concurring in part and dissenting in part:
I agree with Part II of the majority opinion, explicating the policymaking authority of the Department of Revenue, determining that the “20% rule” cannot be used in administrative driver’s license revocation proceedings absent compliance with the rulemaking procedures of section 24-4-103, 10A C.R.S. (1988), and concluding that the hearing officer erred by applying the “20% rule” to resolve the conflicting results of the two intoxilyzer tests involved in this case. However, I respectfully dissent from Part III of the majority opinion. In my view, the hearing officer acted in an arbitrary and capricious manner by summarily applying the “20% rule” and by failing to evaluate by appropriate standards the discrepancy between the two test results. Accordingly, I would remand to the court of appeals with directions to return the case to the Department of Revenue for a determination of whether, applying the proper standards, Robinson’s blood-alcohol content was 0.15 or higher.
In administrative revocation proceedings, judicial review of hearing officer decisions is limited to an evaluation of whether the Department of Revenue “exceeded its constitutional or statutory authority, made an erroneous interpretation of the law, acted in an arbitrary and capricious manner, or made a determination which is unsupported by the evidence in the record.” § 42-2-122.1(9)(b), 17 C.R.S. (1984). “Where conflicting evidence is presented in an administrative hearing, the credibility of witnesses and the weight to be given their testimony are decisions within the province of the agency.” Charnes v. Lobato, 743 P.2d 27, 32 (Colo.1987); see also G & G Trucking Co. v. Public Util. Comm’n, 745 P.2d 211, 216 (Colo.1987); Acme Delivery Serv. v. Cargo Freight Sys., 704 P.2d 839, 843 (Colo.1985). When acting in its capacity as the trier of fact, however, an administrative agency is entitled to deference only when it applies the correct criteria in resolving evidentiary conflicts. See Gonzales v. Industrial Comm’n, 740 P.2d 999, 1001 (Colo.1987). Therefore, inquiry into whether the agency applied the proper principles of law in evaluating the evidence before it is not forestalled simply because the record supports the agency’s ultimate findings. Id.; see also Electric Power Research Inst. v. City and County of Denver, 737 P.2d 822, 825-26 (Colo.1987).
In Lobato, we upheld a hearing officer’s exercise of discretion in determining that although the conflicting results of intoxi-lyzer tests weighed evenly, the preponderance of the evidence issue should be resolved in favor of the test given nearer to the time that the offense of driving under the influence of alcohol was committed. Lobato, 743 P.2d at 30-34. In reaching this conclusion we noted that
*70[m]any factors may enter into a hearing officer’s decision that one test is more reliable than another, including but not limited to such variables as the equipment and chemical standards used, the experience of each witness, and the circumstances surrounding a particular test. The determination as to which test result has greater reliability and deserves greater weight is within the agency’s discretion and not an issue to be analyzed on appellate review.
Lobato, 743 P.2d at 33.
In the instant case, the majority opinion concludes that despite the hearing officer’s erroneous application of the “20% rule,” there was sufficient evidence in the record upon which the hearing officer could make a determination that Robinson drove a vehicle with at least a 0.15 blood-alcohol content. In my opinion, the record contains no indication that the hearing officer based his determination on anything other than the results of the two intoxilyzer tests, and the “20% rule.” Indeed, the transcript of the hearing officer’s ruling on the blood-alcohol content issue consists of only a few remarks directed toward the discrepancy between the two intoxilyzer tests. These remarks reveal that the hearing officer found that the results of the second intoxilyzer test supported rather than refuted those of the first test. The hearing officer clearly reached this conclusion by operation of the “20% rule.” See maj. op. at p. 64 (quoting full text of hearing officer’s remarks on the blood-alcohol content issue).
We have no way of knowing on the basis of this record whether the hearing officer would have reached the same ultimate result without the benefit of the “20% rule.” Cf. Salt River Project v. United States, 762 F.2d 1053, 1060-61 n. 8 (D.C.Cir.1985) (affirming agency action without remanding where agency clearly would have reached the same ultimate result had it relied on only those findings that were not erroneous). Nothing in the record suggests that the hearing officer gave any consideration to the types of factors deemed appropriate in Lobato for resolving conflicts between intoxilyzer test results, or to any other evidence concerning blood-alcohol content.1 Consequently, it is a usurpation of the agency’s role for this court to assess credibility and weigh testimony or other evidence in reaching a determination that the record supports a finding by a preponderance of the evidence that Robinson’s blood-alcohol content was 0.15 or higher. I would therefore hold that the hearing officer’s determination to revoke Robinson’s license was arbitrary and capricious and remand to the court of appeals with directions to return the case to the Department of Revenue for reconsideration.
ERICKSON, J., joins in this concurrence and dissent.
. The transcript of the administrative hearing contains a brief discussion by the hearing officer of the "matter of the certification of the [intoxilyzer] device and the operator.” However, this finding was apparently entered in response to Robinson's contention that the state failed to present evidence that the intoxilyzer used to conduct the first test was working properly, was operated correctly, and was properly registered and certified by the State of Colorado as required by various Colorado Department of Health Regulations. This finding does not in any way address the comparative reliability of the two tests.