Analysis of competing hypotheses¹ (ACH) is a process whereby you identify a set of hypotheses, systematically evaluate data that is consistent and inconsistent with each hypothesis, and reject the hypotheses that contain too much inconsistent data.
ACH is a tool to aid judgment on important issues which require careful weighing of alternative explanations or conclusions. It helps an analyst to overcome, or at least minimize, some of the cognitive limitations that make intelligence analysis so difficult.
ACH is an eight-step procedure which is an effective, proven process to help analysts avoid common pitfalls. It is particularly appropriate for complex issues when analysts want to leave an audit trail to demonstrate what they considered and how they arrived at their judgement.
¹ Heuer, Richards J.Psychology of Intelligence Analysis. 1st ed.Vol. Chapter 8—Central Intelligence Agency, 2007.https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/books-and-monographs/psychology-of-intelligence-analysis/art11.html.