The word function has different meanings. For example, it can describe what something is used for (e.g., the function of the brakes is to slow or stop the car), it can describe a formal event (e.g., a charitable function), or it can describe dependency of one thing on another (e.g., weight is a function of height). This last example gets closest to another use of “function” as a mathematical term.
The woman who taught me Algebra II, Trigonometry and Calculus used to explain functions using a Coke-machine analogy. When you input a value by pressing the Coke button on the machine, the machine processes that input (executes the function) and spits out the output value in the form of a can of Coke. The function is fixed, such that every time you hit the Coke button a can of Coke comes out. If we hit the Coke button and were as likely to get a can of Coke as we were a can of Sprite or Dr. Pepper, we wouldn’t have a function. There can be more than one way to get the same result (i.e., there can be more than one Coke button on the machine), but when we press a given button we always know what we’re going to get.
In health care, an important question becomes: What function defines the relationship between health care spending and health outcomes? Is the relationship linear or not? If it’s linear, then spending more and more money on health care should produce more and more improvements in health at a constant per dollar rate. Since none of us will live forever, we ought to know that there are clearly diminishing returns on our health care dollar, and that the relationship is no longer linear, but curvilinear. That is, at some point, spending more money on health care produces fewer gains in health–in fact, it may even harm health at some point.
But let’s not worry about that curved part of the line just yet. In the early going, is a dollar spent on health care equally beneficial to health? Not according to a recent Health Affairs article by Michael Rothberg and colleagues. Instead, they find that there is actually very little correlation between spending and outcomes. In some cases, spending more might be beneficial, and in other cases, spending more might just be completely wasteful. That has little to do with how much is being spent and most everything to do with understanding which treatments work and which don’t. Thus, the need for more comparative effectiveness research (CER), as I’ve harped on plenty of times before.
Without CER, we put our money in the health care Coke machine, press a button and hope to get better. Sometimes we get what we’re after. Other times, nothing comes out at all. We’re making a good investment in the first case, and a terrible waste in the second. If our goal is to buy as much good health as possible with the money in our pocket, we would do well to figure out which buttons on the machine don’t work, and make sure that after we feed in our dollar, we never press those buttons. That’s the potential of CER in health care reform: Making sure we stop paying for things that don’t work.