Shift-Share Analysis
Also known as: Shift-Share Decomposition, SSA, Esteban-Marquillas Shift-Share, Regional Shift-Share
Shift-share analysis is a descriptive technique that decomposes the change in a regional variable — most often sectoral employment — into three additive components: the part attributable to overall national growth, the part attributable to the region's industry mix, and the part attributable to the region's own competitive performance. Formalized by Edgar Dunn in 1960, it answers whether a region grew because the national economy grew, because it specializes in fast-growing industries, or because its industries outperformed (or underperformed) their national counterparts.
Key highlights
- Exact additive identity with three economically meaningful components and no residual, making results easy to communicate.
- Minimal data requirements — sectoral counts at two time points for a region and a benchmark — so it is inexpensive and broadly applicable.
- Separates the influence of national trends and industrial composition from genuinely local performance.
- Serves as an intuitive descriptive benchmark and a stepping stone to more formal regional models and causal designs.
Intuition
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How it works
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When to use it
Use shift-share analysis as a first descriptive pass when comparing the growth of a region (or any sub-unit) against a reference area and you want to separate macroeconomic, structural, and local-competitiveness contributions. It requires only sectoral counts at two points in time for the region and the benchmark, making it cheap and widely applicable in regional economics, labor-market studies, and industry analysis. It is a descriptive accounting decomposition, not a causal model: the competitive-share residual absorbs everything not explained by national trends and industry mix, so it should not be read as a clean estimate of policy effects. For causal identification of local labor-demand shocks, the related shift-share (Bartik) instrumental-variables approach is used instead.
Strengths & limitations
- Exact additive identity with three economically meaningful components and no residual, making results easy to communicate.
- Minimal data requirements — sectoral counts at two time points for a region and a benchmark — so it is inexpensive and broadly applicable.
- Separates the influence of national trends and industrial composition from genuinely local performance.
- Serves as an intuitive descriptive benchmark and a stepping stone to more formal regional models and causal designs.
- Purely descriptive: the competitive-share component is a residual that mixes all unexplained factors and is not a causal estimate.
- Results depend on the chosen base year, sectoral aggregation, and the start-versus-end period weighting (which classic component carries known weighting biases).
- The classic three-way split confounds the industry-mix and competitive effects when a region is specialized; the Esteban-Marquillas reformulation addresses this.
- It is a static comparison of two endpoints and ignores the path and timing of change between them.
Common pitfalls
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Applications
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Frequently asked
What is the difference between shift-share analysis and the shift-share (Bartik) instrument?
Classic shift-share analysis is a descriptive accounting decomposition that splits observed regional growth into national, industry-mix, and competitive components. The shift-share or Bartik instrument reuses the same national-growth-times-local-industry-shares construction, but as an instrumental variable to identify the causal effect of local labor-demand shocks in a regression, leveraging variation in industry composition as exogenous. One describes; the other identifies a causal parameter.
Why does the competitive-share component cause interpretation problems?
The competitive (differential) share is computed as a residual — everything in regional growth not explained by national trends and industry mix. It therefore absorbs genuine local competitiveness together with measurement error, data classification artifacts, and any omitted structural factor. Esteban-Marquillas (1972) showed it is also entangled with specialization, and his reformulation adds an allocation effect to separate 'competitive because specialized in the right industries' from 'competitive across the board.'
Does it matter which year's weights are used?
Yes. The classic decomposition applies base-year employment as weights, which makes the components sensitive to the choice of start year and can introduce weighting bias when sectoral structure shifts substantially over the interval. Dynamic and average-weighted variants recompute the decomposition over sub-periods or use symmetric weights to reduce this dependence, analogous to the choice of reference structure in other decomposition methods.
Sources
- 1.Dunn, E. S. (1960). A statistical and analytical technique for regional analysis. Papers of the Regional Science Association, 6(1), 97–112.
- 2.Esteban-Marquillas, J. M. (1972). A reinterpretation of shift-share analysis. Regional and Urban Economics, 2(3), 249–255.
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ScholarGate. (2026, June 22). Shift-Share Analysis. ScholarGate. https://scholargate.app/economics/shift-share-analysis