing speeding tickets toward the end of the month.
By the looks of it, there’s no confirmation bias here. The relevant graph is the final one Picard produced, which “actual” and “expected” tickets issued versus the day of the month. It’s a graph showing the three-year average calculated between 2009 and 2011. The positive bars on the graph indicate that more tickets were given than were expected. The negative bars indicate that fewer tickets were given than were expected.
So, are police issuing more tickets at the end of the month in order to fulfill some type of quota system? “Not exactly,” says Picard. His explanation is more an interpretation than anything else:
It may look like a quota system would explain the patterns we see in the data, but you could probably come up with another explanation that seems to fit the data too. It’s also worth noting that a quota system wouldn’t really explain the drop on the 31st . . .
The StatWing blog, which took a more nuanced look at Picard’s analysis, comes up with a similar conclusion — there’s no reason to think Baltimore city police are sticking it to the citizens at the end of each month — informed by a different interpretation:
The biggest problem with looking for evidence of quotas here is that we’re probably looking at the wrong data. Most of these offenses don’t appear to be ones that police have a whole lot of discretion around, as opposed to DUI pullovers or manually dispensed speeding tickets.