Posted by: tristar3research | March 12, 2009

ACH: This is cool for analytical types…

Wow: Tim van Gelder has some really good stuff on his blog- and anyone with complex problem analysis should take a week to go through all the tools that can be applied to complexity analysis from his insights-JMHO.

The “Analysis of Competing Hypotheses” method, or ACH, is one of the most important tools on the intelligence analyst’s bench. It is a procedure for determining which of a range of hypotheses is most likely to be true, given the available evidence. At its heart is a matrix, wherein hypotheses are listed across the top, and items of evidence are listed down the left side. There is then a square or cell in the matrix corresponding to every hypothesis/evidence pair, and in that square one indicates whether the item of evidence is (in)consistent or neutral with the hypothesis. For more information on ACH, see * the classic chapter by Richards Heuer * This brief overview (pdf file) of ACH compared with argument mapping (AM). Some of the points made below are presaged in the overview. ACH is based on some fundamental insights: * The network of relationships between items of evidence and hypothesis is “many-many”. That is, one piece of evidence can bear, one way or another, on many hypotheses, and an hypothesis is generally considered in the light of a number of pieces of evidence. The ACH matrix is an obvious and natural way to accommodate this web of relationships. * At least in many situations, structured thinking techniques yield better results than informal or intuitive “pondering”. The ACH imposes a strong structure on hypothesis testing. * Structured techniques are even more effective when making use of suitable external (i.e., outside the head or “on paper) representations. Thus long division in the head is hard; on paper, following a standard procedure, it is easy. The ACH matrix is an external representation aiding hypothesis testing. * When making informal or qualitative judgements, it is usually better to use coarse schemes such as consistent/neutral/inconsistent rather than more elaborate and precise schemes such as numerical consistency ratings. Nevertheless, in my experience using ACH, difficulties of various sorts rapidly arise; and as the expenditures of mental effort involved in struggling with those difficulties mount up, alternatives, such as “muddling through” without the use of a tool such as ACH, or using some other tool such as argument mapping, look increasingly attractive.


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