I don't see anything in the article about the extent to which this effect has been observed in the real world. Is it another example of economists assuming that people are idealised rational actors (who would prefer a 1.6x coffee bean premium to a 2x, to take the example in the article), or is there some hard evidence that it explains the real behaviour of real people?
They give 3 examples at the end: "The effect has been studied as it applies to illegal drugs and it has been shown that the potency of marijuana increased in response to higher enforcement budgets,[2] and there was a similar effect for alcohol in the U.S. during Prohibition.[3] This effect is called Iron law of prohibition or Cardinal rule of prohibition. Another example is that Australians drink higher-quality Calif…
To clarify: I just don't see where the evidence for any of these claims is accessible. Four of the six references don't appear to be available on-line. Of the two that are, one is a brief summary that leads to a paywalled FT article that I can't read, and the other is a ~200 pdf economics textbook.
I'm happy to accept that a price differential changes when a constant is added to both prices. But I do question whether people in the real world will switch to a different type of coffee bean because the differential goes from x2 to x1.6. And I wanted to know more about the real-world circumstances in which it had been observed.
I might be pursuaded that the market for illegal drugs/alcohol could exhibit this effect, but it would be interesting to know how how, given that illegal products are probably going to be subject to other effects not shared by legal products, biases and selectivities were compensated for.
Edit: Made first paragraph clearer.