Plot job vacancies against unemployment and a predictable curve appears

In 1944, William Beveridge argued that unfilled job vacancies and unemployment move in opposite directions: more openings, fewer jobless, and vice versa. Charting the two together over time traces a downward-sloping curve. When that curve shifts outward — the same number of vacancies now sitting alongside more unemployed workers — economists read it as a labor market growing worse at matching people to jobs.

— William Beveridge, Full Employment in a Free Society — 1944
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