Intelligence Analysis Skills: An Example of the Analysis of Competing Hypotheses Method 

The last hypothesis ends up being the "right" one because all of the evidence is consistent and there is no inconsistent evidence. Generally, with ACH we don’t dump/eliminate hypotheses. We can simplify the matrix by getting rid of evidence (rows) that are consistent with all hypotheses because those rows don’t contribute any actual information to our comparison of hypotheses. We keep the hypotheses all the way through to the end, including the write up and reporting. The flour example is a useful illustration but in reality, ACH matrixes rarely reduce down quite this neatly with one hypothesis being a clear “winner” and the others being excluded by decisive evidence. Often the matrix yields a couple possibilities that we rank in terms of likelihood with the strongest hypotheses having the least disconfirming evidence. When we report results for ACH we say something like, I considered 4 hypotheses, the flour being bad was found to be most consistent with the evidence. The other three… were judged to be less likely or very unlikely.