Data & Methodology

Methodology

Difference-in-Differences Design

The analysis compares building permits inside the MIN overlay to permits outside MIN but within the same council districts (CD3 and CD7). This within-district design controls for neighborhood-level trends, political attention, demographics, and market cycles. The only systematic difference between the two groups is MIN exposure.

Because the pre-MIN period (3.54 years) and post-MIN period (3.45 years) differ slightly in length, annualized rates provide a fairer comparison than raw counts. Only permits with confirmed unit counts of 10 or more are included in the primary causal analysis — these are the projects MIN legally regulates.

Unit Loss Estimation

The unit loss estimate uses a 0% growth counterfactual — a flat continuation of the pre-MIN permit rate with no assumed market growth. This is deliberately conservative. The 64 lost permits are multiplied by three estimators of average project size (mean, trimmed mean, median) to provide a range. The headline uses the trimmed mean (~3,000 units) to reduce the influence of a few very large projects on the estimate.

MIN Spatial Classification

Permits are classified as inside or outside MIN using a spatial join against the Philadelphia City Planning Commission’s Zoning_Overlays shapefile (downloaded from OpenDataPhilly). Each permit’s geocoded location is tested for containment within the /MIN overlay polygon.

TOC Yield Analysis

The forward-looking TOC impact uses a hybrid methodology:

• FAR-bonus zones (CMX-3/4/5/RMX-3) in MIN: 30% FAR bonus blocked by law per §14-513(5)(a)(.2). Zero additional units.
• Density-bonus zones (RM-1/CMX-1/CMX-2/CMX-2.5) in MIN: 50% density bonus is legally available, but a 0.44 DiD-adjusted behavioral deterrent is applied to projects with 10+ unit capacity. The 0.44 rate derives from the empirical finding: expected production without MIN = 28.7/yr; actual with MIN = 16.0/yr; ratio = 16.0/28.7 = 0.557; deterrent = 1 − 0.557 = 0.443.

Parcel-level capacity uses the BPN zoning rules engine with Philadelphia Zoning Code dimensional standards and Eriksen & Orlando (2022) construction cost thresholds for the cost cliff adjustment.

MIHB Revenue Comparison

Lost Housing Trust Fund revenue is estimated by multiplying the ~3,000 lost units by the MIN fee-in-lieu rate ($10,900/DU for density zones). This is conservative — the MIHB Low Income rate is $17,700/DU. The Basic Systems Repair Program comparison uses an average grant of ~$15,000 per household (program maximum: $20,000).

Limitations

• Causal identification: The DiD design assumes parallel trends would have continued absent MIN. The 0% growth counterfactual is conservative but may understate losses if the inside-MIN areas would have grown faster than the control group.
• Unit count coverage: 39% of permits have confirmed unit counts. The primary analysis uses only permits with ≥10 confirmed units. Permits without unit counts are excluded from the causal analysis but included in the broader context.
• OPA match rate: 98.9% of permit addresses matched to OPA records. The 1.1% unmatched are excluded from parcel-level analyses (zoning classification, lot size, market value).
• Confounding with tax abatement changes: The 10-year tax abatement was reduced effective January 1, 2022, and a 1% construction tax was imposed — six months before MIN took effect. The DiD design controls for this because both treatment and control groups face the same abatement rules. However, the interaction between abatement reduction and MIN is not separately identified.
• Small control group: The outside-MIN control within CD3+CD7 is smaller than the treatment group (37 vs 125 large permits pre-MIN), which increases variance in the DiD estimate.