Week 1 · Final research publication
Boston leads on value. Providence leads on momentum.
A controlled comparison of two ZIP-level condo/co-op series using the same 80-month sample length, candidate models and chronological evaluation rules.
Boston 02114Providence 02903N = 80 per city44 backtests per city
Olu (Tim) Daramola
ChrionML® AI Labs · 64-City Intelligence Program
Published: 25 September 2026Research article: Week 1Housing type: Condo/co-op
Abstract
We compared ZIP-level condo/co-op Home Value Index histories for Boston 02114 and Providence 02903 using 80 monthly observations per city. Five interpretable forecasting candidates were evaluated across 44 expanding-window, one-month-ahead backtests. Drift produced the lowest mean absolute error in both markets. Boston retained the higher modeled price level, whereas Providence showed stronger projected monthly momentum and substantially greater observed appreciation since January 2020. Published 25 September 2026.
Research goal
To test whether a common short-horizon forecasting protocol can distinguish market value, projected momentum and historical trajectory without collapsing them into a single, potentially misleading definition of a market “winner.”
Methods summary
Candidate models included Last Value, 12-month Seasonal Naive, Drift, 36-month Linear Trend and Holt Damped Trend. Models were trained chronologically and selected independently for each city using the lowest one-step-ahead mean absolute error. No future observation was available to a model during backtesting.
Primary finding
Price level and momentum answer different questions.
Boston’s selected model forecasts the higher next-month condo value. Providence’s selected model produces the stronger percentage change and its observed trajectory since January 2020 is substantially steeper.
$779KBoston forecast
$438KProvidence forecast
+0.06%Boston momentum
+0.44%Providence momentum
What the evidence shows
Market value, projected change and historical trajectory are reported separately.
Value
Boston retains the higher forecast value
The September 2026 estimate is $779,306 for Boston versus $438,308 for Providence—a 1.78× ratio that describes market level, not investment quality.
Momentum
Providence leads the month-ahead projection
The selected models imply +0.44% for Providence versus +0.06% for Boston, a 0.38 percentage-point difference.
Trajectory
Providence has appreciated faster since 2020
Observed cumulative change is approximately +53.2% for Providence and +4.9% for Boston over the research window.
Model selection
Drift wins both local backtests
Drift improves mean absolute error by 4.4% in Boston and 24.2% in Providence versus the last-value baseline.
Data availability and provenance
Zillow publishes the underlying Home Value Index histories by geography and housing type. ChrionML® identified the ZIP-level condo/co-op series, compiled the displayed monthly observations into research datasets, checked dates and values, and independently produced the forecasts, model comparisons and visualizations.
Limitations
The analysis uses a market index rather than property-level transactions; it does not directly model interest rates, inventory, regulation or local shocks. Model selection reflects historical out-of-sample error and does not guarantee future accuracy.
Interpretation boundary. These results compare modeled market-level indices. They do not measure individual property value, affordability, rent yield, neighborhood quality or expected investment return.
References
- Zillow. Home Value Index for Boston, Massachusetts 02114, condo/co-op series.
- Zillow. Home Value Index for Providence, Rhode Island 02903, condo/co-op series.
- ChrionML® AI Labs. Research Methodology, version 1.0.
