Okun's Law

I've been reading N. Gregory Mankiw's intermediate textbook for fun. It's hard to believe that this is an intermediate text. My sales rep, Richard Rosenlof, Worth Publishing, gave me an examination copy a month ago. I have read this text every chance I could. In the chapter on Economic Fluctuations, he shows a scatter graph of the change in GDP related to the change in unemployment. This relationship is known as Okun's Law. This law observes that a 1% change in the unemployment will change GDP by 2%. The graph (click to enlarge) is from the US Department of Commerce and makes the point.