July 12, 2012

Impact, Outcome and INUS causes

Interesting discussion on the Outcome Mapping mailing list - here is something I just posted. This part of the discussion was about whether Outcome Mapping, which focusses on the contribution of an intervention to a development result rather than on deciding whether a result can be (entirely) attributed to an intervention.

I agree that on the one hand both OM (and by extension, it seems Outcome Harvesting) as well as Impact Evaluation are both indeed involved in making causal claims. And on the other hand perhaps OM is just a bit more realistic about what kind of causal claims can be realistically made.

The recent DfID/Stern report on Broadening the range of designs and methods for impact evaluations” (http://www.dfid.gov.uk/r4d/Output/189575/Default.aspx, p 41) nicely goes back to Mackie (1974) and INUS causes - an insufficient but necessary part of a condition that is itself unnecessary but sufficient for the occurence of the event - which is it seems often what we really mean when we talk about causes in real life.

So we can say some intervention is a contributory cause for some result if the intervention was a necessary part of a whole context full of other things which were happening; and this whole package of things was enough to make the result happen, but it might have happened other ways too. I guess this is roughly what OM means when it talks about contribution? If so, good. And if Impact Evaluation thinks it is really dealing with necessary & sufficient causation between intervention and result it is living in totally cloud-cuckoo land.

It isn’t really enough to just use the words impact” or outcome” with a certain kind of tension in our voices and hope that people understand which kind of cause we are thinking about. In my view the Stern report goes a long way to unpacking some of these things and is a worthwhile read. And the very title of that report seems to suggest that we should feel free to use the word impact” for what OM claims, because it is (perhaps unfortunately, seeing as how we don’t have agreement on these things at the moment) more important to spell out each time what kind of claim we are making rather than just hope that our use of certain code-words will be understood by all - they aren’t.


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