Abstract
Often completeness of search results is an important demand. If not, the degree of recall should at least be estimated. A simple direct search example combining a chemical with an electrical aspect is executed on several patent databases, WPI, USP, CLAIMS, CA and JAPIO, using the special features of each of them. As one result consideration of paraphrases and special aspects is necessary even for straight-forward search terms with clear definitions like electrode. The other and main result is an unexpectedly high necessity for the use of additional databases: even the best database retrieves only 50–65% of the total result, and even the fourth database adds a considerable amount of relevant information to the results of three other databases.
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