concurring.
Although I concur in the result that the Court reaches, I respectfully disagree with the reasons it relies upon to reach this result. Although I agree that the motion justice properly granted Garden City Treatment Center, Inc.’s (Garden City) summary-judgment motion, I respectfully disagree with the rationale that the provider contracts in question forbade the use of statistical sampling as an auditing methodology. Rather, I would hold that the contractual language in question did not prevent Blue Cross and Blue Shield of Rhode Island and Coordinated Health Partners, *545Inc. (collectively, defendants) from using statistical-sampling methods to prove the alleged overcharges. Nevertheless, because the defendants failed to satisfy their burden of showing the propriety of the statistical-sampling methods they relied upon to justify their conclusion that a certain portion of Garden City’s claims for payment were invalid — and, consequently, that defendants were entitled to recoup any overpayments from Garden City — I agree that the entry of a summary judgment in favor of Garden City was appropriate.
The defendants’ use of statistical sampling was a means of proving the alleged impropriety of Garden City’s claims for payment and defendants’ conclusion that Garden City overcharged them. The provider agreements did not preclude them from doing so. Indeed, the contracts were silent about what methods defendants could employ to show any alleged overcharges or invalid claims. As shown below, statistical sampling is a widely accepted technique to audit, monitor, or review voluminous quantities of claims data, especially when a claim-by-claim examination would be impractical or unnecessary to guarantee the accuracy of any conclusions reached about whether defendants overpaid Garden City with respect to any of the claims at issue.
Nevertheless, I would hold that the motion justice properly granted summary judgment in favor of Garden City because defendants failed to prove the legitimacy of their statistical-sampling methods in their opposition to Garden City’s summary-judgment motion. A party opposing a summary-judgment motion has an affirmative duty to set forth specific facts, by affidavit or otherwise, showing the existence of a genuine issue of material fact. Mills v. Toselli, 819 A.2d 202, 205 (R.I. 2003) (per curiam). Parties opposing a
summary-judgment motion cannot merely rest upon their pleadings to establish the existence of a disputed factual issue that would require a trial. Clift v. Narragansett Television, L.P., 688 A.2d 805, 813 (R.I.1996). And they cannot defend against a summary-judgment motion merely by suggesting that they can or will prove their conclusions and allegations later at a trial. Granoff Realty II, L.P. v. Rossi 833 A.2d 354, 362 (R.I.2003) (per curiam). Here, I am of the opinion that the grant of summary judgment was appropriate solely because defendants did not satisfy their burden of showing the existence of a genuine issue of material fact with respect to the validity of their conclusions about the alleged overcharges and improper claims based on their statistical sampling of a subset of Garden City’s claims for payment. Instead, defendants merely established what I consider to be an irrelevant point: that the provider agreements were ambiguous about whether the parties contemplated that defendants could use statistical sampling to prove that Garden City’s claims were invalid. Although defendants indicated that, if given the opportunity, they would produce competent evidence showing that the parties anticipated defendants’ use of statistical sampling when they entered into the provider agreements, this, to me, was a red herring and, in any event, it was not enough to avoid summary judgment.
I conclude that the contractual-authorization issue was irrelevant because, whether the contracts authorized statistical sampling or not, defendants were entitled, as an evidentiary matter, to use statistical sampling to prove their contention that a substantial portion of Garden City’s claims were invalid and that the claims in question otherwise overstated its entitlement to receive payments from defendants under the applicable provider agreements.
*546Unfortunately, however, defendants erred in making contractual ambiguity the keystone of their opposition to summary judgment because the issue of whether the contracts were ambiguous in this respect was a question of law for the court to decide. See, e.g., Rotelli v. Catanzaro, 686 A.2d 91, 94 (R.I.1996); Westinghouse Broadcasting Co. v. Dial Media, Inc., 122 R.I. 571, 579, 410 A.2d 986, 991 (1980). Therefore, once the motion justice erroneously deemed the contracts to be unambiguous, defendants failed to show a genuine issue of material fact about whether Garden City had submitted improper claims that justified defendants’ actions. And defendants also pressed an equally unavailing argument when they asserted that they would be able to produce extrinsic evidence at a later date showing that the parties contemplated statistical sampling when they entered into the agreements.
As discussed above, a party cannot defeat a summary-judgment motion by merely resting on the pleadings or by indicating that they will be able to prove their claims or defenses at some future date or at trial. Instead, defendants should have opposed Garden City’s summary-judgment motion by submitting expert affidavits demonstrating the reliability of their statistical sampling and auditing conclusions with respect to the claims in question.
In fact, such auditing methods are common, and courts generally admit statistical sampling evidence to prove a given party’s claims or defenses — provided expert testimony validates the methods used to reach the conclusions in question. See generally, Gregory Todd Jones & Reidar Hagtvedt, Sample Data as Evidence: Meeting the Requirements ofDaubert and the Recently Amended Federal Rules of Evidence, 18 Ga. St. U.L. Rev. 721, 721 (2002) (hereinafter Jones & Hagtvedt). Hence, rather than limiting its summary-judgment opposition to contract-interpretation issues, defendants should have argued that the rules of evidence allowed them to introduce, through expert testimony, the data and conclusions they derived from the statistical-sampling techniques they used — even if the contracts had been silent on this subject and even if the contracts had failed to expressly authorize the use of such techniques.
Statistical sampling, or sample adjudication, “involves collecting samples from a given population — a small subset of the relevant persons or things — deriving statistics from this sample data, and arriving at conclusions regarding the population based upon these sample statistics.” Id. Courts are increasingly “willing to admit evidence based upon sample data.” Id. at 722. Thus, courts have allowed statistical-sampling evidence in motions for change of venue, trademark and advertising litigation, pornography and drug-trafficking prosecutions, copyright infringement and software-piracy cases, auditing of waste, fraud, and abuse of welfare programs, labor and employment litigation, and other contexts. See id. at 728-24 (collecting cases). All these courts admitted statistical-sampling results into evidence because the examination of vast quantities of data on a case-by-case basis or claim-by-claim review would be too costly and impractical to undertake. “The logic of sample adjudication, accepted by courts that have approved the technique in other contexts, is that any minor errors will tend to balance out in the end.” Chaves County Home Health Service, Inc. v. Sullivan, 931 F.2d 914, 919 (D.C.Cir.1991).
Thus, “[m]ost often, courts allow statistical[-]sampling evidence as the basis for expert opinion testimony.” Jones & Ha-gtvedt, 18 Ga. St. U.L. Rev. at 727. If defendants had included expert affidavits and evidentiary arguments in their opposi*547tion to Garden City’s summary-judgment motion, the motion justice should have denied the summary-judgment motion and then proceeded to determine whether defendants’ statistical-sampling evidence was potentially admissible as expert testimony under Rules 7027 and 7038 of the Rhode Island Rules of Evidence. Such evidence is generally admissible if it is relevant and if it will assist the trier of fact. See State v. Wheeler, 496 A.2d 1382, 1388 (R.I.1985). In determining whether defendants’ proffered statistical-sampling evidence would assist the trier of fact in determining the amount of any alleged invalid claims or overpayments, the motion justice could have considered, for example, whether the samples that defendants examined were random and whether the samples were significant and representative enough to justify applying the rate of overpayment derived from the samples to the entire universe of Garden City’s challenged claims. See Jones & Hagtvedt, 18 Ga. St. U.L. Rev. at 739-46 (listing factors federal courts should consider pertaining to statistical samples under the Federal Rules of Evidence).
The defendants’ ability to prove their overcharge case in court did not depend on the presence or absence of a contractual provision authorizing them to use certain evidentiary techniques to establish the invalidity of Garden City’s challenged claims. The rules of evidence and civil procedure — not the presence of unambiguous contract provisions — provide parties with the means of proving their claims and defenses. Jones & Hagtvedt, 18 Ga. St. U.L. Rev. at 727 (courts allow statistical sampling evidence as the basis for expert opinion testimony subject to Rule 703 of the Federal Rules of Evidence). Thus, absent some valid contractual provision or law preventing them from doing so, and subject to the rules of evidence governing the admission of expert testimony, I would hold that parties may freely use statistical sampling as a method of proving alleged overcharges in situations such as the one presented by the case at bar. See id.
I would also hold that the ability of defendants to use statistical sampling to prove that Garden City breached its contractual obligations by submitting invalid claims and by receiving payments for unauthorized health-care procedures did not depend on any contractual provision specifically authorizing this method of proof. Indeed, even if the relevant contracts were silent on this issue and even if (contrary to the facts in this case) they said nothing about defendants’ ability to audit, verify, or monitor Garden City’s claims, Garden City still was not entitled to overcharge defendants or to submit invalid claims for payment. Consequently, defendants were entitled to prove that Garden City, in fact, had submitted invalid claims or otherwise overcharged them by whatever legitimate evidentiary measures they could muster, including statistical sampling based upon analyzing and extrapolating from reliable *548samples of the putative invalid claims. See, e.g., Illinois Physicians Union v. Miller, 675 F.2d 151, 156 (7th Cir.1982) (determining that use of statistical sampling was proper as long as the opposing party had an opportunity to rebut the initial determination of an overpayment).
In any event, far from constituting a nefarious practice or one that depends on specific contractual authorization for its validity, statistical sampling is a well-established auditing technique in situations, as here, in which a claim-by-claim review of voluminous documents may not be feasible. Thus, numerous courts have upheld its use in the context of state and federal government agencies seeking to recoup alleged Medicare and Medicaid overpayments. See Ratanasen v. California, Department of Health Services, 11 F.3d 1467, 1471 (9th Cir.1993) (Medicaid); Yorktown Medical Laboratory, Inc. v. Perales, 948 F.2d 84, 89-90 (2d Cir.1991) (Medicaid); Chaves County Home Health Service, Inc., 931 F.2d at 919 (Medicare); Illinois Physicians Union, 675 F.2d at 155 (Medicaid); In re Mercy Hospital of Watertown v. New York State Department of Social Services, 79 N.Y.2d 197, 581 N.Y.S.2d 628, 590 N.E.2d 213, 219 (1992) (Medicaid). “[CJourts have routinely permitted the use of statistical sampling to determine whether there has been a pattern of overpay-ments spanning a large number of claims where case-by-case review would be too costly.” Chaves County Home Health Service, Inc., 931 F.2d at 919. See also Kirby D. Behre & A. Jeff Ifrah, Statisticians at DOJ May Overstate Case: Government’s Use of Statistical Sampling to Prove False Claims Act Liability, Damages May Be Unreliable, If Not Impermissible, 21 Nat’l L.J. B6 (Mar. 29, 1999) (“[C]ase law arising from Health and Human Services (HHS) recoupment actions has consistently upheld the government’s use of random sampling * * *.”).
Contrary to Garden City’s assertions, these Medicare and Medicaid decisions do not rest on explicit statutory or contractual authority granting these agencies the right to use reasonable means, such as statistical sampling, to calculate and to recover alleged overpayments. For example, in Chaves County Home Health Service, Inc., 931 F.2d at 917, the court noted that the Department of Health and Human Services did “not contend that its sample adjudication scheme for post-payment review of coverage determinations [was] based on explicit statutory authorization; it relie[d] instead on its general (and uncontested) authority to recoup overpayments from [its] providers.” Thereafter, the court reemphasized thát a Department of Health and Human Services ruling (HFCA Ruling 86-1) “was not the source of administrative authority in these cases but merely explained and reaffirmed the Department’s long-standing and well-established practice of conducting sample audits.” Chaves County Home Health Service, Inc., 931 F.2d at 923 (emphases added); see also Mercy Hospital of Watertown, 581 N.Y.S.2d 628, 590 N.E.2d at 216, 217 (upholding statistical sampling in Medicaid re-coupment action even though “the legislation delegating to DSS the authority to administer the Medicaid program does not expressly or impliedly authorize the use of random sample audits”).
Here, as in the Medicare and Medicaid cases, I would hold that defendants did not need any contractual or statutory authorization to use statistical sampling as a means to prove and recover overpayments for uncovered or otherwise invalid claims that were contrary to what the contracts required to trigger claims payments by defendants. In any event, the provider agreements broadly stated that defendants “shall have the right, upon request, to verify all * * * medical records * * * for *549the purpose of monitoring billing.” As in the above-cited cases upholding statistical sampling as a method of proving overcharges, I conclude that defendants properly used statistical sampling as a billing verification or monitoring technique — pursuant to this above-quoted contractual authority for them to do so. The contract did not purport to limit the means or methods that defendants might use to accomplish the billing verification and monitoring that the contract expressly permitted. Thus, I would hold that even if they needed contractual authorization to engage in statistical sampling, defendants’ general contractual right to “monitor[ ] billing,” “to verify all * * * medical records,” and to recoup overpayments granted them the right to use statistical sampling as a means to monitor Garden City’s billing, verify its claims, and recoup any resulting overpay-ments.
In addition, notwithstanding Garden City’s arguments to the contrary, the above-cited Medicare and Medicaid decisions did not turn on the fact that the party seeking recoupment was a federal or state government agency, as opposed to a private health-care insurer. The courts issuing these decisions did not cite any legal or public-policy reasons that would limit their holdings to government agencies seeking to recover publicly-funded reimbursements. Indeed, as mentioned previously, courts have accepted statistical sampling evidence in a variety of civil-litigation contexts — such as trademark and advertising cases — in which neither party was a government agency. See Jones & Ha-gtvedt, 18 Ga. St. U.L. Rev. at 728-25.
Conclusion
This is a case about alleged overpay-ments by health-care insurers to a healthcare provider based on the provider’s alleged submission to the insurers of supposedly invalid claims for payment. The defendant health-care insurers were entitled to prove such alleged invalid claims and overpayments by whatever legitimate means they could use to do so — including statistical sampling — regardless of whether the contracts in question specifically allowed them to prove such overcharges by this method. Although the contracts expressly allowed defendants to verify medical records and to monitor Garden City’s billing, defendants failed to show, opposing Garden City’s summary-judgment motion, that the statistical sampling methods they used to monitor and verify Garden City’s billing were legitimate and valid.
Based on the foregoing analysis, the motion justice’s grant of summary judgment would have been inappropriate if the defendants had opposed the motion by submitting one or more expert affidavits establishing the validity of them statistical-sampling methods. Instead, the defendants limited them opposition to proving an irrelevant point: that the provider agreements were ambiguous about permitting the use of statistical-sampling methods to audit Garden City’s payment claims. But regardless whether the contracts were ambiguous, silent, or expressly permitted the defendants to use statistical sampling, I am of the opinion that, absent any contractual provision or law barring them from doing so, the defendants were entitled to use such methods to prove that they overpaid Garden City because of its alleged submission of invalid claims.
Although the motion justice improperly found the agreements in question to be unambiguous, I nevertheless conclude that the court properly granted summary judgment to Garden City. I do so because the defendants did not satisfy their burden of showing the existence of a genuine issue of material fact about the validity of the statistical-sampling methods they used to justify their actions vis-a-vis the alleged over-*550payments. See Thibodeau v. Metropolitan Property & Liability Insurance Co., 682 A.2d 474, 475 (R.I.1996) (per curiam) (recognizing that this Court can affirm the grant of summary judgment on a basis not relied on by the court below if supported by law and the record). Consequently, I would hold that the court properly granted summary judgment against the defendants, albeit for different reasons than those relied upon by the majority of my colleagues.
. Rule 702 of the Rhode Island Rules of Evidence provides: "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of fact or opinion.”
. Rule 703 of the Rhode Island Rules of Evidence provides:
"An experts opinion may be based on a hypothetical question, facts or data perceived by the expert at or before the hearing, or facts or data in evidence. If of a type reasonably and customarily relied upon by experts in the particular field in forming opinions upon the subject, the underlying facts or data shall be admissible without testimony from the primary source.”