I only participate in one web forum, sponsored by the International Association of Crime Analysts. Once or twice a week, I will look over the posts, and from time to time I'll send a message off-list directly to someone who has posted a question. Occasionally, if I think something might have general interest to the group, I'll post my reply to the list.
Such was the case earlier this week, when an east coast analyst sought advice on how she might best contribute to a quarterly meeting at which police command staff members would be discussing proactive strategies to impact crime. This is a topic near and dear to me, that consumes a lot of space on the Director's Desk. Clicking the "Crime Analysis," "POP," or "Crime Prevention" tags in my label cloud would bring you to scores of posts on this topic.
My advice to her was to make friends with the Problem Oriented Policing Center's website, popcenter.org, and to help her commanders devise simple, straightforward evaluations to proactive strategies they implement. Evaluation is an important, yet often overlooked step in problem solving. I'm a huge believer in evidence-based practice, which demands assessing results so you can determine what works.
I have found a basic multiple time series to be one of the most practical ways to answer this question. In her post to the IACA forum, the analyst used the example of a preventative strategy to reduce larcenies from automobiles at certain apartment complexes. I'd think of evaluating that by collecting data on the volume of these crimes around the target locations before and after the intervention, then comparing that with the same time frames at other similar apartment complexes, and in the city as a whole.
In a couple of weeks, I'll be teaching my regular two-day course on this topic to recruits in the police academy, where two of the key questions they will grapple with in such scenarios are these: How will you know if it worked, and where will you get the data?