This appeal presents the question of whether Respondent South Carolina Department of Health and Human Services and its agent, the South Carolina Department of Disabilities and Special Needs (DDSN), “properly ceased Mental Retardation/Related Disability services to”1 Appellant Jane Doe, a twenty-eight-year-old woman with undeniable cognitive and adaptive deficits. Based on a purported legal standard that the “onset of Mental Retardation must be before the age of eighteen (18) years according to accepted psychological doctrine[,]” the Hearing Officer concluded Doe was not mentally *64retarded. The Administrative Law Court (ALC) affirmed this legal determination, as well as the Hearing Officer’s factual findings. Because the decision of the Hearing Officer and ALC is controlled by an error of law, we reverse and remand.
I.
BACKGROUND
A.
Medicaid is a program through which the federal government, through the Social Security Administration (SSA), provides financial assistance to states so that they may furnish medical care to needy individuals. Wilder v. Virginia Hosp. Assoc., 496 U.S. 498, 502, 110 S.Ct. 2510, 110 L.Ed.2d 455 (1990). Participation in the program is voluntary; however, participating states must comply with requirements imposed by the Medicaid Act and related regulations. Id. To receive federal funding, a state must submit and have approved a “plan for medical assistance” that describes the nature and scope of the state’s Medicaid program. Id. A state’s plan must provide medical services for the “categorically needy” and, among other things, must provide services under any option to all Medicaid beneficiaries for whom they are medically necessary. See 42 U.S.C. § 1396a(a)(l), (a)(10)(A)(i), (a)(10)(B) (2006); Pharm. Research & Mfrs. of Am. v. Walsh, 538 U.S. 644, 651 n. 4, 123 S.Ct. 1855, 155 L.Ed.2d 889 (2003).
Supplemental Security Income (SSI), which is Title XVI of the Social Security Act, provides support for those who are aged, blind, or disabled and subsist on a limited income. 20 C.F.R. § 416.1100 (2011). To receive SSI, a recipient must have a disability such that he cannot accomplish “substantial gainful activity” for profit. 20 C.F.R. § 416.905 (2011). Federal regulations provide that an individual found eligible for SSI is automatically enrolled in the Medicaid program and is entitled to the base level of benefits the state must provide to all Medicaid beneficiaries. 42 U.S.C. § 1396a(a)(10)(A)(i)(II) (2006); 42 C.F.R. § 435.909(b)(1) (2010); Pharm. Research, 538 U.S. at 651 n. 4, 123 S.Ct. 1855.
Since 1981, Medicaid has provided funding for state-run home and community based services (“HCBS”) through a *65waiver program. For Medicaid-eligible individuals whose medical needs require an institutional level of care, the waiver program provides Medicaid funding to States to provide those individuals HCBS in lieu of institutional care.2 42 U.S.C. § 1396n(e) (2006); 42 C.F.R. § 441.300 (2010); see Olmstead v. L.C., 527 U.S. 581, 601, 119 S.Ct. 2176, 144 L.Ed.2d 540 (1999). The waiver program permits an eligible recipient who is mentally retarded to receive Medicaid-funded HCBS, rather than institutional care in an Intermediate Care Facility for the Mentally Retarded (ICF/MR). Once an individual is found eligible for such waiver services, a state must conduct periodic reviews to ensure the recipient still meets the waiver program eligibility requirements. 42 C.F.R. § 441.302(c)(2) (2010).
For purposes of basic Medicaid eligibility, the definition for mental retardation, in relevant part, is as follows:
Mental retardation refers to significantly subaverage general intellectual functioning -with deficits in adaptive functioning initially manifested during the developmental period; i.e., the evidence demonstrates or supports onset of impairment before age 22.
20 C.F.R. Pt. 404, Subpt. P, App. 1 § 12.05 (2011) (emphasis added).3
B.
For a state to participate in the Medicaid HCBS waiver program, it must submit a detailed application on a form provided by the federal government describing the group of individuals to whom the services will be offered. 42 C.F.R. § 441.301(b)(3) (2010). For the purpose of defining eligibility for waiver services, a state is free to impose in its waiver application eligibility criteria which are more restrictive than basic Medicaid eligibility requirements. 42 C.F.R. § 441.301(b)(6) (2010).
*66Based on South Carolina’s waiver application, to continue to be eligible to receive HCBS waiver services, a person must meet the following criteria:
1. The person has a confirmed diagnosis of mental retardation or a related disability.
AND
2. The person’s needs are such that supervision is necessary due to at least one of the following: impaired judgment, limited capabilities, behavior problems, abusiveness, assaultiveness or because of drug effects/medical monitorship.
AND
3. The person is in need of services directed toward a) the acquisition of the behaviors necessary to function -with as much self-determination and independence as possible; or b) the prevention or deceleration of regression or loss of current optimal functional status.
Attachment 1 to Appendix D-3, South Carolina’s Mental Retardation/Related Disabilities (MR/RD) Waiver Document (Effective October 1, 2004-September 30, 2009).
The second and third eligibility criteria are commonly referred to collectively as “Level of Care.” These criteria describe the minimum services and functional deficits necessary to qualify for Medicaid-sponsored institutional care in an ICF/MR. South Carolina’s waiver application provides that Level of Care reevaluations will take place at least every twelve months.4 Appendix D-2, South Carolina’s Mental Retardation/Related Disabilities (MR/RD) Waiver Document (Effective October 1, 2004-September 30, 2009). South Carolina’s waiver application with the federal government does not include any age-of-onset requirement and reveals no intent to vary from or otherwise limit the group of individuals encompassed by the SSI definition of mental retardation. On the waiver application in effect in 2005, South Carolina *67checked letter “f,” thereby expressing its intent to provide waiver services to the group identified as “mentally retarded persons and persons with related disabilities.” In addition, where asked whether it would impose any “additional] targeting restrictions” on the provision of waiver services, South Carolina stated “Not applicable.”
In 1990, the South Carolina General Assembly adopted a definition of mental retardation that parallels the SSI definition adopted by the federal government in 1985. See Act. No. 496, 1990 S.C. Acts 2184, 2187; 50 Fed.Reg. 35038, 35068-69 (Aug. 28, 1985). The definition, codified at South Carolina Code section 44-20-30, states that mental retardation is “significantly subaverage general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period.”5 The term “developmental period” was new to the 1990 definition, and it is upon the construction of that term that this matter largely turns.
DDSN promulgated a regulation which recites the SSI/44-20-30 definition of mental retardation (with only minor changes in phrasing) and defined the term “developmental period” as the period from conception to age twenty-two, consistent with the SSI definition.6 26 S.C.Code Ann. Regs. *6888-210(F) (Supp.2010). Thus the definition of mental retardation under state law — Regulation 88-210(F) — mirrors the SSI definition with respect to the age-of-onset requirement. No South Carolina regulation imposes additional diagnostic criteria for mental retardation in the context of waiver services. Nevertheless, DDSN attempted through a “Policy of Determination of Eligibility” to impose more restrictive diagnostic criteria for mental retardation for eligibility for waiver services in the form of an age-eighteen-onset requirement for mental retardation. The policy states:
DDSN evaluates referred individuals in accordance with the definitions of Mental Retardation outlined in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders-Foxxrih Edition (DSM-IV, 1994) and the American Association on Mental Retardation (AAMR 9th Edition, 1992).
Mental Retardation refers to substantial limitations in present functioning. Diagnosis of mental retardation based on the DSMPV and AAMR definitions requires the following three criteria be met:
3. The onset of mental retardation is before age 18 years. South Carolina Dep’t of Disabilities and Special Needs Policy for Determination of Eligibility Guidelines to Operationalize Eligibility Policy (Effective July 1, 1998) (emphasis added).7
*69II.
FACTUAL/PROCEDURAL HISTORY
Jane Doe was born on March 24, 1983, the product of an indisputably complicated birth. She was born at thirty weeks gestation, weighing just two pounds, three ounces. At ten months old, she was diagnosed with cerebral palsy, and her doctors diagnosed her with a seizure disorder at age eleven. As a result of her conditions, she has limited use of her left hand, difficulty with balance, and an awkward gait. Additionally, Doe presents with other physical and emotional conditions, including the nerve disorder Reflex Sympathetic Dystrophy, anxiety, depression, and anger management problems.
In 2001, Doe applied for SSI benefits from the SSA. The psychological evaluation submitted to the SSA showed her Full Scale Intelligence Quotient (IQ) to be sixty-nine, Verbal IQ to be seventy-seven, and Performance IQ to be sixty-five. Using these scores and personal observations of Doe’s functional abilities, the doctor examining her concluded “[s]he has multiple physical, mental, and emotional impairments, including cerebral palsy with left spastic hemiparesis and Mild Mental Retardation.” The SSA awarded Doe SSI based on a primary diagnosis of mental retardation and a secondary diagnosis of cerebral palsy. That determination has never been challenged.8 Respondent South Carolina Department of Health and Human Services (HHS) and its agent, DDSN, sought reimbursement from the federal government for ser*70vices they supplied using the diagnostic code for mental retardation.
Doe is unquestionably disabled. Looking to her IQ scores beginning at age twelve, Doe’s full-scale IQ scores ranged from a low of sixty-six to a high of seventy-three.
DDSN approved Doe’s application for waiver services in March 2003, and provided her with HCBS. Because Doe’s parents were unable to care for her at home, DDSN placed Doe in a Community Training Home II (CTH II) facility operated by the Newberry County Disabilities and Special Needs Board.9
In 2005, DDSN re-evaluated and terminated Doe’s eligibility for waiver services. Doe contended her benefits should not be terminated and requested a fair hearing to review that decision pursuant to 42 U.S.C. § 1396a(a)(3) (2006) and section 126-380 of the South Carolina Code of Regulations. Relying on DDSN’s definition of mental retardation in its policy guidelines that the onset of mental retardation must occur prior to age eighteen, the Hearing Officer referenced “accepted psychological doctrine” and concluded Doe was not mentally retarded.10 Finding the absence of mental retardation (and related disability) dispositive, the Hearing Officer did not reach the issue of whether Doe met the Level of Care requirements for waiver services eligibility. The ALC affirmed the Hearing Officer. This appeal followed.
III.
STANDARD OF REVIEW
Our standard of review is governed by the Administrative Procedures Act. S.C.Code Ann. § 1-23-380(5) (Supp.2010). *71The Court may affirm the agency’s decision, remand the matter, or reverse or modify it
if substantial* rights of the appellant have been prejudiced because the administrative findings, inferences, conclusions, or decisions are:
(a) in violation of constitutional or statutory provisions;
(b) in excess of the statutory authority granted of the agency;
(c) made upon unlawful procedure;
(d) affected by other error of law;
(e) clearly erroneous in view of the reliable, probative, and substantial evidence on the whole record; or
(f) arbitrary or capricious or characterized by abuse of discretion or clearly unwarranted exercise of discretion.
Id. We reverse because the decisions of the Hearing Officer and ALC are controlled by an error of law.
IY.
LAW/ANALYSIS
A.
It is Doe’s position that the SSA determination of disability and receipt of basic Medicaid through SSI is binding on DDSN’s determination of whether she is entitled to receive waiver services. In the alternative, Doe argues it was error to impose an age-eighteen-onset requirement in determining whether she is mentally retarded and that DDSN must use the age-twenty-two-onset definition of mental retardation.
We disagree that, in the context of waiver services, DDSN is bound by the SSA’s determination that Doe is disabled, for Doe conflates her entitlement to basic Medicaid services by virtue of her SSI disability with the issue of whether she is eligible to receive HCBS through the optional Medicaid waiver program. The federal government has made it manifestly clear that states have wide discretion in designing a waiver program that is tailored to the needs of the particular state. For example, in the “Application for a § 1915(c) Home and Community-Based Services Waiver” promulgated by the Cen*72ters for Medicare & Medicaid Services, the purpose of the HCBS Waiver Program is as follows:
The Medicaid Home and Community-Based Services (HCBS) waiver program is authorized in § 1915(c) of the Social Security Act. The program permits a State to furnish an array of home and community-based services that assist Medicaid beneficiaries to live in the community and avoid institutionalization. The State has broad discretion to design its waiver program to address the needs of the waiver’s target population. Waiver services complement and/or supplement the services that are available to participants through the Medicaid State plan and other federal, state and local public programs as well as the supports that families and communities provide.
The Centers for Medicare & Medicaid Services (CMS) recognize[] that the design and operational features of a waiver program will vary depending on the specific needs of the target population, the resources available to the State, service delivery system structure, State goals and objectives, and other factors. A State has the latitude to design a waiver program that is cost-effective and employs a variety of service delivery approaches, including participant direction of services.
Therefore, it is clear that states may impose additional criteria to the SSI definition of mental retardation for the purposes of waiver services eligibility, and the SSI’s prior determination of Doe as mentally retarded is not binding on the state’s waiver services eligibility determination of whether Doe is mentally retarded.
B.
Although we reject Doe’s initial argument, we do agree with her contention that it was error to impose an age-eighteen-onset requirement in determining whether she is mentally retarded. South Carolina’s waiver application allows it to do one very specific thing: substitute home or community based services (HCBS) for mandatory Medicaid services with respect to a defined subset of categorically needy persons, without providing HCBS to every categorically needy person in the State. 42 C.F.R. § 440.240(b) (2010) (“The [State] plan must provide that the services available to any individual in *73the following groups are equal in amount, duration, and scope for all recipients within the group: (1) The categorically needy ----”); id. § 440.250(k) (“[T]he services provided under [a] waiver [of § 440.240] need not be comparable for all individuals within a group.”); id. § 441.301(b)(6) (requiring a waiver request to “[b]e limited to one of the ... target groups or any subgroup thereof’ and defining the target groups as the aged, disabled, mentally retarded, developmentally disabled, and mentally ill). Thus, the scope of HCBS furnished under the waiver program and recipient eligibility criteria are defined by the waiver application. However, South Carolina’s waiver application with the federal government does not include any age-of-onset requirement.
To the extent a state is permitted to issue regulations interpreting the general eligibility requirements included in its waiver application, South Carolina regulations reveal no intent to vary from the requirement that the onset of mental retardation occur prior to age twenty-two. Rather, the only regulation addressing eligibility for HCBS states that HCBS “may be provided to Medicaid eligible persons eighteen years of age or older, who have been determined by community long term care to require a skilled or intermediate level of care.” 27 S.C.Code Ann. Regs. 126-304 (1976). No South Carolina regulation imposes additional diagnostic criteria for mental retardation in the context of waiver services.
Moreover, we find DDSN’s policy guidelines are not entitled to any deference in this regard. The scope of DDSN’s rulemaking authority is defined by the South Carolina General Assembly, and DDSN may exercise such authority only in that manner. As discussed above, in 1990, the General Assembly adopted a definition of mental retardation in line with the SSI definition adopted by the federal government in 1985. Thereafter, DDSN promulgated regulation 88-210(F), which recites the SSI/44-20-30 definition of mental retardation and defines the term “developmental period” as the period from conception to age twenty-two, consistent with the SSI definition.11 *74Thus, the informal agency policy issued by DDSN, purporting to implement an age-eighteen-onset requirement should be disregarded in determining what classes of mentally retarded South Carolinians are entitled to Medicaid waiver services because it lacks the force and effect of law and is in direct conflict with Regulation 88-210(F), which defines the developmental period as extending to age twenty-two.
Y.
CONCLUSION
In sum, it is clear that South Carolina could have listed additional criteria in the waiver application for the purpose of defining the population to whom it would provide waiver services. Likewise, DDSN could have promulgated regulations incorporating those additional criteria as part of the definition of mental retardation. But no such steps were taken. Rather, South Carolina adopted a broad definition of mental retardation in section 44-20-30, using language that parallels the SSI definition, and in Regulation 88-210, DDSN interpreted that definition in a manner consistent with the SSA. DDSN’s interpretation of section 44-20-30 in its policy guidelines directly conflicts with Regulation 88-210 and should be disregarded.
We find the Hearing Officer and ALC erred in applying an age-eighteen-onset requirement for mental retardation. We reverse and remand for consideration of whether, applying the proper legal standard for mental retardation (onset prior to age twenty-two), Doe is eligible to continue to receive waiver services.
*75REVERSED AND REMANDED.
TOAL, C.J. and BEATTY, J., concur. HEARN, J. concurring in part and dissenting in part in a separate opinion in which PLEICONES, J., concurs.. Final Administrative Order, June 5, 2006.
. A showing that the average annual cost of HCBS would not exceed that of institutional services is also required. 42 U.S.C. § 1396n(c)(2)(D) (2006).
. Although this particular part of the regulations concerns benefits under a different portion of the Social Security Act, this listing of impairments is the operative listing for Supplemental Security Income and Medicaid purposes. 20 C.F.R. § 416.905 (2011).
. South Carolina filed a Request for a Renewal to a § 1915(c) Home .and Community-Based Services Waiver (Effective January 1, 2010) and a Request for an Amendment to a § 1915(c) Home and Community-Based Waiver (Effective March 1, 2011). However, neither the renewal or amendment waiver application altered the Level of Care evaluation criteria or frequency.
. Prior to the 1990 Act, South Carolina defined a "mentally retarded person" as "any person, other than a mentally ill person primarily in need of mental health services, whose intellectual deficit and adaptive level of behavior require for his benefit, or that of the public, special training, education, supervision, treatment, care or control in his home or community, or in a service facility or program under the control and management of the Department.” S.C.Code Ann. § 44-21-30 (1976).
Subsequent to the briefing and arguments in this case, the General Assembly, in 2011 Act No. 47, changed the references to mental retardation in section 44-20-30 to "intellectual disability.” Although the definition of intellectual disability is the same as it was for mental retardation, it has been moved to subsection 12 of section 44-20-30. To ensure our references are consistent with the record in this case, we will continue to use the terminology in effect at the time this case arose and was argued.
. Chapter 88 of the South Carolina Code of Regulations draws its statutory authority from title 44, chapter 20 of the South Carolina Code. While chapter 88 continues to list its statutory authority as article 3 of chapter 21, title 44 of the 1976 Code, that article was repealed in 1990. The relevant statutory provisions were reenacted as article 5 of chapter 20. This change was part of the same act that adopted the new *68definition in section 44-20-30. 1990 S.C. Acts 2184, 2200-04. Notably, while the pre-1990 definition of mental retardation applied only to the article of title 44 in which it was located, the new definition in section 44-20-30 explicitly applied to the entire chapter. Thus, the General Assembly manifested its intent that the definition in section 44-20-30 would apply to the licensing provisions interpreted in chapter 88 of the South Carolina Code of Regulations. Those regulations dictate that the developmental period extends to age twenty-two. In the more than twenty years following these changes in the law, DDSN has not altered the regulations to reflect a contrary view.
. In ignoring Regulation 88-210 and finding DDSN's policy guidelines properly supplied more specific criteria outside the waiver application, the dissent acknowledges the fact that DDSN's policy guidelines are not regulations promulgated by a state agency; yet the dissent finds the policy guidelines are entitled to deference in interpreting section 44-20-30. In accordance with our statutory law, we hold an agency guideline does not have the force of law, and in any event, can never *69trump a regulation. Our law provides that " ‘[r]egulation' means each agency statement of general public applicability that implements or prescribes law or policy or practice requirements of any agency. Policy or guidance issued by an agency other than in a regulation does not have the force or effect of law." S.C.Code Ann. § 1-23-10(4) (2005) (emphasis added). Thus, because the age-eighteen-onset requirement found in DDSN’s policy guidelines has not been formally adopted as a regulation, it does not have the force and effect of law and is entitled to no deference. Indeed, the only South Carolina law addressing the age onset requirement is Regulation 88-210.
. In other litigation involving Doe, the United States Court of Appeals for the Fourth Circuit noted that Doe "has developmental disabilities including epilepsy, mild mental retardation, and cerebral palsy." Doe v. Kidd, 501 F.3d 348, 351 (4th Cir.2007).
. A CTH II is not an ICF/MR facility; it is classified as respite care rather than institutional care. Patients in a CTH II receive twenty-four hour supervision and some training depending on their assessed needs and care. A CTH II facility has one to two staff responsible for up to four individuals. During the pendency of this appeal, DDSN agreed to continue providing Doe HCBS benefits.
. The hearing officer further determined that Doe did not meet the definition of a related disability. Because we conclude the hearing officer applied the incorrect definition of mental retardation, we need not reach Doe’s separate challenge to the related disability finding.
. The dissent asserts that Regulation 88-210 is inapplicable to the question before us because it refers only to licensing, not eligibility. This ignores the fact that Regulation 88-210 is an interpretation of the same statute, section 44-20-30, purportedly interpreted by DDSN’s policy guidelines. We adhere to the basic principle that the same word *74should not be given disparate meanings within a single statutory scheme. Further, the plain language of the regulation shows that the definitions in 88-210 apply to the licensing of all programs "for the care, maintenance, education, training or treatment” of mentally retarded persons that operate for at least ten hours per week, unless specifically excluded. 26 S.C.Code Ann. Regs. 88-105. Nothing in the text of 88-105 or 88-210 excludes non-residential waiver services from the scope of the definitions found therein, and the dissent does not appear to contest that some of the programs subject to the definitions in 88-210 are waiver services. Therefore, in our view, Regulation 88-210 expresses the view that the term "developmental period” in section 44-20-30 has the same meaning in the context of waiver services as it does in the context of basic Medicaid services.