Why do economists disagree?

The New York Times asks this question.

Let’s leave aside the merits of these arguments and ask a question so basic it will sound naïve: Why do economists argue at all? Given that Fed members and economists are looking at the same data, and given the reams of evidence accumulated over decades — not to mention a few centuries of great minds, great theories and thick books that preceded this crisis — why isn’t a right answer self-evident?

George Bernard Shaw once said, “If all economists were laid end to end they would not reach a conclusion.” How come? What prevents economics from yielding answers the way that physics, chemistry and biology do?

and

To explain the case for humility in economics, Mr. [Robert] Solow said, look no further than the stimulus bill: “It has run its course over the past year and a half, but it is not an isolated event. One thousand other things were happening that had an effect on employment and real G.D.P.,” a measure of a nation’s total output adjusted for changes in prices. “You want to trace the effect of one of a very large number of significant causal effects, and that’s a very hard thing to do.”

That the world doesn’t offer up clean economic experiments is a common refrain in the discipline, said Gary Becker, a Nobelist at the University of Chicago. There have been endless studies on every tax change in the modern history of the republic, Mr. Becker said, from Kennedy to George W. Bush, and arguments about the wisdom and aftereffects of each. It’s not just that there is so little clear signal amid so much noise. It’s that many economists have a unique idea of what signal to listen to and what priority it deserves.

In other words, the world is really, really complicated. And it is complicated because of people,

But economics will forever have to contend with the biggest X factor of all: people. As Mr. Solow notes, you feed people poison, and they die. But feed them a subsidy and there is no telling what will happen. Some will use it wisely, others perversely and some a mix of both.

But you shouldn't over play the disagreement card. There are many things on which economists do agree.

This is not to suggest that economics is a total free-for-all, lacking a broad consensus on any subject. Polls of economists have found near unanimity on topics like tariffs and import quotas (bad), centralized economies (very bad) and flexible, floating exchange rates (very good).

I would suggest however that agreement is more likely on the microeconomic side than on the macroeconomic of the discipline.