Wednesday, June 17, 2009

Causal Bias

As humans we naturally look for a cause for every event even if none exists. A gambler will attribute a winning streak to "being hot" or "beginners luck" when in reality randomness alone prevails.

You should be aware of this tendency in problem solving also. We naturally want to find a concrete reason for every event. Take the rudimentary root cause analysis here. Our first instinct is to look for the cause of a rupture disk failure as an overpressure in the reactor. After all, isn't that what the rupture disk is there for? This can quickly lead down the path of investigating the reaction conditions and potentially getting involved in a costly solution.

Another explanation is just that the disk failed randomly. (Insert Link to Drunkard's Walk) Perhaps it was installed incorrectly? The installation can be considered random, particularly if someone who doesn't routinely do the task was involved. Maybe the disk was an outlier (not really random problem) and failed at a much lower pressure than design pressure?

What evidence do you to support either route? Is it simple evidence (like pressure readings from a data logging transducer) or the opinion of an expert who has had bad experience with runaway reactions in the past? The strength of the Apollo Root cause approach is that it helps you to explore many different pathways, but most critically you need evidence to support whatever pathway you go down.

Perhaps you have evidence for both. In the future I'll explore ways to weigh evidence in order to choose the proper route to explore.

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