I took an interest in Helendale, CA, because it is a PITA, i.e., hard to appraise area, and situated in the Mojave Desert. The analysis below is a trilogy: MARS (multivariate adaptive regression spline) + GLR (generalized linear regression) + GAM (generalized additive models). For MARS, CRAN earth() is used, for GLR, CRAN glmnet is used, and for GAM, CRAN mgcv is used. These are all 3 very popular statistical regression packages.
For appraisal, MARS is considered number 1 for regression because it provides the appraiser with an interpretable model. GLR is excellent for providing a robust target estimate and is fast, and GAM is good at providing smooth value functions - when it works.
Helendale has been called a PITA to appraise (above), and it is. It has a lot of noise, and many comments could be made about it. It is surprising that earthUI (MARS) and glmnetUI (GLR) performed so well on it; the values they produced were very close. mgcvUI had problems due to noise and other issues in the data. Usually (e.g., Burlingame, CA) mgcvUI also comes up with a target value that is close to the others.
By the way, the value discussed is from a recent sale I randomly chose, and I just gave it an average CQA of 5.00 for the sake of discussion. I have never been to Helendale myself, and of course, what I am presented is strictly just a run of the data through the stat routines. I did categorize water view, which, for Helendale, appears to be an important value contribution. But I have done this without spending any time in Helendale, so I could be off on a few points.
In the link below, there is a comparative analysis followed by the 3 different reports.
I couldn't include the MLS data since it is proprietary, and I didn't want to create altered data. So, no data is included, just the models and graphs and some discussion.
To reiterate, what is stated in the report is not an appraisal.