There are three general groups of methodologies for determining value. These are usually referred to as the "three approaches to value":
The appraiser will determine which one or more of these approaches may be applicable, based on the scope of work determination, and from that develop an appraisal analysis. Costs, income, and sales vary widely from one situation to the next, and particular importance is given to the specific characteristics of the subject.
Consideration is also given to the market for the property appraised. Appraisals of properties that are typically purchased by investors (e.g. - skyscrapers) may give greater weight to the income approach, while small retail or office properties, often purchased by owner-users, may give greater weighting to the sales comparison approach. While this may seem simple, it is not always obvious. For example, apartment complexes of a given quality tend to sell at a price per apartment, and as such the sales comparison approach may be more applicable. Single family residences are most commonly valued with greatest weighting to the sales comparison approach, but if a single family dwelling is in a neighborhood where all or most of the dwellings are rental units, then some variant of the income approach may be more useful.
The cost approach
The cost approach was formerly called the summation approach. The theory is that the value of a property can be estimated by summing the land value and the depreciated value of any improvements. The value of the improvements is often referred to by the abbreviation RCNLD (reproduction cost new less depreciation or replacement cost new less deprecation). Reproduction refers to reproducing an exact replica. Replacement cost refers to the cost of building a house or other improvement which has the same utility, but using modern design, workmanship and materials. In practice, appraisers use replacement cost and then deduct a factor for any functional disutility associated with the age of the subject property.
In most instances when the cost approach is involved, the overall methodology is a hybrid of the cost and sales comparison approaches. For example, while the replacement cost to construct a building can be determined by adding the labor, material, and other costs, land values and depreciation must be derived from an analysis of comparable data.
The cost approach is considered reliable when used on newer structures, but the method tends to become less reliable for older properties. The cost approach is often the only reliable approach when dealing with special use properties (e.g. -- public assembly, marinas).
The sales comparison approach
The sales comparison approach examines the price or price per unit area of similar properties being sold in the marketplace. Simply put, the sales of properties similar to the subject are analyzed and the sale prices adjusted to account for differences in the comparables to the subject to determine the value of the subject. This approach is generally considered the most reliable if adequate comparable sales exist. In any event, it is the only independent check on the reasonability of an appraisal opinion.
Note that this approach develops value from a purely pricing scheme, and as such is an example of a revealed preference model. An interesting perspective on the relationship between relatively subjective human estimation as compared with that obtained by purely mathematic modeling is contained in "Simple Heuristics That Make Us Smart" by Gerd Gigerenzer. Dr. Gigerenzer, a psychologist, asked people to estimate some real world facts based simply on their knowledge, experience and impressions. Common knowledge and some simple rules created models which were close to those produced by multiple regression analysis (MRA) and neural networks. The predictive value of the human models applied to a new sample was a bit better than the mathematical models, suggesting that the mathematical models may have described the data better but missed the predictive relationships. Similarly automated valuation models frequently find building size (square feet or meters) predictive of value, even when that information is not explicitly advertised. This is similar to the example in "The Wisdom of Crowds", Surowiecki, in which the scientist Francis Galton observed a crowd at a fair to, on average, accurately estimate the size
The income capitalization approach
The income capitalization approach is used to value commercial and investment properties.
In a commercial income producing property this approach capitalizes an income stream into a present value. This can be done using revenue multipliers or single-year capitalization rates of the Net Operating Income. The Net Operating Income (NOI) is gross potential income (GPI), less vacancy (= Effective Gross Income) less operating expenses (but excluding debt service or depreciation charges applied by accountants).
Alternatively, multiple years of net operating income can be valued by a discounted cash flow analysis (DCF) model. The DCF model is widely used to value larger and more expensive income-producing properties, such as large office towers.
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