This time I am going to talk about a specific and easy to understand tool for revealing patterns in our data. It is called the Probability/Strangeness matrix, and it has been around for decades, although I’ve yet to see it used to its full potential.
The matrix is very simple. After we have investigated a case, we rate the case on a scale of 0 to 5 for both probability and strangeness. These two ratings are required to be independent – a case can be strange but improbable, it can be probable but not very strange, or any combination. What we are of course most interested in the small fraction of cases in the upper right hand corner of the matrix that are both probable and strange, and how they move on the matrix as the investigation proceeds. It’s very clear from the plot – usually done with probability on the horizontal axis and strangeness on the vertical – what is going on.
