R-squared?

From Conscience of a Liberal:

... Larry Summers has finally made the point I’ve been pushing for a while — that we’re at major risk of falling into a deflationary trap.

I thought it might be useful to present a bit of evidence behind that concern. The figure above plots an estimate of the output gap — the difference between actual and potential GDP, as a percentage of potential — and the change in the inflation rate. Both series are taken from the IMF WEO database, for convenience, and use data from 1980-2007.

It’s not a perfect fit — this is economics, not physics, and anyway stuff besides the output gap bounces inflation around from year to year. But still, there’s a clear correlation, driven largely but not entirely by the deep slump and disinflation of the early 1980s, and an implied slope of about 0.5 — that is, every percentage point by which real GDP fall short of potential tends to reduce the inflation rate by about half a point over the course of the year.

And right now the CBO is saying that in the absence of a policy action the average output gap will average 6.8 percent over the next two years. Do the math: if anything like the historical relationship between output and inflation holds, we’re looking at major deflation.

From the comments section:

I accept the correlation; it makes sense, but as someone who just taught a room full of freshmen about the value of data fitting, an r^2 would be nice. And perhaps a statement as to what is considered acceptable fit in economics versus physics.