Research
Research
I use structural models and applied econometrics to study anticipation, spatial adjustment, and the returns to technology in education. I’m currently branching into different fields within industrial organization.
Working Papers
Working paper · 2026
Before the Factory Opens: Anticipation and Spatial Adjustment to Announced and Delayed Local Shocks
How much do people move before a large employer actually arrives? I develop a continuous-time spatial mean field game, built on coupled Hamilton–Jacobi–Bellman and Kolmogorov forward equations, to study anticipatory relocation around Intel’s announced Ohio semiconductor investment. The model is calibrated through an exact discrete inverse equilibrium to 969,829 worker residences from Census LODES, together with BLS QCEW data and publicly announced project employment and pay. The agents stand for the region’s whole resident labor force, in every industry, not only the people who might take a job at the plant. Roughly 46.7% of the eventual model-implied spatial adjustment occurs before the initially expected opening date, and later information revisions about project delays generate a partial reversal. Extending the model to two-dimensional geography reduces predicted reallocation by about 16% while leaving the timing result nearly unchanged.
Data & Methods
| Source | What it provides |
|---|---|
| Census LODES | Residence locations of 969,829 workers in all industries (the full resident labor force) |
| BLS QCEW | County employment and wage data |
| Project announcements | Announced employment and pay for Intel’s Ohio site |
Methods: Continuous-time spatial mean field game (coupled HJB–KFE system); exact discrete inverse-equilibrium calibration; one- and two-dimensional geography; numerical and structural robustness checks.
Code highlights
Calibrating the baseline so 2021 residences are an exact equilibrium
# Exact baseline: detailed balance at each cell face gives the value gap
# that holds the 2021 LODES distribution perfectly still.
dp = p[1:] - p[:-1]
V[1:] = np.cumsum(m0.c * D * dp / np.minimum(p[:-1], p[1:]))
V -= p @ V
a = drift(V, g, m0)
Q = controlled_Q(a, diffusion_Q(g, m0), g)
# Back out the baseline amenity b from the stationary HJB.
F = m0.kappa * (density(p, g) + m0.eps) ** m0.gamma
b = m0.rho * V - Q @ V + F + cost(a, m0)Solving for the equilibrium transition
# Mean field game fixed point: iterate HJB backward and KFE forward
# until the population path workers expect is the one they create.
for _ in range(m.dyn_max):
V, A, maxh = backward(pp) # choices, given where everyone will be
br, maxk = forward(A) # where everyone ends up, given those choices
fp = float(np.max(np.abs(br - pp)))
if fp < m.dyn_tol:
break
pp = (1 - m.dyn_relax) * pp + m.dyn_relax * br
pp[0] = p0// replication code → github.com/harperpstephens/BeforeTheFactoryOpens1023
Work in progress
Time, Tools, Technology: Identifying the Educational Returns to Technology Use
This paper extends my honors thesis to identify which specific devices, activities, and settings are associated with differences in student achievement in the 2018 Programme for International Student Assessment (PISA). Estimates are combined across PISA’s multiply imputed datasets using Rubin’s Rules, and the robustness procedures developed in the thesis are carried forward.
Data & Methods
| Source | What it provides |
|---|---|
| PISA 2018 | Student achievement and technology-use measures across devices, activities, and settings |
Methods: Estimates combined across multiply imputed datasets with Rubin’s Rules; robustness procedures carried forward from the honors thesis.
// code → github.com/harperpstephens
Manuscript available soon.
Honors Thesis
Honors thesis · University of Louisville · 2026
Educational Technology and Cognition: PISA 2018 Evidence on Technology Use and Student Performance
Using the 2018 PISA data, this thesis examines how the ways students use educational technology relate to achievement in mathematics, reading, and science. I construct a cross-country sample that accounts for differences across assessment booklets and excludes countries with insufficient observations, estimate multivariate regression models and marginal effects conditional on external controls, and test robustness with variance inflation factor diagnostics. Home technology is the strongest statistically significant technology-related predictor of achievement, socioeconomic status accounts for a substantial share of the observed relationship, and the associations differ across subjects.
Data & Methods
| Source | What it provides |
|---|---|
| PISA 2018 | Cross-country student achievement in mathematics, reading, and science, plus technology-use measures |
Methods: Booklet-adjusted cross-country sample; multivariate regression with marginal effects and external controls; variance inflation factor diagnostics and robustness checks.
// code → github.com/harperpstephens
Slides from talks on this work are collected on the Presentations page.