The word “shortage” says more than you might realize. A shortage is when there is too little of something to clear the market at the going price. Thus, a shortage is a sign that the price is too low to clear the market. Usually, this is a temporary situation: the price adjusts upward and people quit complaining about a shortage and start complaining about high prices instead.  

There are two general situations in which a price might be too low to clear the market for a long period of time. One case is when the government imposes a price ceiling. For example, rent control leads over time to a chronic shortage of apartments.

The other general situation in which a price is chronically too low to clear the market is when there is only one big buyer or only a few big buyers in the relevant market. Having only one buyer is called monopsony. Having only a few buyers is called oligopsony. 

In any local commuting area, there are typically only a few hospitals, that account for a large share of all nursing employment–particularly for the higher-skill, higher-paid nursing jobs. Because each hospital is big enough to affect the wage in the local labor market, it worries about driving up the wage of nurses by hiring too many.  That is, the cost of the last nurse a hospital hires is not just the wage of that one nurse, but also the cost of the rise in the wage to all the other nurses it employs due to that extra hiring.

In other words, the hospital might be willing to pay a little extra to get one more nurse who is a little more reluctant to come back into the labor force, say, except that paying that higher wage to the one nurse would force it to pay more to all of its other nurses. 

Why doesn’t the same logic cause a doctor shortage? It is because doctors operate in a national labor market. Doctors make enough money that it is worthwhile for them to consider moving to other cities at some distance in order to take advantage of a modest percentage difference in pay. By contrast, nurses are often secondary earners in their families and so tied to one commuting area, or even when they are free agents,they make little enough money that the cost of moving to a whole new region to make a few percent more doesn’t seem very attractive.

Someone might object to my account of where chronic nursing shortages come from by saying it is a problem of too few spots available in programs that train nurses. Too few spots in programs training nurses would indeed reduce the supply of nurses, but should lead to complaints about nurses being expensive rather than complaints about a shortage of nurses. Yet for some reason, there are a lot more complaints about nurse “shortages” than about how expensive nurses are.