
related to the compatibility of the old methodology
with the prices on the current market real estate:
Median Rate (RM) – this value is the middle rate
when arranged from low to high. Confidence
intervals are calculated around the RM. According
to the International IAAO, the RM confidence
interval should overlap with the suggested
assessment level range (0.90 – 1.10) [7]. RM is
preferred over the mean (or average) rate because it
is less likely to give misleading results if extreme
outliers (i.e., very high or very low) are in the
sample. The low level of the medians on the
studied categories indicates the underestimation of
the values obtained according to existing models.
Coefficient of Dispersion (COD) – this value
provides an estimate of how much rates spread or
disperse around the RM. Lower CODs are desirable
over higher ones as they indicate less variation and
greater precision/consistency. The IAAO
recommends COD thresholds based on property
type, jurisdiction size and market activity, which
range from 5-20% for residential properties [7], as
well as local standards [8]. COD values above
100.5% for the old models notify about the
enormous dispersion of the results as a result of the
low prediction of the old models.
Price Related Differential (PRD) – this value
provides an estimate of how much rates fluctuate
between lower, mid and higher priced properties.
PRD is centered on 1.0, with values above 1.0
suggesting regressive vertical inequity (higher
priced properties enjoy lower rates) and values
below 1.0 indicating progressive vertical inequity
(lower priced properties enjoy lower rates) [9].
The IAAO rate study standard recommends PRD
values to be between 0.98 and 1.03 [7]. When the
sample size is small or the weighted average is
heavily influenced by several extreme values of
selling prices, the PRD may become an
insufficiently reliable measure of vertical
disparities. Under the representativeness
hypothesis, high PRDs generally indicate low
valuations for high-priced properties. In case of
insufficient representativeness, extreme selling
prices may be excluded from the PRD calculation.
Similarly, for very large samples, the PRD may
become too insensitive to highlight small areas
where there is significant vertical inhomogeneity.
Price related injury (PRB) and coefficient of
variation (COV) are additional values not used in
this report. PRB is not included because
unpublished research has shown it to be a highly
flawed and misleading measure of vertical inequity
[10] COV is not included because COD is viewed
as a more appropriate measure of dispersion, which
is less likely to give misleading results if there are
extreme outliers in the sample.
3. Problem Solution
Combining the statistical and expert-analytical
methods in the development of mass real estate
valuation models is an effective approach, as both
methods have their advantages and can
complement each other. In the same vein, combined
methods rectify mutual shortcomings caused by
external and internal factors. Thus, the errors
caused by the application of the expert-analytical
method in the development of primary models are
solved by the application of complex regressions,
deduced from the statistical processing of market
data. At the same time, the errors caused by the
lack of data, the reduced level of data transparency,
as well as the invalidity of some existing statistics,
are brilliantly rectified by applying the
methodology based on empirical practice through
the expert-analytical approach. A series of measures
is proposed below by the author in order to solve
the problems addressed.
3.1. Implementation of log-linear models
Following research and examination of market
data, for residential real estate (Apartments in
multi-storey blocks, Individual houses in urban and
rural localities in the municipalities of Chisinau,
Balti, Individual garages, Orchard lots with/without
constructions and Apartments on the ground) by the
author the type of log-linear model is proposed:
; (3)
Where:
Ln(V) – The natural logarithm of the estimated
value of the real estate (lei);
Int – Intercept of the math function. It presents the
free (constant) term of the model;
i – value factor indicator;
n – the number of value factors in the model;
Ki – the constant coefficient of the value factor;
aix – value factor (independent variable) to the x
power (for nonlinear regression).
The advantages of the optimized model consist in
raising the elasticity of the nonlinear regression
between the dependent variable (V) and the value
factors. Log-transforming the variables in a
regression model is a very common way to handle
situations where there is a nonlinear relationship
between the independent and dependent variables.
Using the logarithm of one or more variables
Financial Engineering
DOI: 10.37394/232032.2024.2.12