By this I mean that yes, certainly, macroeconomics, the taming of boom and bust, can indeed have effects over short time periods.

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But the transplant's effects faded over time, and the cells are in such short supply that only hundreds of people have been able to get them.

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Of course, since cell phones have been in use for a relatively short time, we cannot rule out the possibility that heavy and long-term use may prove to have effects when more time has elapsed.

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Less certain, however, are aspirin's short-term effects, as well as how the balance of risks and benefits of taking the medication changes over time.

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