In the US patent applicants and patent attorneys operate under a duty to disclose to the USPTO "all information known to that individual to be material to patentability." 37 C.F.R. 1.56. Here, material to patentability is defined as non-cumulative information that either (1) "establishes, by itself or in combination with other information, a prima facie case of unpatentability of a claim" or (2) is inconsistent with a position taken by the applicant before the USPTO. Id. Typically, the duty of disclosure is fulfilled through the process of submitting information disclosure statements (IDSs) to the USPTO along with copies of the actual material information (such as prior art references).
Over the past 13 years, the number of references cited per patent has grown dramatically as shown in the chart below that shows the average number of references cited both by Applicants and Examiners as seen on the face of issued patents.