There have been many tests of the convergence hypothesis yielding many different estimates of β (the speed of convergence). Narrative reviews of the convergence literature hint at possible reasons for the study-to-study variation in the value of β, but such reviews are selective and informal....

Combining concrete policy-oriented modeling strategies of World War II with what was received as traditional neoclassical theory, in 1956 Robert Solow constructed a simple, clean, and smooth-functioning "design" model that served many different purposes. As a working object it enabled...