Greg Mankiw wrote in National Affairs a couple days ago about the effectiveness and politicization of the stimulus. His analogy comparing the economy to a sick patient is great:

To understand the challenge government economists have faced over the past year and a half, it is useful to imagine the case of a physician trying to treat an ill patient. The patient presents herself in terrible shape; the physician has never treated a condition with symptoms quite like hers before; and the causes of the ailments are unclear. The doctor remembers reading about a similar case in medical school — and, trying to recall as much of his training as possible, he endeavors to come up with a theory as to why the patient is sick and to determine what will make her better.

In an ideal world, the doctor would run a controlled experiment: He would assemble 100 patients with similar symptoms, give 50 of them the medicine that seems most likely to work and the other 50 a placebo, and then see whether the patients on the medicine in fact improved. But the doctor does not have 100 patients — he has only one. So, based on his assessment of what is causing the patient’s troubles, and the most likely remedy, he takes a risk and administers the medicine.

The patient, however, returns a few weeks later; this time, her symptoms are worse. What, then, should the doctor conclude? He might decide that he gave the patient the wrong medicine. Or he might determine that the patient was even sicker than he originally thought, and thus that the medicine should be administered at an even higher dosage. Either conclusion is plausible, but there is no way the doctor can be sure. What he does know is that he must act before the situation gets even worse.

I think that’s a great way to understand the incredible inconclusiveness and frustrating state of evaluating the Obama stimulus package. Was the economy sicker than the doctor thought, and thus the unemployment being at 10% (higher than the 8% promised by Obama’s economic team) was due to lack of a big enough stimulus? Or do stimuli simply not work and the trillion or so dollars spent trying to revive the economy were all just an inefficient waste of money?

The second thing I particularly like about Mankiw’s piece is his focus on efficient spending that improves standard of living, rather than a boost in statistical GDP:

To look at it another way: If a person pays his neighbor $100 to dig a hole in his backyard and then fill it up again, and the neighbor hires him to do the same, government statisticians will report that the economy has created two jobs and that the gross domestic product has risen by $200. But it is unlikely that, having wasted all that time digging and filling, either person is better off — economically or otherwise. Each person’s net financial gain is zero, and all anyone has to show for the effort is a patch of fresh dirt in the backyard, which is unlikely to improve anyone’s standard of living.

Private individuals don’t usually spend their money on things they don’t want or need. So when money is kept in the hands of citizens, and transactions take place in the private sector, there is less cause to worry about inefficient spending. The same cannot always be said of government. This means that government spending designed to stimulate the economy must first be subjected to serious cost-benefit analysis, which is hard to do in a big rush. Not all government spending is created equal — and rushed spending is, in many important ways, likely to be less efficient and less useful than spending that is carefully planned.

Read the whole article here for an easy-to-read analysis of the stimulus and the economics profession in general.