Plumbing and indirect causation
In both my price theory textbook (webbed) and Hidden Order, I point out that one cannot safely assume that changing one thing in a system leaves everything else unchanged; the context there is the effect of changing one element in a transaction, such as the price, the terms the good is sold at, or the quality of the good, on the other elements. In order to figure out what will happen, you need to understand the causal links. My four examples can be found in Chapter 2, under the subtitle "Four Wrong Answers."
I recently encountered another example of the same principle, in a rather different context. Our shower had been persistently dripping. After the tenth time my wife reminded me of the problem, I decided to do something about it. My conjecture was that the valve needed to be replaced, adjusted, or cleaned out, so I attempted to disassemble the mechanism to get at the valve.
I was unsuccessful in my attempt, but managed, in the process, to fix not only that problem, without knowing I was doing it, but two others as well.
How did I work that miracle? I succeeded in disassembling the shower head,and discovered that its filter was clogged. Cleaning that out was easy. I reassembled it, making a mental note that we still had to do something about the dripping. Had I thought more about it, I would have made a further mental note that while doing so, perhaps by hiring a plumber, we might also try to do something about the low water pressure and how long it took the shower to heat up.
If I had, I would have been wrong—because I had just fixed all three problems. With the filter cleaned, the water could get through the shower head, so the low water pressure problem disappeared. As I should have expected, but didn't, the problem of heating up the water disappeared too. With the water free to go through the pipe and shower head much faster than before, it took much less time to empty out the cold water in the hot water pipe, so instead of waiting for a minute or two to start taking a shower, it now took only ten or fifteen seconds.
The dripping stopped too. I conclude that it wasn't a problem with the valve at all. Presumably, the stopped up filter meant that the shower head filled up with water, and that was what was dripping.
A nice lesson in interconnected causation.
I had thought of using this as a lead-in to a discussion of what might go wrong with current health care reform, due to the interrelated causation of that much more complicated system, but I think I will leave that to a later post.