Saturday, October 19, 2019

On finding the weakest link...

Last week I read and responded to a flurry of email exchanges that were prompted by Jonathan Morell circulating a think piece titled 'Can Knowledge of Evolutionary Biology and Ecology Inform Evaluation?". Putting aside the details of the subsequent discussions, many of the participants were in agreement with the idea that evaluation theory and practice could definitely benefit by more actively seeking out relevant ideas from other disciplines.

So when I was reading Tim Harford's column in this weekend's Financial Times, titled 'The weakest link in the strong Nobel winner 'I was very interested in this section:
Then there’s Prof Kremer’s O-ring Theory of Development, which demonstrates just how far one can see from that comfortable armchair. The failure of vulnerable rubber “O-rings” destroyed the Challenger space shuttle in 1986; Kremer borrowed that image for his theory, which — simply summarised — is that for many production processes, the weakest link matters.
Consider a meal at a fancy restaurant. If the ingredients are stale, or the sous-chef has the norovirus, or the chef is drunk and burns the food, or the waiter drops the meal in the diner’s lap, or the lavatories are backing up and the entire restaurant smells of sewage, it doesn’t matter what else goes right. The meal is only satisfactory if none of these things go wrong.
As you will find when you do a Google search to find out more information about the O-ring Theory of Development, you will find there is a lot more to the theory than this, much of it very relevant to evaluators.  Prof Kremer is an economist, by the way.

This quote was of interest to me because in the last week I have been having discussions with a big agency in London about how to go ahead with an evaluation of one of their complex programs. By complex, in this instance, I mean a program that is not easily decomposable into multiple parts – where it might otherwise be possible to do some form of cross-case analysis, using either observational data or experimental data. We have been talking about strategies for identifying multiple alternative causal pathways that might be at work, connecting the program's interventions with the outcomes it is interested in. I'll be reporting more on this in the near future, I hope.

But let's go right now to a position a bit further along, where an evaluation team has identified which causal pathway (s) are most valuable/plausible/relevant. In those circumstances, particularly in a large complex program, the causal pathway itself could be quite long, with many elements or segments. This in itself is not a bad thing, because the more segments there are in a causal pathway that can be examined then the more vulnerable to disproof the theory about that causal pathway is – which in principle is a good thing – especially if the theory is not disproved – it means it's a pretty good theory. But on the other hand, a causal pathway with many segments or steps pose a problem for an evaluation team, in terms of where they are going to allocate their resource-limited attention.

What I like about the paragraph from Tim Harford's column is the sensible advice that it provides to an evaluation team in this type of context. That is, look first for the weakest link in the causal pathway. Of course, that does raise a question of what we mean by the weakest link. A link may be weak in terms of its verifiability or its plausibility, or in other ways. My inclination at this point would be to focus on the weakest link in terms of plausibility. Your thoughts on this would be appreciated. How one would go about identifying such weak links would also need attention. Two obvious choices would be either to use expert judgement or different stakeholders perspectives on the question. Or probably better, a combination of both.

Postscript: I subsequently discovered some other related musings:


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