OPINION
¶ 1 An Arizona administrative rule provides that a physician should rate an injured worker’s impairment using standards set forth in the “most recent edition” of the American Medical Association Guides to the Evaluation of Permanent Impairment (AMA Guides). Ariz. Admin. Code (A.A.C.) R20-5113(B). We must determine whether “most recent edition” refers to the edition that was most recent when the Rule was promulgated (the Fifth Edition) or the latest edition existing when the claimant’s impairment was rated (in this case, the Sixth Edition). For the reasons set forth below, we hold that A.A.C. R20-5-113(B) refers to the edition most recently published before the claimant’s impairment is rated and that this reference does not constitute an improper delegation of legislative authority.
I. FACTUAL AND PROCEDURAL BACKGROUND
¶ 2 Jesus Gutierrez injured his back in 2007 while working for Masterson & Clark Framing. His claim for workers’ compensation benefits was accepted and he received medical treatment. The treating physician later released Gutierrez to return to work with physical restrictions. Concluding that Gutierrez was not permanently impaired, the insurance carrier closed the claim. Gutierrez requested a hearing to challenge the “no impairment” determination.
¶3 At the Industrial Commission of Arizona (ICA) hearings, the Administrative Law Judge (ALJ) heard testimony from two physicians: Gutierrez’s treating orthopedic surgeon and a doctor presented by the carrier. Relying on the Fifth Edition of the AMA Guides, Gutierrez’s expert testified that Gutierrez suffered from a resolved lumbar radiculopathy. He rated Gutierrez’s injury as a five percent permanent impairment. Relying on the Sixth Edition, which provides no permanent impairment rating for a resolved radiculopathy, the carrier’s expert opined that Gutierrez had no ratable permanent impairment.
¶ 4 Based on the latter testimony, the ALJ found that the insurance carrier did not err in closing Gutierrez’s claim. On special action review, the court of appeals affirmed.
Gutierrez v. Indus. Comm’n,
II. DISCUSSION
A. Interpreting “most recent edition”
¶ 5 The administrative rule at issue, A.A.C. R20-5-113(B), provides as follows:
When a physician discharges a claimant from treatment, the physician [s]hall determine whether the claimant has sustained any impairment of function resulting from the industrial injury. The physician should rate the percentage of impairment using the standards for the evaluation of permanent impairment as published by the most recent edition of the American Medical Association in Guides to the Evaluation of Permanent Impairment, if applicable.
We interpret the provisions de novo, “applying] the same rules in construing both statutes and rules.”
Smith v. Ariz. Citizens Clean Elections Comm’n,
¶ 6 The question presented is which edition of the AMA Guides the Rule means by its reference to the “most recent edition.” The term “most recent” is commonly understood as giving perpetual duration to a statute or rule that relies on changing facts and new developments or would otherwise require frequent updating.
Cf. City of Phoenix v. Superior Court (Ariz. State Hosp.),
¶ 7 This interpretation comports with the use of the phrase “most recent” in other rules and statutes. Several statutes and rales require submission or retention of “most recent” documents such as financial statements or receipts. See, e.g., A.R.S. § 3-609(A) (2002) (requiring submission of financial statements for the “most recent complete fiscal year”); A.A.C. R20-5-203(A)(3) (requiring submission of the “most recent certified annual financial statement”); A.A.C. R20-2-707(E) (requiring retention of receipts for the “three most recent deliveries of ... motor fuel”). It would frustrate the purpose of those provisions to require submission or retention of outdated documents (those existing when the rule or statute became effective) despite the passage of time and the existence of more current documents. The operation of several other statutes depends on data from the “most recent” census. See, e.g., A.R.S. § 1-215(31) (2002 & Supp.2010) (defining “population” based on the “most recent United States decennial census”); A.R.S. §§ 5-110(1) (2002); 9-132 (2008); 11-254.02(A) (2001); 12-284.03 (2003 & Supp. 2010); 13-3826 (2010); 42-16153(A) (2006 & Supp.2010); 48-3620(E) (2004 & Supp.2010). The legislature undoubtedly did not intend to require reliance on stale census data despite the completion of new decennial censuses. Provisions that use the term “most recent” therefore anticipate and incorporate changes and developments, even those that occur after the effective date of a statute or rale.
¶ 8 Historical practice of the ICA also suggests that “most recent edition” means the newest version extant when a claimant’s impairment is rated. The prior version of the Rule, much like the current one, recommended that impairment be rated according to the “standards for the evaluation of permanent impairment as published by the American Medical Association in Guides to the Evaluation of Permanent Impairment, if applicable.” 7 Ariz. Admin. Reg. 25 (Jan. 5, 2001). Although the earlier version of the Rule did not include the words “most recent edition,” parties and courts regularly referred to each new edition as it became available.
See, e.g., Simpson v. Indus. Comm’n,
¶ 9 This interpretation also leads to the more sensible result. Reference to the current version of the AMA Guides allows the doctor to consider the latest medical developments when determining impairment. Gutierrez’s reading of “most recent edition,” in contrast, would require the physician to look up A.A.C. R20-5-113(B), determine its effective date, find which version of the AMA Guides was the “most recent edition” when the Rule became effective, and possibly rely on an outdated, superseded version of the Guides when rating impairment. Reading the Rule as referring to the newest edition of the Guides precludes this impractical result and allows consideration of medical advancements.
See State v. Estrada,
B. Delegation of legislative power
¶ 10 Gutierrez argues that if A.A.C. R20-5-113(B) refers to the version of the AMA Guides “most recent” when the claimant’s impairment is rated, the Rule unconstitutionally delegates authority to the AMA to set the standards physicians must use to rate *398 impairment. He contends that although the Arizona Legislature delegated to the ICA the power to adopt rules regarding the presentation of compensation claims, see A.R.S. § 23-921(B) (1995), it could not delegate rulemaking authority to the AMA or empower the ICA to do so.
¶ 11 An improper delegation of legislative authority may occur when a statute (and, by implication, a rule) incorporates later-developed standards not promulgated by the Legislature or an Arizona agency.
See State v. Williams,
¶ 12 The text of A.A.C. R20-5-113(B) indicates that the use of the AMA Guides in rating impairment is discretionary. The Rule provides that, in determining a claimant’s impairment, the physician “should” use the AMA Guides “if applicable.” Use of these permissive qualifiers, particularly following use of the mandatory term “shall” in the preceding sentence, reveals that the physician is not required to apply the AMA Guides.
See City of Mesa v. Salt River Project Agric. Improvement & Power Dist.,
¶ 13 This Court has previously recognized that the use of the AMA Guides is discretionary and that impairment may be established by evidence other than the AMA Guides.
1
In W.A.
Krueger Co. v. Industrial Commission of Arizona,
we observed that “[t]he AMA Guides are not to be blindly applied regardless of a claimant’s actual physical condition. Rather, their purpose is to serve as a
guideline
in rating an impairment and [they] are valid when the stated percentage ‘truly reflects the claimant’s loss.’ ”
¶ 14 Because physicians are not bound to apply the AMA Guides when rating impairment, the reference to later-developed editions of the AMA Guides in A.A.C. R20-5113(B) does not constitute an improper delegation of legislative power.
III. CONCLUSION
¶ 15 For the reasons set forth above, we affirm ¶¶ 1-15 of the opinion of the court of appeals 2 and affirm the award and decision of the ICA.
Notes
. These cases interpret the previous version of A.A.C. R20-5-113(B) (formerly A.A.C. R20-5113(D)), which was amended to the current form in 2001. Nothing in the 2001 amendment changed whether use of the AMA Guides is mandatory or discretionary.
. Although we affirm the opinion of the court of appeals, we do not adopt the suggestion in ¶ 16 and footnote five that the American Medical Association is, for separation of powers purposes, analogous to a state administrative agency.
Further, the Court declined to review the court of appeals’ ruling that use of the Sixth Edition does not violate article 18, section 8, of the Arizona Constitution, and therefore our opinion reflects neither approval nor disapproval of ¶¶ 17-20 of the opinion.
