Lars Ericson

Tweaking ACH for FARC

ACH is a methodology which scores Inconsistency but doesn't score Consistency. At most it says that evidence is really not consistent with the outcome, without opining on whether it is consistent. https://en.wikipedia.org/wiki/Analysis_of_competing_hypotheses http://competinghypotheses.org/docs/ACH,_Step_By_Step has Credibility and Relevance scores

The Xerox ACH implementation http://www.pherson.org/PDFFiles/ACHTechnicalDescription.pdf
has Credibility and Relevance scores of Low=1/sqrt(2), Medium = 1 and High = sqrt(2). The Consistency score is Very Inconsistent = -2, Inconsistent=-1, and Neutral, Consistent and Very Consistent are 0. The Weighted Inconsistency Score is Credbility * Relevance * Consistency. So any evidence item which is not inconsistent gets a weight of 0.

For my ACH-ish model, as applied to rationales with comments supplied for forecasts, I will weight as follows. Let the forecast be F. Assign Credibility and Relevance scores of Low=1/(2*sqrt(2)), Medium = 1/sqrt(2), and High = 1. Let the Consistency score C be -1,-1/2,0,1/2,1. Let W = Credibility * Relevance. Then my ACH-ish-model weighted forecast will be W*(C*(F-50)+50), where forecasts are in range 0 to 100.

Just FYI y'all, in case you care. So far I see 74 forecasts for FARC of which 32 have rationales. My model for FARC is ACH-ish as above. The Consensus has been towards 0 on FARC except it just picked up a little. The early comments on FARC anticipated that pick-up.

2 Replies

Lars Ericson
FARC forecasting.
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Lars Ericson
Actually I think I will go with W*100*(C+1)/2 and ignore the original forecast in the formula, just looking at it as a shorthand for the text and how to view the import of the text.