Every ZIP, base, city and college is scored by how many standard deviations its investment opportunity sits from the mean. A market at +3σ is a statistical extreme — a "crazy value" worth a hard look. Sigma tells you where to look. It does not tell you to buy.
Read this first. A high positive sigma means a market is statistically unusual — nothing more. That extreme can be a genuine bargain, a data artifact (a stale home-value estimate inflating yield), or a market correctly pricing in a risk our data does not capture. Sigma is a flashlight, not a verdict. Every outlier on the leaderboard below needs human due diligence before it means anything.
| # | Market | Surface | DSCR | Gross Yield | Within-Surface σ | National Yield σ |
|---|
Ranked by national gross-yield sigma. The very top rows are exactly the cases the caveat warns about: an apparent 90%+ yield almost always means a stale or wrong home-value figure, not a real opportunity. Treat the top of this list as a data-quality queue first, an opportunity queue second.
| Surface | Primary metric | Median | Robust σ (1.4826·MAD) | Plain mean | Plain std | n |
|---|
The opportunity z-score ("sigma") for each market:
Why median + MAD, not mean + std. The whole point of this page is to find outliers. But a plain mean and standard deviation are themselves distorted by outliers: one absurd 95% yield row drags the mean up and inflates the std, which then shrinks every z-score and hides the genuine extremes. So the baseline uses robust statistics:
What's excluded. Items with no opportunity metric stay NULL — they receive no sigma and never enter the baseline. Non-finite values are dropped. The robust baseline is computed on the full non-null pool; we do not delete rows, because median/MAD already neutralise the tails.
Two sigmas per item.
opportunity_sigma is computed within each surface against
that surface's own metric (DSCR where available — milbase, collegemap, cities,
seattle — else gross yield for zipdata).
yield_sigma_national pools every market across all five surfaces
on gross yield (annual rent / home value), the one metric comparable
everywhere, and z-scores against that single national distribution. That is
what lets us say a base is "+2.7σ nationally".
Sigma bands.
typical |σ| ≤ 1 ·
notable 1–2 ·
rare 2–3 ·
exceptional > 3.
A positive sigma on DSCR or yield is a better-than-average opportunity; a
negative sigma is worse-than-average. The DSCR rate spine is the single
6.51% FRED MORTGAGE30US used across all surfaces.