¶37 (dissenting) — Pursuant to legislative mandate, the Department of Social and Health Services (DSHS) developed the comprehensive assessment reporting evaluation (CARE) tool. The CARE tool provides a mechanism for uniformly assessing functional disability and allocating state-paid personal care services to individuals seeking such services. One component of the CARE tool, the shared living rule,9 adjusts the allocation of services when an individual lives with his or her paid caregiver. The majority concludes that the shared living rule violates the federal Medicaid comparability provision, which requires a state to make available to an individual the same “amount, duration, [and] scope [of] medical assistance” as it makes available “to any other such individual.” 42 U.S.C. § 1396a(a)(10)(B)(i). I disagree.
Fairhurst, J.¶38 First, I disagree with the majority’s position that DSHS should be accorded no administrative deference in our review of the shared living rule. Unlike the majority, I do not believe that the comparability provision clearly indicates Congress’s intent with respect to the specific question before us. Properly framed, that question is — what factors may be considered when assessing the relative needs of individuals seeking Medicaid assistance? On this question the comparability provision is silent. Given that silence, I would accord DSHS some measure of deference based on its expertise in administering the State’s Medicaid program.
*304¶39 Second, I disagree with the majority’s claim that the shared living rule is invalid because “ ‘presum [ing]’ some recipients need fewer hours of care without individualized determination violates the comparability requirement.” Majority at 300. While I agree that the shared living rule operates as a presumption, it is just one of the many presumptions in the CARE tool. Furthermore, properly understood, the CARE tool does not produce any individualized determinations of the need for services.
¶40 Accepting the majority’s premise that the shared living rule violates the comparability provision because it reduces services without an individualized determination establishes a sweeping precedent that could affect not only the CARE tool but the way all public assistance benefits are allocated. The majority’s reasoning does not distinguish a principled basis upon which this court should substitute our judgment for that of DSHS in this instance with respect to the shared living rule, but refrain from doing so with respect to other similar presumptions in the CARE tool. As a properly promulgated administrative rule, the shared living rule is presumptively valid and should be upheld if it is reasonably consistent with the comparability provision. In my opinion, because the majority has not demonstrated a principled basis for distinguishing between the shared living rule and other CARE tool rules, the majority has not overcome that presumption of validity. This conclusion is strengthened by granting even the most minimal deference to DSHS’s expertise. I would hold that the shared living rule does not violate the comparability provision. Accordingly, I respectfully dissent.
ANALYSIS
A. Administrative Deference
¶41 The majority concludes, almost without discussion, that DSHS should be accorded no deference to its interpretation of the comparability provision. Majority at 297. I disagree. Whether DSHS should be accorded any deference *305requires a more robust analysis of the comparability provision than the majority puts forth. While I agree that “the comparability provision requires comparable services when individuals have comparable needs,” majority at 298, the needs of individuals can be compared only after they have been assessed and quantified. Because the comparability provision is silent on that specific question, Chevron deference10 is warranted to the reasonable interpretation of the provision by the federal agency charged with administering it. That agency has determined that states may consider shared living circumstances in assessing needs and allocating services. Pursuant to state legislative mandate to ensure a uniform system for assessing needs and allocating services, DSHS developed the CARE tool and included a component that considers an individual’s shared living circumstances. While not required to consider such circumstances, DSHS in its expertise determined that doing so was appropriate. That determination is entitled to some measure of administrative deference from this court.
¶42 The majority suggests that no deference is warranted to DSHS “because the Medicaid comparability provision is specific in demonstrating Congress’ intent to provide comparable services to similarly situated recipients.” Majority at 297 (emphasis added). The comparability provision mandates simply that the medical assistance that a state makes available to an individual under its Medicaid plan shall not be less “in amount, duration, or scope” than that made available to others who qualify for medical assistance under that plan. 1142 U.S.C. § 1396a(a)(10)(B)(i). *306The comparability provision does not mandate that a state provide all qualifying individuals with identical quantities of services, regardless of their needs for services. Such a requirement would defy logic. Rather, as the majority agrees, “the comparability provision requires comparable services [only where] individuals have comparable needs.” Majority at 298. However, what the majority fails to note is that the comparability provision is silent as to how states should quantify the relative needs of those to whom it must provide comparable services.
¶43 The Centers for Medicare & Medicaid Services (CMS), the federal agency charged with administering the Medicaid program,12 has promulgated regulations interpreting the comparability provision. When a court reviews a federal statute, “if the statute is silent or ambiguous with respect to the specific issue,” and the federal agency administering the statute has promulgated a regulation construing it, the “court may not substitute its own construction... for a reasonable interpretation made by” the agency. Chevron U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 842-44, 104 S. Ct. 2778, 81 L. Ed. 2d 694 (1984). One CMS regulation interpreting the comparability provision essentially paraphrases it.13 A second CMS regulation interpreting sufficiency of “amount, duration, and scope” of services provides that, while “[e]ach service must be sufficient in amount, duration, and scope to reasonably achieve its purpose, . . . [t]he agency may place appropriate limits *307on a service based on such criteria as . . . utilization control procedures.” 42 C.F.R. § 440.230(a)(2)(b), (d). By clarifying that a state may appropriately limit its provision of a service, CMS indicates that such service limitations do not per se violate the comparability provision. Using the language “on such criteria as” indicates that “utilization control procedures” are illustrative, not exhaustive, of the type of criteria by which a state may permissibly limit the provision of services.
¶44 CMS has provided further guidance specifically addressing a state’s provision of Medicaid state-paid personal care services in shared living situations. “When an agency construes its own regulations, [judicial] deference is particularly appropriate, and even more appropriate where, as here, [the court] consider [s] a small corner of a labyrinthine statute.” Skandalis v. Rowe, 14 F.3d 173, 178 (2d Cir. 1994) (citations omitted) (deferring to interpretation of Medicaid statutes and regulations advanced by the secretary of DSHS). In its guide to the provision of Medicaid home care services, CMS states that, to be Medicaid-reimbursable, “services must address the beneficiary’s needs. This means that services cannot be furnished if they principally benefit the ‘family unit.’ ” U.S. Dep’t of Health & Human Servs., Understanding Medicaid Home and Community Services: A Primer 131 (Oct. 2000) (located in Rule Making File, Gasper v. Dep’t of Soc. & Health Servs., No. 04-2-01400-7, at SHS-0005 to 06). States may take into account the amount of informal care available to an individual. Id. Consideration may also be given to “the kinds of household tasks family members typically expect to share ... when they live in the same household.” Id.
¶45 Because the comparability provision is silent on the specific question here — what factors may be considered when assessing the relative needs of individuals seeking Medicaid assistance — I believe that the CMS regulations and guidance interpreting the provision should be accorded this court’s deference. Thus, as CMS clarifies, a state does not violate the comparability provision by giving appropri*308ate consideration to individuals’ shared living circumstances when allocating state-paid personal care services.
¶46 At the state level, this court interprets the meaning of statutes de novo and may substitute its interpretation for that of an agency, but if the statute is ambiguous, “ ‘[wjhere a statute is within [an] agency’s special expertise, the agency’s interpretation is accorded great weight.’ ” Port of Seattle v. Pollution Control Hearings Bd., 151 Wn.2d 568, 593, 90 P.3d 659 (2004) (alterations in original) (quoting Postema v. Pollution Control Hearings Bd., 142 Wn.2d 68, 77, 11 P.3d 726 (2000)).
¶47 The legislature expressly charged DSHS with developing a uniform system for comprehensively assessing the need of functionally disabled individuals for medical services. See RCW 74.09.520(4); RCW 74.39.005(2). In response, DSHS developed the CARE tool, through which it evaluates eligibility for and allocates state-paid personal care services to functionally disabled individuals. WAC 388-106-0005 to -0130.14 DSHS incorporated into the CARE tool a formula for adjusting an individual’s allocation of state-paid personal care services to reflect the amount of informal support that individual receives. Built into the informal support formula is consideration of the individual’s shared living circumstances. Given that CMS’s authoritative interpretation of the comparability provision permits consideration of such circumstances, I believe that DSHS’s decision to consider shared living circumstances and its mechanism for such consideration is entitled to some measure of administrative deference. However, administrative deference, while warranted, does not itself resolve whether the shared living rule violates the comparability provision, the question to which I now turn.
*309B. Shared Living Rule Presumption
¶48 “[T]he question is whether DSHS exceeded its statutory authority by promulgating a rule that conflicts with federal law, namely [the shared living rule].” Majority at 295. “ ‘[Administrative rules adopted pursuant to a legislative grant of authority are presumed to be valid and should be upheld on judicial review if they are reasonably consistent with the statute being implemented.’ ” Campbell v. Dep’t of Soc. & Health Servs., 150 Wn.2d 881, 892, 83 P.3d 999 (2004) (alteration in original) (quoting Fahn v. Cowlitz County, 93 Wn.2d 368, 374, 610 P.2d 857, 621 P.2d 1293 (1980)). The burden of demonstrating the invalidity of an agency rule is on the party asserting the invalidity. RCW 34.05.570(l)(a); Wash. Pub. Ports Ass’n v. Dep’t of Revenue, 148 Wn.2d 637, 645, 62 P.3d 462 (2003).
¶49 The majority reasons that the shared living rule violates the comparability provision because, as an irrebuttable presumption, the rule operates without making an individualized determination of each individual’s actual need for services. Majority at 296-301. However, as I discuss below, the shared living rule is just one of the many irrebuttable presumptions in the CARE tool, a tool that does not make any individualized determinations of actual need. The majority does not articulate a principled basis upon which this court should substitute our judgment for that of DSHS in this instance with respect to the shared living rule but refrain from doing so with respect to other presumptions in the CARE tool. In my opinion, absent that principled basis, the majority has not demonstrated that the rule’s presumptive validity is overcome.
¶50 The majority states that the shared living rule “establishes an irrebuttable presumption that the recipient’s need for assistance is met for instrumental activities of daily living (IADL) of meal preparation, housekeeping, shopping, and wood supply.” Majority at 295. I agree that the shared living rule “establishes an irrebuttable presumption.” However, the majority implies that in this *310respect the shared living rule is unique and therefore suspect. Unlike the majority, I recognize that the CARE tool is built on a framework of irrebuttable presumptions, of which the shared living rule is merely one.
¶51 DSHS developed the CARE tool pursuant to a legislative mandate that DSHS “[e]nsure that functional ability shall be the determining factor in defining long-term care service needs and that these needs will be determined by a uniform system for comprehensively assessing functional disability.” RCW 74.39.005(2) (emphasis added). Each functionally disabled individual is unique in both disabilities and need for long-term care services. Nevertheless, DSHS was charged with developing a uniform system for assessing functional disability to support the equitable allocation of the State’s all-too-limited resources across the pool of eligible recipients. The price of uniformity is that fit may be imprecise in a particular individual’s circumstances.
¶52 In a CARE evaluation, an individual is assessed in each of four areas: “[cjognitive performance,” “[c]linical complexity,” “[m]ood/behaviors symptoms,” and ability to perform “[ajctivities of daily living (ADLs).” WAC 388-106--0085. Cognitive performance is scored from “zero (intact) to six (very severe impairment).” WAC 388-106-0090. Clinical complexity and mood/behaviors are each answered either yes or no. WAC 388-106-0095, -0100. Ability to perform ADLs is scored from 0 to 28. WAC 388-106-0105. Using an individual’s scores in each of the four areas, the CARE tool assigns the individual to one of 14 classification groups.15 WAC 388-106-0125. By administrative rule, DSHS has assigned to each classification group a base number of *311hours per month for personal care services, ranging from 29 to 420 hours. WAC 388-106-0125.
¶53 Assigning an individual to a classification group is only the initial step in determining how many hours of state-paid personal care services per month the state can provide to an individual. WAC 388-106-0130. DSHS then “deducts from the base hours to account for informal supports.”16,17 WAC 388-106-0130(2). The adjustment is based upon “the amount of [informal] assistance available to meet [the recipient’s] needs” in performing each of nine ADLs18 and four IADLs19 during the seven days immediately preceding the assessment. WAC 388-106-0130(2)(a). For each of the ADLs and IADLs, the available informal support is deemed to have not met, partially met,20 or fully met the individual’s need. As with other components in the CARE tool, the gathered information is translated into scores.
¶54 The shared living rule operates within the context of the deduction for informal support — where an individual *312lives together with his or her paid caregiver,21 the individual’s need for housekeeping, essential shopping, and meal preparation are presumed to be met.22 As the majority states, the shared living rule “was implemented on the theory that if caregivers must clean their own houses, go shopping, and cook meals for their own benefit, certain duplication of efforts are presumed, and ... a state should not pay for those tasks that benefit the entire household.” Majority at 292; WAC 388-106-0130(2)(a). A mathematical formula translates an individual’s total score for informal support, including the scores determined by the presumption of the shared living rule, into a percentage by which the base number of hours is reduced. WAC 388-106-0130(2)(b). This final adjusted amount, the product of the complete CARE assessment, represents the number of state-paid personal care service hours per month for which the individual qualifies.
¶55 The enterprise of reducing the infinite variety of a diverse population to a set of numeric scores and yes or no answers intrinsically requires using irrebuttable presumptions. For example, DSHS has determined by rule that an individual is clinically complex only if he or she has one of a designated list of conditions in combination with the ADL score required for that particular condition. WAC 388-106--0095. An individual with cerebral palsy and an ADL score of more than 14 is deemed clinically complex, while with a score of 14 or less, he or she is not. Id. By contrast, an individual who requires dialysis need only have an ADL score of more than 10 to be deemed clinically complex. Id. An individual may request that DSHS review factual error in an assessment, e.g., dialysis is required where the *313assessment says it is not. But an individual cannot successfully argue that, in her particular case, having cerebral palsy plus an ADL score of 12 makes her clinically complex. Each determination that a select condition and a requisite ADL score is clinically complex or not is an irrebuttable presumption.
f 56 I agree with the majority that the shared living rule operates as an irrebutable presumption, but it is just one of many irrebutable presumptions that comprise the CARE tool. Irrebuttable presumptions delineate the 14 classification groups, provide the framework that translates assessment scores into those groups, and allocate the interim base number of hours to each group. The nature of a presumption is that it will not match precisely the particular circumstances of every individual to whom it is applied. But it is only through the operation of a framework of presumptions that DSHS is able to create a “uniform system for comprehensively assessing functional disability.” RCW 74.39.005(2) (emphasis added). The majority’s implication that the shared living rule is particularly suspect because it is an irrebutable presumption does not withstand scrutiny.
¶57 Having established that the shared living rule is an irrebuttable presumption, the majority then claims that the rule is invalid because “[t]o ‘presume’ some recipients need fewer hours of care without individualized determination violates the comparability requirement.” Majority at 300. This claim rests on the majority’s inaccurate suggestion that “DSHS decided on individualized determinations of public assistance benefits for this categorically needy group of Medicaid recipients,” only to deny individualized determinations to the respondents and others like them by applying the shared living rule. Id. at 299. In fact, the respondents are treated in the same manner as other Medicaid recipients because no recipient is individually assessed as to his or her need for housekeeping, shopping, and meal preparation.
¶58 Contrary to the majority’s claim that “[a] recipient who does not live with a caregiver is assessed an amount *314needed for meal preparation, housekeeping, and shopping,” but a recipient who does live with a caregiver is assessed with different criteria, id. at 300, the base number of hours allocated to each of the 14 classification groups incorporates assistance with these tasks. All recipients, whether they do or do not live with their caregivers, uniformly receive the interim base hour allocation assigned to their classification groups. Then that base number of hours is reduced in consideration of the informal support that an individual receives to meet IADL and ADL needs. DSHS never evaluates how many hours of assistance an individual actually requires to meet his or her IADL and ADL needs.
¶59 The majority finds it significant that the shared living rule “reduces” the initial allocation of a base number of hours, stating that “[o]nce a person is assessed to require and receive a certain number of care hours, the assessment cannot be reduced absent a specific showing that fewer hours are required.” Id. at 300. However, the base number of hours is not a number of hours that an individual has been specifically assessed to require — the base number is a nonspecific, interim allocation associated with the classification group, which may or may not be sufficient to meet the individual’s actual needs. Additionally, the informal support adjustment likewise “reduces” the base number without a “specific showing that fewer hours are required.” For example, the determination that an individual’s needs are met between one-half and three-fourths of the time results in a standard percentage reduction of the base number of hours. Just as there is no initial determination of how many hours are actually required to meet the individual’s needs absent informal support, there is no subsequent evaluation of whether the reduced hours are sufficient to meet the need that is unmet by informal support. Finally, the fact that the shared living rule “reduces” the base number of hours is an artifact of how the CARE tool is programmed. The CARE tool could just as easily have been designed to allocate to each classification group a lower base number of hours that would then be adjusted upward *315depending on access to informal support, living circumstances, and other factors.
¶60 As part of the informal support evaluation, if an individual lives with a paid caregiver, the shared living rule presumes that housekeeping, shopping, and meal preparation needs are fully met. On the other hand, no adjustment is made for informal support that the paid caregiver provides with ADL needs, notwithstanding that such support could be substantial, especially where the paid caregiver is also a family member or friend of the recipient. The majority’s claim that “DSHS’s refusal to consider the individual needs of [the respondents] for assistance with housekeeping, shopping, and meal preparation violates their right to be treated in the same manner as all other categorically needy Medicaid recipients who are individually assessed for the same needs” betrays the majority’s fundamental misunderstanding of how the CARE tool operates. Majority at 299. The CARE tool does not operate by assessing each individual’s particular need for assistance. The entire CARE process is based on presumptions and approximations, regardless of whether an individual does or does not live with his or her caregiver.
¶61 The majority even acknowledges that “DSHS may use the CARE assessment program to initially classify, rate, and determine a recipient’s level of need because this process is consistent with the Medicaid program’s purpose.” Id. at 299. In this the majority seemingly endorses the need to employ the CARE tool’s presumption-based system. However, the majority then continues, “DSHS violates the comparability requirement when it reduces a recipient’s benefits based on a consideration other than the recipient’s actual need.” Id. (emphasis added). The CARE tool does not — cannot—allocate state-paid personal care services based on individuals’ actual need. DSHS is charged with fairly allocating an all-too-limited pool of resources across a population of individuals whose needs far exceed what the State is able to provide. Each individual is unique, with unique abilities, disabilities, medical conditions, and cir*316cumstances. Given the mandate to develop a “uniform system for comprehensively assessing functional disability,” RCW 74.39.005(2), DSHS is constrained to proceed by formulating a framework of presumption-defined determinations, which it has encapsulated in the CARE tool.
CONCLUSION
¶62 Ultimately, the majority invalidates the shared living rule “to the extent that it presumes certain needs of the recipient are met without an individualized determination and the presumption results in an automatic 15 percent reduction in the recipient’s assessed number of allotted care hours based only on the fact that the recipient lives with a caregiver.” Majority at 300. This conclusion describes how the shared living rule operates, but not why that mode of operation renders the shared living rule invalid.
¶63 The majority’s reasoning does not distinguish a principled basis upon which this court should substitute our judgment for that of DSHS in this instance with respect to the shared living rule, but refrain from doing so with respect to other presumptions in the CARE tool. As a properly promulgated administrative rule, the shared living rule is presumptively valid and should be upheld if it is reasonably consistent with the comparability provision. In my opinion, because the majority has not demonstrated a principled basis for distinguishing between the shared living rule and other CARE tool rules, the majority has not overcome the rule’s presumptive validity. This conclusion is strengthened by granting even the most minimal deference to DSHS’s expertise. Therefore, I would hold that the shared living rule does not violate the comparability provision. Accordingly, I respectfully dissent.
Madsen and Bridge, JJ., concur with Fairhurst, J.
Reconsideration denied August 16, 2007.
Former WAC 388-72A-0095 (2004), amended and recodified at WAC 388-106--0130(3)(b) (2005).
Chevron U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 842-44, 104 S. Ct. 2778, 81 L. Ed. 2d 694 (1984).
The comparability provision requires that a state Medicaid plan must provide:
(B) that the medical assistance made available to any individual described in subparagraph (A)—
(i) shall not be less in amount, duration, or scope than the medical assistance made available to any other such individual, and
(ii) shall not be less in amount, duration, or scope than the medical assistance made available to individuals not described in subparagraph (A).
*30642 U.S.C. § 1396a(a)(10)(B) (emphasis added).
Subparagraph A defines the categories of individuals to whom a state must provide medical assistance as part of its Medicaid plan, 42 U.S.C. § 1396a(a)(10)(A)(i), and to whom a state may provide assistance if it chooses, 42 U.S.C. § 1396a(a)(10)(A)(ii).
Pharm. Research & Mfrs. of Am. v. Walsh, 538 U.S. 644, 651 n.3, 123 S. Ct. 1855, 155 L. Ed. 2d 889 (2003).
42 C.F.K. § 440.240 provides:
(b) The plan must provide that the services available to any individual in the following groups are equal in amount, duration, and scope for all recipients within the group:
(1) The categorically needy.
(2) A covered medically needy group.
The WAC provisions dealing with long-term care services, including the CARE assessment tool, former chapter 388-72A WAC (2004), were recodified at chapter 388-106 WAC. Wash. St. Reg. 05-11-082 (June 17,2005). This opinion cites to the current WAC provisions, which are substantially the same as the provisions in place when respondents were evaluated.
The majority states that the CARE “scores are put into a formula that calculates the individual’s base assistance level in hours of care and places the individual into one of 14 residential classification groups.” Majority at 291. This explanation suggests, inaccurately, that a base number of required care hours is calculated for each individual directly from that individual’s CARE scores, through an individualized determination process. To the contrary, CARE scores are used to assign an individual to one of the 14 groups. Each group has been designated a base number of hours. That base number is then adjusted depending on the individual’s circumstances.
An “ ‘[finformal support’ ” is “a person or resource that is available to provide assistance without home and community program funding.” WAC 388-106-0010.
DSHS may also add hours based on an individual’s living environment, in consideration of the individual’s distance from essential services (laundry, shopping) and exclusive reliance on wood for heat. WAC 388-106-0130(4).
The nine ADLs assessed for the availability of informal support are (1) self-administration of medications, (2) bed mobility, (3) transfer, (4) walk in room, (5) eating, (6) toilet use, (7) dressing, (8) personal hygiene, and (9) bathing. WAC 388-106-0010. This list shares ADLs in common with, but is not identical to, the activities considered in assessing an individual’s ADL score, used in assigning an individual to a classification group. WAC 388-106-0105.
The four IADLs assessed are meal preparation, ordinary housework (including laundry), essential shopping, and travel to medical. WAC 388-106-0130(2); see also WAC 388-106-0010 (defining “ ‘[ojrdinary housework’ ” as “doing dishes, dusting, making bed, tidying up, laundry”).
The assessment of partially met is further subdivided into four quartiles of (1) less than one-fourth of the time, (2) between one-fourth and one-half of the time, (3) between one-half and three-fourths of the time, and (4) more than three-fourths of the time. WAC 388-106-0130(2).
The shared living rule also applies if an individual lives together with another individual receiving state-paid personal services. WAC 388-106-0130(3)(a).
The majority suggests that “[i]f the recipient lives with a caregiver, a second formula is applied to reduce the number of care hours for which the recipient qualifies.” Majority at 292. This is inaccurate. The shared living rule is applied within the adjustment for informal supports, using the same formula. WAC 388-106-0130.