Definition
Labor supply elasticity measures the percentage change in labor supply (hours worked or labor force participation) in response to a one-percent change in the net wage or income. The concept has two distinct margins: the extensive margin (the decision whether to work at all, i.e., labor force participation) and the intensive margin (the decision of how many hours to work conditional on participation). The extensive and intensive margins respond differently to wage and income incentives, and their relative magnitudes determine the effectiveness of transfer programs and tax policies designed to encourage work.
Key Ideas
- Extensive vs. intensive margin: The extensive-margin elasticity measures how participation rates change with the net wage (a 1% increase in the net wage raises participation by εe percent). The intensive-margin elasticity measures how hours conditional on working change (εi). For low-income workers, the extensive margin typically dominates: the participation decision (work vs. not work) is more responsive to incentives than the hours decision.
- EITC and the extensive margin: The Earned Income Tax Credit (EITC) generates large extensive-margin labor supply effects — the phase-in subsidy substantially increases employment rates among single mothers and other target groups. Estimated extensive-margin elasticities for single mothers range from 0.5 to 1.5 (Eissa and Liebman 1996; Meyer and Rosenbaum 2001). This is one of the largest and most credibly identified labor supply responses in the empirical literature.
- Near-zero intensive margin for EITC: Despite large participation effects, the EITC generates near-zero intensive-margin effects. Workers do not concentrate their hours at the budget-constraint kink points (phase-in/plateau boundary) as standard theory predicts. Chetty and Saez (2009) show that Information Frictions — workers' failure to understand the EITC budget constraint — largely explain this non-response: when workers are informed of the credit structure, bunching at kink points increases significantly.
- Compensated vs. uncompensated elasticities: The uncompensated (Marshallian) elasticity combines substitution and income effects; the compensated (Hicksian) elasticity holds utility constant. For welfare analysis of tax policy, the compensated elasticity is the relevant object; for predicting revenue and behavioral effects, the uncompensated elasticity is needed.
- Heterogeneity: Labor supply elasticities vary substantially across demographic groups. Single mothers, secondary earners, and workers near the participation margin exhibit the highest extensive-margin elasticities. Prime-age male workers traditionally show low intensive-margin elasticities (≈0.1–0.2).
- Disability Insurance (DI) context: The earnings elasticity with respect to DI benefit generosity (intensive margin on the earnings side) is approximately −$0.20 per $1 of benefit — a pure income effect, not a substitution effect, as established by the Regression Kink Design at Average Indexed Monthly Earnings (AIME) bend points. See Regression Kink Design and Optimal Social Insurance.
Why It Matters
- Tax and transfer design: The extensive-margin dominance for low-income workers is the key justification for phase-in subsidies (EITC, negative income tax structures): they encourage participation without creating large hours distortions.
- DI work incentives: Understanding the income vs. substitution effect decomposition of DI's labor supply response determines whether DI-induced work reduction is welfare-reducing (substitution) or merely a transfer (income). Gelber, Moore, and Strand (2016) establish the ≈$0.20 reduction is a pure income effect. See Causal Effects of DI Receipt.
- Policy evaluation: Any policy that changes the net wage schedule (tax reform, EITC expansion, minimum wage increase, DI benefit cut) affects labor supply through both margins; the elasticities determine the magnitudes.
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