The threshold necessary for initiating an Inter Partes Review (IPR) is prescribed by statute as a reasonable likelihood that a petitioner will prevail (RLP) with respect to at least one challenged claim. On the other hand, the threshold necessary to trigger a Post Grant Review (PGR) is prescribed by statute as more likely than not that a challenged claim is unpatentable. Absent review of the legislative history, it is far from straightforward as to the difference in these standards. Fortunately, the PTO has issued an explanation clarifying the difference.On the AIA micro-site, Chief Judge Smith explained the difference as follows:
Comparing the two standards, the “reasonable likelihood” standard is lower than the “more likely than not” standard. The reasonable likelihood standard allows for the exercise of discretion but encompasses a 50/50 chance whereas the “more likely than not” standard requires greater than a 50% chance of prevailing.
Petitioners are encouraged to clearly set forth the best ground of unpatentability as to each challenged claims to facilitate early resolution of the issues. In instituting an IPR or PGR, the Board may take into account whether the same or substantially same prior art or arguments previously were presented to the Office. 35 U.S.C. 315(d) and 325(d). Additionally, the Board may also go forward on challenged claims that are unpatentable based on obviousness where challenge is based on anticipation.
I am not sure there is a significant enough difference between the two standards to make much of an impact between grant rates. Yet, with the broader estoppel effect and more liberal discovery practice in PGR, the higher threshold standard provides yet another reason to avoid this proceeding in favor of IPR, given the option.