Patent searches for clearance investigations differ from prior art searches to determine potential patentability, in several ways.

1. Clearance searches typically focus only on patents that issued recently enough to be potentially unexpired, whereas patentability searches should reach back to all prior art that precedes the subject invention.
2. Patents identified in a clearance search are reviewed for the scope of their claim coverage, whereas prior art documents identified in a patentability search are considered for everything that they disclose, whether claimed or not. The claim scope review of patents identified in a clearance search considers strengths and defects in the claim coverage, which generally requires analysis of the prosecution history of the patent’s allowance. By contrast, pre-filing patentability searches generally do not require review and analysis of the prosecution history of prior art patents listed in the search results.
3. A client’s own patents can be ignored in a clearance search, because the client will not assert its own patents against itself. By contrast, a client’s own prior disclosures in past publications or patent documents may be relevant to patentability, and so must be considered in a patentability search.
4. Published prior patent applications are as important in a patentability search as are issued patents. However, in a clearance search, published patent applications are usually less important because they do not yet confer enforceable rights, and the published claims may differ from the claims that may be subsequently allowed (if any).

Although the primary audience for reviewing the results of a patent search is usually a client’s patent attorney, it is often possible to reduce costs by contracting with a lower-cost or specialized vendor to perform the initial search and results screening. Sometimes employees of the client can perform the search, further reducing search costs to the client. Ultimately, however, the patent attorney will have to assess the relevance of the search results potential infringement or patentable claim scope.

The cost of each patent search also depends upon the scope of the search and the client’s tolerance of risk. After all, the patent databases are large and additional searches of various scope and with different keywords are always possible. Searches of different scope and using different keywords naturally lead to different lists of search results, and no single search can guarantee that all relevant patents have been identified. Indeed, the relevance of most design patents and some utility patents can be determined only by human review of the drawings, in which case several keyword searches still may be unlikely to discover the relevance.

Therefore, more searching and review can always further reduce the ever-present risk that an important patent might be missed, yet more searching and review increases the cost of the search. Hence, there is always a balance between the cost of the search and review, versus the risk that an important patent might be missed.

Different legal situations may drive a client’s risk tolerance. For example, the potential adverse legal consequences of an insufficiently comprehensive clearance search prior to product launch, or in the context of a pre-filing search to inform the drafting of an inter partes review (IPR) petition, may be far greater than the legal consequence for an insufficiently-comprehensive search done to inform the drafting of a patent application (where subsequent claim amendments are not desirable but possible).

Hence, the scope and depth of patent searching and review that may be cost-justified to a client may depend not only on the client’s resources but also on the legal situation in which the need for patent searching arises.