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Equation 10 · Part 2 · The Jagged Frontier Fallacy: Deconstructing Harvard's Canonical AI Productivity Study

Symbol s

Δln⁡TFP≈∑s∈Aαs⋅πs,\Delta \ln \text{TFP} \approx \sum_{s \in \mathcal{A}} \alpha_s \cdot \pi_s,
ss

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s appears in the bound of this sum. The bound states where the repeated operation starts, ends, or which values it includes.

The passage around this formula

where each task y(s) can be performed by labor or by an automated system if that task falls within the feasible automated set A\mathcal{A} . Under Hulten’s theorem, the first-order aggregate TFP cost savings from automating a subset of tasks is bounded by the expenditure share of the automated tasks multiplied by the average unit cost reduction: Δln⁡TFP≈∑s∈Aαs⋅πs\Delta \ln \text{TFP} \approx \sum_{s \in \mathcal{A}} \alpha_s \cdot \pi_s. where αs\alpha_s is the baseline economic share of task s and πs\pi_s = cL(s)−cA(s)cL(s)\frac{c_L(s) - c_A(s)}{c_L(s)} represents the proportional cost reduction achieved on that task [ 2 ] .

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