Week before last, in my not-a-column, I wrote about the current debate over D.C. police staffing. My takeaway: The relationship between the number of officers in a given jurisdiction and its crime rate is tenuous at best, making rather specious any pronouncements of a certain “bloodbath” should policing levels decline marginally. Kristopher Baumann, the very able leader of the D.C. police officers union, responded in a Post op-ed, saying that more relevant data proves that fewer cops means more crime.

One thing that has been largely missing from this debate has been District-specific statistics. I cited a 2001 metastudy that looked at nearly two dozen studies of police staffing and crime from across the country. Baumann cited individual cities that have cut police officer in recent years, only to see a rise in crime. But how exactly have police staffing levels and crime levels interacted here in the District in the past decade or so?

Here is a graph showing the number of sworn officers versus the number of violent crimes and total crimes reported via the FBI’s Uniform Crime Report regime and published in MPD’s annual reports. From 1998 until 2010, the level of crime has declined dramatically (34 percent total; 25 percent for violent crime) while the number of police officers has modestly risen (11.7 percent):

(Data: Metropolitan Police Department annual reports)

But, some folks might rightly note that non-uniformed police personnel also affect a police force’s efficacy. Rightly so! So let’s do the same graph, this time with total MPD personnel instead of just sworn officers. The rise in total personnel has been more modest, about 8 percent:

(Data: Metropolitan Police Department annual reports)

Now, you might note: The city’s grown larger in the past 10 years; surely that should be taken into account. Surely it should! Here are staffing levels adjusted by the U.S. Census Bureau population estimates. The first thing you’ll notice is that how little that staffing levels changed over the past decade. For sworn officers, the year-to-year variance has been within a range of plus or minus 4 percent, hovering around an average of 658 officers per 100,000 residents. For total personnel, the variance has been plus or minus 5.8 percent:

(Data: Metropolitan Police Department annual reports)

(Data: Metropolitan Police Department annual reports)

When per-capita sworn officer levels were at their recent high, in 2004, response times were indeed low, at 2 minutes. But in 2008, with staffing essentially the same, response times rose to 8.4 minutes.

[UPDATE, 5/19, 6:35 P.M.: This post originally included a graph of emergency response times. Police Chief Cathy Lanier called to inform me that I had my data wrong, and indeed I had. I conflated the emergency response times measured in minutes from 2007 and later with the call pickup times measured in seconds from prior years. Lanier said she is writing a response that will have accurate response data.]

Meanwhile, while Lanier said that new development tends to bring new calls for police service, MPD stats show that total calls for emergency service have declined each year for the past five years, by a total of 9 percent.

What’s the takeaway from all the data? The relationship between police staffing and crime rates is not a direct correlation. There are instances year-to-year where crime went down when staffing went up. The opposite has also happened. But clearly there are other factors at work, whether economic, social, demographic or otherwise. The city has become more populated and more wealthy over the past decade, which also correlates to the declining crime rates.

Does that mean that Metropolitan Police staffing can be safely cut? If the force is allowed to dip to about 3,700 officers, as Mayor Vincent Gray’s budget proposal would, that would be the lowest ratio of police to residents in some 15 years. While the data shows that it’s hard to draw a direct correlation between crime rates and police staffing, look at it politically: If you’re an elected official and forces do conspire to raise crime rates, you probably don’t want to be the guy who cut cops to a historic low.