In this case, those on the verge of poverty would also be marginal in the technical sense because a given price rise would cause them to choose to leave whereas those with more money might choose to stay because it's an easier choice.
The GP make simple and correct point - those with more money can wind-up choosing to buy something they "don't want that much" while those with less money overall money forgone things they very much want since they also need to eat.
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In this case, those on the verge of poverty would also be marginal in the technical sense because a given price rise would cause them to choose to leave whereas those with more money might choose to stay because it's an easier choice.
The GP make simple and correct point - those with more money can wind-up choosing to buy something they "don't want that much" while those with less money overall money forgone things they very much want since they also need to eat.