@article {Xie:2011:0003-6846:1375,
	author = "Xie, Ying and Giles, David",
	title = "A survival analysis of the approval of US patent applications",
	journal = "Applied Economics",
	volume = "43",
	number = "11",
	year = "2011",
	abstract = "We model the length of time that it takes for a patent application to be granted by the US Patent and Trademark Office (USPTO), conditional on the patent actually being awarded eventually. Survival analysis is applied and both the nonparametric Kaplan-Meier and parametric accelerated failure time models are used to analyse the data. We find that the number of claims a patent makes, the number of citations a patent makes, the patent's technological category, and the type of applicant all have significant effects on the duration that a patent is under consideration. A log-normal survival model is the preferred parametric specification, and the results suggest that the hazard function is nonmonotonic over time.",
	pages = "1375-1384",
	url = "http://www.ingentaconnect.com/content/routledg/raef/2011/00000043/00000011/art00007",
	doi = "doi:10.1080/00036840802600418"
}