Metaphorically Speaking: Differential Diagnosis

"Common things happen commonly." ~Anonymous

The process of differential diagnosis has some applications to crime and intelligence analysis. Differential diagnosis in medicine often refers to a systematic rather than intuitive approach to diagnosing medical conditions. To begin, the physician considers the most common cause for a problem (a set of one or more symptoms) and will rule that out first, before going on to explore the next likely explanation, as so on, as needed, until a correct diagnosis can be made.

In crime and intelligence analysis we have defined no such systematic process. Here is an example of how we might follow this type of process unconsciously (without naming it):

We see a cluster of robberies on a map and decide could be a series, especially if the crimes occur in a low-robbery area. But we cannot stop there and create a bulletin until we run more "tests" to see if our initial "diagnosis" is correct. We may read the reports to look for similar modus operandi - suspect descriptions, weapons, victims, etc. Suppose we do so and find that the crimes seem unrelated? Often we might then ignore the cluster, since we cannot explain it by the most obvious "diagnosis." However, we may examine the "set of symptoms" further and search for more explanations. What might be the next likely explanation? Knowing your jurisdiction will help you here. Suppose we know that there are a number of bars/taverns in that area? Perhaps are next "diagnosis" would be related to the density of crime risk facilities - those that promote alcohol use. We study further to see if that explains the cluster of robberies. If we rule out that diagnosis - say the robberies are occurring at 10 AM and seem unrelated to those establishments, we then look for another cause. A recent parolee released into the community may be the next "diagnosis." The analysts then searches information to find out if this explanation is the correct "diagnosis." As we move into less obvious explanations, the analytical work often becomes more time-consuming. Intelligence information is needed to make the correct diagnosis - a gang has set up shop in the neighborhood and gang members are committing what seem like random robberies.

Often, such in-depth analysis cannot be done because staffing is insufficient and/or the information available to "diagnose" correctly is unavailable. Thus, a number of crime problems go "undiagnosed" or "misdiagnosed." In "diagnosing" crime problems sufficiently, we need both crime analysis and intelligence analysis information. Sometimes, we need collaboration. Good critical thinking is a necessity. Without a correct "diagnosis," our response to any particular crime problem is obviously less likely to be effective. That said, just like in treating disease, sometimes problems go away by themselves and it doesn't matter what the physician does. Yet we know that some problems, such as an undetected serial killer, like a dangerous virus, are crucial to catch early. Differential diagnosis can save lives.