The reliability of the results derived from the comparable uncontrolled price method is affected by the completeness and accuracy of the data used and the reliability of the assumptions made to apply the method. See § 1.482-1(c) (Best method rule) ...

Deficiencies in the data used or assumptions made may have a greater effect on some methods than others. In particular, the reliability of some methods is heavily dependent on the similarity of property or services involved in the controlled and uncontrolled transaction. For certain other methods, such as the resale price method, the analysis of the extent to which controlled and uncontrolled taxpayers undertake the same or similar functions, employ similar resources, and bear similar risks is particularly important. Finally, under other methods, such as the profit split method, defining the relevant business activity and appropriate allocation of costs, income, and assets may be of particular importance. Therefore, a difference between the controlled and uncontrolled transactions for which an accurate adjustment cannot be made may have a greater effect on the reliability of the results derived under one method than the results derived under another method. For example, differences in management efficiency may have a greater effect on a comparable profits method analysis than on a comparable uncontrolled price method analysis, while differences in product characteristics will ordinarily have a greater effect on a comparable uncontrolled price method analysis than on a comparable profits method analysis ...

All methods rely on certain assumptions. The reliability of the results derived from a method depends on the soundness of such assumptions. Some assumptions are relatively reliable. For example, adjustments for differences in payment terms between controlled and uncontrolled transactions may be based on the assumption that at arm’s length such differences would lead to price differences that reflect the time value of money. Although selection of the appropriate interest rate to use in making such adjustments involves some judgement, the economic analysis on which the assumption is based is relatively sound. Other assumptions may be less reliable. For example, the residual profit split method may be based on the assumption that capitalized intangible development expenses reflect the relative value of the intangible property contributed by each party. Because the costs of developing an intangible may not be related to its market value, the soundness of this assumption will affect the reliability of the results derived from this method ...

The completeness and accuracy of the data affects the ability to identify and quantify those factors that would affect the result under any particular method. For example, the completeness and accuracy of data will determine the extent to which it is possible to identify differences between the controlled and uncontrolled transactions, and the reliability of adjustments that are made to account for such differences. An analysis will be relatively more reliable as the completeness and accuracy of the data increases ...

Whether a method provides the most reliable measure of an arm’s length result also depends upon the completeness and accuracy of the underlying data, the reliability of the assumptions, and the sensitivity of the results to possible deficiencies in the data and assumptions. Such factors are particularly relevant in evaluating the degree of comparability between the controlled and uncontrolled transactions. These factors are discussed in paragraphs (c)(2)(ii) (A), (B), and (C) of this section ...

The requirement to use the most reliable information will usually, but not always, require the use of local comparables over the use of regional comparables where such local comparables are reasonably available. The use of regional comparables in transfer pricing documentation prepared for jurisdictions in the same geographic region in situations where appropriate local comparables are available will not, in some cases, comport with the obligation to rely on the most reliable information. While the simplification benefits of limiting the number of comparable searches an entity is required to undertake are obvious, and materiality and compliance costs are relevant factors to consider, a desire for simplifying compliance processes should not go so far as to undermine compliance with the requirement to use the most reliable available information. See paragraphs 1.132-1.133 on market differences and multi-jurisdictional analyses for further details on when local comparables are to be preferred ...