What Shifts Labor Supply

A labor supply curve shows how many hours or workers are offered at each possible wage. It slopes upward because higher wages pull more people into a job. The curve itself shifts right when, at the very same wage, more workers suddenly show up: a wave of immigration into town, a new training program that qualifies more people for the job, safer or more pleasant working conditions, or a drop in the pay of competing jobs that pushes workers toward this one. It shifts left for the reverse reasons: workers leave, training dries up, conditions worsen, or a nearby job starts paying better and pulls workers away.

The small-town highway example ties this together. Once the highway connects the town to a city, workers who used to have only local options can now commute or move for city jobs. That outside alternative makes local workers less willing to work at the old wage, so local labor supply shifts left and the equilibrium wage should rise, not fall, unless the highway also makes it easy for outside workers to commute in and take local jobs, which shifts supply right and pushes the wage down. The direction depends on which flow of workers dominates.

This sits next to labor demand, which shifts with product demand, productivity, and the price of other inputs. When supply and demand both rise, quantity of labor rises for certain, but the wage could go up, down, or stay the same depending on which shift is bigger. Keeping supply shifts and demand shifts straight, and never confusing either with a simple movement along a curve, is what makes these graphs readable instead of guesswork.