An article in the Wall Street Journal in 2012 discussing Okun’s law observes: “The law has been unreliable lately. Under [Okun’s law], it would take growth between 4% and 5% to explain the improvements in unemployment in the past year—much more than the recovery has actually delivered.”

a. What is Okun’s law?

b. What explanations have economists offered for the unreliability of Okun’s law after the 2007–2009 recession?