But, the real point here is that YOU should be trying this yourself. You just need R and package earth.
I’ll break this into three clean parts:
R,
what “earth” usually means, and
how appraisers actually use this stuff in practice.
1.
R is an open-source statistical programming language that’s very strong at:
- Multiple regression (OLS, log-linear, nonlinear)
- Hedonic price modeling
- Diagnostics (multicollinearity, heteroskedasticity, outliers)
- Graphing residuals and leverage points
- Automating repeatable analysis
In appraisal terms, R is often used for:
- Market condition (time) adjustments
- Location or amenity modeling
- Paired-sales alternatives when data is messy
- Mass appraisal / hybrid studies
- Litigation support (transparent, reproducible math)
R itself is just the engine — the real power comes from
packages (libraries).
2. What appraisers usually mean by
Short answer:
There is no mainstream appraisal or R package officially called “earth” that is known as “Package Earth” in appraisal practice.
But there
are two very common things people are usually referring to when they say this.
A)
This is probably what you’re hearing — just said imprecisely.
In
R,
earth is a real package, and it stands for:
Enhanced Adaptive Regression Splines (MARS)
What it does:
- Builds nonlinear regression models
- Automatically detects breakpoints and interactions
- Allows curves instead of straight lines
- Handles complex market behavior better than simple OLS
Why appraisers care:
- Real estate markets are not linear
- Price response to size, age, location often changes at thresholds
- MARS can model:
- diminishing returns to GLA
- age effects that flatten out
- neighborhood boundary effects
Important caution
In
lending appraisals, especially conventional SFR work:
- earth models can be hard to explain to underwriters
- USPAP requires explainability
- MARS is better suited to:
- market studies
- litigation support
- complex or atypical property analysis
- mass appraisal environments
Many residential reviewers will
reject a model they can’t easily follow, even if it’s statistically superior.
B) Confusion with
Sometimes “package earth” is sloppy shorthand for
spatial or geospatial tools, such as:
- GIS-based regression
- Latitude/longitude modeling
- Distance-to variables (coast, CBD, freeway, hazards)
- Google Earth–derived location attributes
In that case, they may mean:
- R spatial packages (e.g., for mapping or distance modeling)
- External GIS + regression workflow
- Location intelligence layered into valuation
This is
much more common in litigation or environmental proximity cases (airport noise, coastline, flood zones, Superfund sites — which you’ve dealt with).
3. How this fits into
Here’s the honest appraisal-world breakdown:
Typical residential lending appraisal
- Simple OLS regression (or paired sales)
- Possibly done in:
- Excel
- SPSS
- R (basic lm())
- Heavy emphasis on explanation, not model elegance
Advanced / litigation / consulting appraisal
- R is common
- Packages like earth may be used
- Models are:
- documented
- tested
- defensible under cross-examination
- Regression supports opinions, not replaces judgment
Mass appraisal / AVM / assessor work
- earth (MARS), random forests, boosted trees all common
- USPAP burden is different
- Explainability handled statistically rather than narratively
Bottom line
R = powerful statistical language used for regression in appraisal- earth is an R package, not a generic “earth package”
- It models nonlinear relationships, which is powerful but harder to defend in lending appraisals
There is no standalone appraisal product called “Package Earth”
