Week 3 · Final research publication
Back Bay leads on price. Hanover leads on growth.
The shared 80-month protocol produces three distinct conclusions: Back Bay has the higher forecast index level and modest projected momentum; Hanover has the stronger observed trajectory and lower selected-model error.
Back Bay 02116Hanover 03755N = 80 per city44 backtests per city
Olu (Tim) Daramola
ChrionML® AI Labs · 64-City Intelligence Program
Published: 9 October 2026Research article: Week 3Housing type: Condo/co-op
Abstract
We analyzed 80 monthly condo/co-op Zillow Home Value Index observations for Back Bay 02116 and Hanover 03755 from January 2020 through August 2026. Five interpretable forecasting candidates were evaluated across 44 expanding-window, one-month-ahead backtests per city. Drift minimized mean absolute error in Back Bay; Last Value performed best in Hanover. The September 2026 forecasts are $1,300,581 and $521,201, respectively. Hanover nevertheless recorded substantially stronger cumulative observed growth and lower selected-model MAE. The findings show why price level, market trajectory and predictive accuracy should be reported separately. Published 9 October 2026.
Research goal
To compare the next-month condo/co-op index outlook for two Northeast ZIP codes while testing whether a consistent model-selection protocol identifies different locally appropriate forecasting rules.
Methods summary
ChrionML® manually located the condo/co-op series on each Zillow market page, transcribed the monthly history into analysis-ready datasets, and verified date continuity, duplicate dates, missing values and nonpositive observations. Last Value, 12-month Seasonal Naive, Drift, 36-month Linear Trend and Holt Damped Trend were evaluated chronologically. The lowest-MAE candidate was selected independently for each city without look-ahead information.
Principal finding
One matchup, three legitimate leaders.
Back Bay leads forecast price. Hanover leads cumulative growth and selected-model accuracy. None of these measures alone determines affordability, investment quality or market superiority.
$1.301MBack Bay forecast
$521KHanover forecast
+10.77%Back Bay since 2020
+57.50%Hanover since 2020
What the evidence shows
Four findings measured under one repeatable protocol.
Forecast price
Back Bay leads the price board
The September estimates are $1,300,581 for Back Bay and $521,201 for Hanover—a 2.50× difference in modeled index level.
Momentum
Back Bay holds a modest month-ahead edge
Drift implies +0.12% for Back Bay; Hanover’s Last Value selection produces a flat point estimate.
Trajectory
Hanover leads cumulative appreciation
Hanover rose 57.50% since January 2020 versus 10.77% for Back Bay across the observed condo/co-op histories.
Model selection
Local evidence again rejects one universal winner
Drift narrowly improves on Last Value in Back Bay ($2,833 vs $2,898 MAE); Last Value is selected in Hanover at $2,312 MAE.
Data availability and provenance
Zillow publishes the underlying ZHVI histories by geography and housing type. The headline value displayed near the top of a Zillow market page may describe a different housing category. For this study, ChrionML® used the monthly condo/co-op series shown within each page, constructed the datasets, performed QA, evaluated the models, and authored the findings. Zillow did not produce, review or endorse the forecasts.
Limitations
ZHVI is an index rather than a property appraisal. The study uses ZIP-level monthly histories and a one-month horizon; it does not directly model property characteristics, inventory, mortgage rates, policy changes or local shocks. Prediction intervals quantify historical residual uncertainty, not every possible future outcome.
Interpretation boundary. “Winner” on the price board means only the higher next-month forecast index level. Growth leadership and forecasting accuracy are reported separately.
References
- Zillow. Home Value Index market history for Boston, Massachusetts 02116; condo/co-op view.
- Zillow. Home Value Index market history for Hanover, New Hampshire 03755; condo/co-op view.
- ChrionML® AI Labs. Research Methodology, version 1.0.
