Cooking the Books - A Second Look

February 19, 2010
Posted by Jay Livingston

Do the police undercount crime?

The graph I cribbed from Rick Rosenfeld in yesterday’s post showed a remarkable similarity between victimization surveys and official crime statistics. In 2000, for example the rate of reported burglaries according to the NCVS was nearly identical to the UCR rate. Both were about 4.4 per 1,000.

Yet in the recent Eterno-Silverman study, police commanders, responding anonymously, said that crime statistics were suppressed. And Josh in his comment yesterday refers to Peter Moskos’s “let me count the ways” description of how the police keep crimes off the books. (See Moskos’s own take on the study at his website.)

The problem is that the graph I presented was somewhat misleading The NCVS and UCR rates of burglary do not measure exactly the same thing. It’s not exactly oranges and apples; more like oranges and tangerines.

1. The NCVS data are for the New York metro area, so we have to use similar UCR data even though the rap about fudging the stats is only about the NYPD. No way to get around that problem

2. More crucially, the NCVS counts only residential burglaries; the UCR number includes both commercial and residential burglaries. Nationwide, about 2/3 of all UCR burglaries are residential. Using that figure for the New York area we get a UCR rate for Residential burglaries of only 3.0 per 1,000 population, about one-third less than we would expect from the estimate of the number of residential burglaries that victims say they reported. Here’s an amended graph. I’ve added a line for residential burglaries that uses the simple 2/3 formula.

(Click on the graph for a larger view.)

The rate of residential burglaries that victims say that they report is usually one-and-a-half to two times greater than the rate of residential burglaries officially “known to the police.” For the year 2000, the NCVS rate of 4.4 per 1,000 population works out to 40,000 reported residential burglaries. If 2/3 of burglaries are residential, only 27,500 of those made it onto the police books.

Does that mean that the police canned 12,5000 reported burglaries? Probably not. There may be other explanations for the some of the discrepancy. But the data do provide some support for those who are skeptical of the precision of the police numbers.


PCM said...

"If 2/3 of burglaries are residential"

That's an awfully big "if." I can think of million reasons (or at least 3) that NYC may not be similar to the national average on that one.

I think extrapolating from a stat like that is fraught with risk, to say the least.

Jay Livingston said...

Peter, Of those 40,000 burglaries known to the police in the NY MSA, I arbitrarily guessed that 27,500 were residential. Do you think the actual number was higher or lower? More to the point, how can we get the actual data? The police departments must keep them, else how would the FBI know the national figure? You're the police guy; tell me where I can find those numbers.

PCM said...

Email me if you want and we can try and figure it out.