concurring in the result:
Today the court exercises appropriate discretion in declining to decide whether section 355(l) and FOIA Exemption 4 are congruent, because it is unnecessary to do so to resolve the dispute before us. I believe the court errs, however, in not exercising similar restraint with respect to an issue regarding the meaning of Exemption 4 itself.
My colleagues hold that in determining whether a document comes within Exemption 4, the court may not “gauge whether the competitive harm” disclosure would cause to the company that submitted the document “is outweighed by the public interest in safeguarding” human health. Maj. Op. at 903. This means that even if disclosure were the only way to prevent the loss of human life, that would count for nothing as against a showing by the company that disclosure would cause substantial harm to its competitive position. See id. at 905 (“[W]e do not consider Public Citizen’s assertion that disclosure would in fact prevent the exposure of human beings to a health risk.”). This is an important issue, and the kind that should be decided only after full briefing and argument. See, *908e.g., Carducci v. Regan, 714 F.2d 171, 177 (D.C.Cir.1983).
But we have not had that here. As the argument heading of Public Citizen’s brief makes clear, its core Exemption 4 argument was that the requested records “Do Not Constitute Confidential Commercial Information.” Public Citizen Br. at 31. In a single clause in a single sentence of that brief, Public Citizen also said: “Any disadvantage to Schering is minimal, and is outweighed by the strong public interest in safeguarding the health of human trial participants.” Id. at 34 (emphasis added). Schering replied in kind. In a single clause in a single sentence of its reply brief (and without citation), Schering said: “This enterprise [pharmaceutical research] has well-served the public health through the discovery and development of new medicines and should not, in effect, be reorganized to suit Public Citizen’s views through an unprecedented and strained reading of exemption A” Schering Reply Br. at 6 (emphasis added). The italicized phrases are the full extent of the argument we have heard on this issue. The FDA did not mention the point at all; the parties did not discuss it at oral argument; and the district judge did not refer to it in his opinion.
Nor is this an issue we must decide in order to dispose of this case. Even if a balancing of the public safety interest in disclosure were an element of Exemption 4, and even if Public Citizen had intended to raise the point, the conclusory assertion the court cites is insufficient to prevent the entry of summary judgment in favor of the FDA. As we have said many times before, “[i]t is well settled that [cjonclusory allegations unsupported by factual data will not create a triable issue of fact.” Exxon Corp. v. FTC, 663 F.2d 120, 126-27 (D.C.Cir.1980) (internal quotation omitted); see Alyeska Pipeline Serv. Co. v. EPA 856 F.2d 309, 313-14 (D.C.Cir.1988); Gardels v. CIA, 689 F.2d 1100, 1106 (D.C.Cir.1982); Military Audit Project v. Casey, 656 F.2d 724, 749 (D.C.Cir.1981).1
Nor is this a case where the legal conclusion the court has reached is indisputable. To the contrary, although no party cited the relevant precedent on this point, we have twice held that Exemption 4 requires a balancing of the interest in nondisclosure “against the public interest in disclosure.” See Washington Post Co. v. HHS, 690 F.2d 252, 269 (D.C.Cir.1982) (Washington Post I); Washington Post Co. v. HHS, 865 F.2d 320, 326-27 (D.C.Cir.1989) (Washington Post II). Washington Post I involved an analysis of Exemption 4 under the “impairment” prong of the National Parks test for confidential information.2 We held that “[t]his inquiry necessarily involves a rough balancing of the extent of impairment and the importance *909of the information against the public interest in disclosure.” Washington Post I, 690 F.2d at 269. Rather than decide “the details of the balancing process,” we remanded the case to the district court. Id. When the case later returned to us, we concluded that the interest the government asserted in nondisclosure — impairment of its information-gathering ability— had not been appropriately resolved. We therefore remanded the case again, instructing that “if the district court ultimately finds that disclosure will impair the government’s information-gathering, it will once again be required to conduct the ‘rough balancing of the extent of impairment and the importance of the information against the public interest in disclosure.’ ” Washington Post II, 865 F.2d at 326-27 (quoting Washington Post I, 690 F.2d at 269). And we made clear that “the only inquiry properly before the district court was the question whether disclosure of the financial information ... would be likely to impair the government’s ability to gather this information in the future, and if so whether this risk outweighed the public’s interest in disclosure.” Id. at 324-25 (emphasis added).3
None of the cases cited by the court holds that the public safety interest in disclosure should not be weighed in applying FOIA Exemption 4. Certainly Reporters Committee does not. See United States Dep’t of Justice v. Reporters Comm. for Freedom of the Press, 489 U.S. 749, 773, 109 S.Ct. 1468, 103 L.Ed.2d 774 (1989). In that case there was no question but that a balancing test was required with respect to Exemption 7(C), id. at 776, 109 S.Ct. 1468; the question was what interests could be weighed in the balance. The Supreme Court held that FOIA does not protect an interest in “disclosure of information about private citizens that is accumulated in various governmental files but that reveals little or nothing about an agency’s own conduct.” Id. at 773, 109 S.Ct. 1468. But as my colleagues recognize, the Court also held that an interest in “[o]fficial information that sheds light on an agency’s performance of its statutory duties falls squarely within that statutory purpose” and may be weighed in the balance. Id.
Unlike the information sought in Reporters Committee, the information Public Citizen seeks may reveal much about “an agency’s performance of its statutory duties.” All of the records sought pertain to clinical trials that could not have proceeded without FDA authorization, and that “were discontinued ... because of death or serious injury of patients.” FDA Br. at 2 (describing Public Citizen’s FOIA request). Disclosure assertedly will reveal “whether the FDA is adequately analyzing data submitted in INDs before allowing human testing to begin and whether safety problems uncovered in clinical trials result in prompt cessation of those trials.” Public Citizen Br. at 5. That would certainly permit the public to “learn something directly about the workings of the Government.” Maj. Op. at 904 (quoting National Ass’n of Retired Fed. Employees v. Horner, 879 F.2d 873, 879 (D.C.Cir.1989)). *910Yet, in evaluating the government’s Exemption 4 claims, the court makes no effort to determine how important to the public interest learning such information would be,4 or to weigh it against the injury Schering would suffer from disclosure. Instead, the court ends its analysis upon finding “that disclosure of information in this IND would cause [Schering] substantial competitive harm.” Id. at 12.
I cannot dispute my colleagues’ conclusion that the briefs’ brief mention of this issue gives us the discretion to decide it. But that is “not to say that affirmative exercise of the discretion [is] wise.” Fraternal Order of Police v. United States, 173 F.3d 898, 903 (D.C.Cir.1999), reconsidering Fraternal Order of Police v. United States, 152 F.3d 998 (D.C.Cir.1998). Deciding an issue in the absence of any substantive briefing may later make us wish that we had waited. See id. (“In retrospect, it may well have been imprudent to address the merits on so thin an argumentative record.”). For that reason, I would “decline to resolve this issue on the basis of briefing which consisted of [not even] three sentences in the ... brief and no discussion of the ... relevant case law.” Railway Labor Executives’ Ass’n v. United States R.R. Retirement Bd., 749 F.2d 856, 859 n. 6 (D.C.Cir.1984) (citing Carducci, 714 F.2d at 177); see Washington Legal Clinic for the Homeless v. Barry, 107 F.3d 32, 39 (D.C.Cir.1997).
. The court notes that in addition to the single conclusory statement in its brief, Public Citizen also mentioned the point in an affidavit filed in district court. Op. at 903 n.*. But as my colleagues' recitation of statements from the affidavit makes clear, that mention is confined to a total of three sentences in that 12-page document. See JA 312 (opining that "the public will benefit significantly from their release” and that "if these studies are kept secret, other drug companies may unknowingly conduct similarly hazardous studies, potentially placing many patients needlessly at risk”) (emphasis added); id. at 309 (alleging that disclosure "decreases the likelihood that other drug companies will replicate potentially hazardous human testing”). As the cases cited in the text above indicate, these conclusory statements of affiant opinion are insufficient to defeat a motion for summary judgment. See also 10B Charles Alan Wright, Arthur R. Miller & Mary Kay Kane, Federal Practice & Procedure § 2738, at 346-56 (3d ed. 1998).
. Under the test employed in National Parks & Conservation Ass'n v. Morton, 498 F.2d 765, 770 (D.C.Cir.1974), "commercial or financial matter is ‘confidential’ for purposes of the exemption if disclosure of the information is likely to have either of the following effects: (1) to impair the Government's ability to obtain necessary information in the future; or (2) to cause substantial harm to the competitive position of the person from whom the information was obtained.” Nothing in the reasoning of Washington Post I suggests that the public interest balancing it requires for prong (1) is not also required for prong (2).
. See also Martin v. Lauer, 686 F.2d 24, 33 (D.C.Cir.1982) ("A decision whether to release FOIA-exempt material ... requires a considered balancing of the public’s interest in disclosure of particular material and the interests in nondisclosure acknowledged by the statutory exemptions.”). The Ninth Circuit has followed our approach, see GC Micro Corp. v. Defense Logistics Agency, 33 F.3d 1109, 1115 (9th Cir.1994) ("We agree with the D.C. Circuit that, in making our determination [of competitive harm under Exemption 4], we must balance the strong public interest in favor of disclosure against the right of private businesses to protect sensitive information.”), as has our own district court, see Public Citizen Health Research Group v. FDA, 964 F.Supp. 413, 415 (D.D.C.1997) (citing Teich v. FDA, 751 F.Supp. 243, 253 (D.D.C.1990); AT&T Info. Sys., Inc. v. General Servs. Admin., 627 F.Supp. 1396, 1403 (D.D.C.1986)). See also 1 James T. O’Reilly, Federal Information Disclosure § 14.12, at 14-44 (2d ed.1990) ("In some cases the public need for the information is factored by the court into its equation of substantial competitive harm.... For example, public health and safety factors may warrant more attention to the substantial harm equation....”).
. One, but only one, of the elements of the public interest asserted by Public Citizen is that disclosure would "save human trial participants from being exposed to a dangerous drug" by keeping other drug companies from replicating Schering's "hazardous human testing.” Op. at 905, 903 n.* (quoting Public Citizen). As noted above, on the current record this is only a conclusory allegation. But if in fact the FDA has not already protected human trial participants directly by barring authorization for such replicated studies, disclosure of Schering’s studies will reveal that fact (to the drug companies, trial participants, their physicians, and other knowledgeable members of the public). By thus revealing the FDA’s failure to "perform! ] its statutory duties,” Reporters Committee, 489 U.S. at 773, 109 S.Ct. 1468, disclosure may enable the public to protect itself.