Low-quality patents are of considerable concern to businesses operating in patent-dense markets. There are two pathways by which low-quality patents may be issued: the patent office may apply systematically a standard that is too lenient (low inventive step threshold); or the patent office may grant patents that are, in fact, below its own threshold (so-called 'weak' patents). This paper uses novel data from inventions that have been examined at the five largest patent offices and an explicit model of the grant process to derive first-of-their-kind office-specific estimates of the height of the inventive step threshold and the prevalence of weak patents. The empirical analysis is based on patent applications granted at one office but refused at another office. We estimate that the fraction of patent grants associated with a patent standard that is lower than that of other countries ranges from 2-15%, with Japan having the tightest standard and the United States and China the loosest. The fraction of grants that are inconsistent with the office's own standard ranges from 2-6 per cent. The fraction of grants that are inconsistent in this sense is generally higher in newer fields such as software and biotechnology, and lower in traditional fields such as mechanical engineering. Our estimates of invalidity are much lower than those that have been derived from litigation studies, consistent with litigated patents being highly non-representative of the population.
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