This case presents us with two questions. First, does R.C. 4123.57(B) require the Industrial Commission to aggregate all permanent partial disability awards, including those granted for injuries occurring prior to October 1, 1963, to determine when the one hundred percent permanent partial disability ceiling of R.C. 4123.57(B) has been reached? Second, is the statute unconstitutionally retroactive because it provides for aggregation of permanent partial compensation awards from injuries sustained before the 1963 amendment of R.C. 4123.57(B) with awards for injuries sustained after the 1963 amendment? We answer both questions in the affirmative. For the reasons that follow, we reverse the Court of Appeals for Franklin County, which issued a writ of mandamus ordering the commission to vacate its awards to Bednar for his 1982 and 1983 injuries, because “* * * when these awards are included with the other percentages of permanent disability awarded claimant, they exceed the one hundred percent limitation in violation of R.C. 4123.57(B).”
I
It is settled law that a relator has the burden of showing a clear legal right to a writ of mandamus as a remedy from a determination of the Industrial Commission. State, ex rel. Pressley, v. Indus. Comm. (1967), 11 Ohio St. 2d 141, 40 O.O. 2d 141, 228 N.E. 2d 631. See, also, State, ex rel. Westchester Estates, Inc., v. Bacon (1980), 61 Ohio St. 2d 42, 15 O.O. 3d 53, 399 N.E. 2d 81, paragraph one of the syllabus. It is also settled that mandamus will not lie where the record contains some evidence to support the commission’s findings. State, ex rel. Cassity, v. Montgomery Cty. Dept. of Sanitation (1990), 49 Ohio St. 3d 47, 48, 550 N.E. 2d 474, 475, citing State, *147ex rel. Burley, v. Coil Packing, Inc. (1987), 31 Ohio St. 3d 18, 31 OBR 70, 508 N.E. 2d 936; State, ex rel. Lewis, v. Diamond Foundry Co. (1987), 29 Ohio St. 3d 56, 57-58, 29 OBR 438, 440, 505 N.E. 2d 962, 964; State, ex rel. Paragon, v. Indus. Comm. (1983), 5 Ohio St. 3d 72, 74, 5 OBR 127, 128, 448 N.E. 2d 1372, 1374. Conversely, an abuse of discretion is present and mandamus will lie when there is no evidence upon which the commission could base its factual conclusions. Paragon, supra, at 74, 5 OBR at 128, 448 N.E. 2d at 1374, citing State, ex rel. Kramer, v. Indus. Comm. (1979), 59 Ohio St. 2d 39, 42, 13 O.O. 3d 30, 31, 391 N.E. 2d 1015, 1017.
R.C. 4123.57 (entitled “Partial disability compensation”) governs the schedule and number of weekly payments a claimant may receive for specified injuries arising out of and in the course of claimant’s employment. Effective October 1, 1963, the General Assembly amended paragraph (B) of this section by adding the following language:
“No award shall be made under this division based upon a percentage of disability which, when taken with all other percentages of permanent disability, exceeds one hundred per cent.” (Emphasis added.)
The first controversy of this case concerns the interpretation of this amendment. The commission, Bednar, and the amici curiae all urge this court to adopt the position that the amendment refers only to percentages of permanent disability resulting from injuries occurring after October 1, 1963, the amendment’s effective date. Under this interpretation, Bednar’s seventy-seven percent permanent partial compensation award received for the 1961 injury would not be aggregated with Bednar’s other permanent partial compensation percentage awards. Since Bednar’s awards would then total only fifty-eight percent,3 he would be eligible to receive the commission’s twelve percent and thirty percent permanent partial compensation awards for injuries occurring in 1982 and 1983, respectively.
Conversely, Sears urges this court to adopt the position that the amendment expressly refers to all prior awards, and thus that the seventy-seven percent permanent partial compensation award received for this 1961 injury must be included when calculating the aggregate total for permanent partial compensation percentage awards. Since Bednar’s percentage award would exceed one hundred percent when including the seventy-seven percent pre-1963 award, Bednar would be ineligible to receive the twelve percent and thirty percent awards for injuries occurring in 1982 and 1983, respectively. This is because Bednar would have already exceeded the statutory ceiling of one hundred percent4 before ever receiving his awards for the 1982 and 1983 injuries.
We believe the legislature ex*148pressed a clear and unambiguous intention in enacting this amendment to R.C. 4123.57(B) to have all permanent partial compensation percentage awards after 1963 aggregated in calculating the statutory one hundred percent ceiling mandated by this section.
The commission, Bednar, and the amici curiae would have this court insert the following italicized phrase, so that the amendment would read, in effect:
“* * * when taken with all other percentages of permanent disability resulting from injuries occurring after October 1, 1963 * * *.”
“[I]n determining the legislative intent of a statute ‘it is the duly of this court to give effect to the words used [in a statute], not to delete words used or to insert words not used. ’ (Emphasis added.)” Wheeling Steel Corp. v. Porterfield (1970), 24 Ohio St. 2d 24, 28, 53 O.O. 2d 13, 15, 263 N.E. 2d 249, 251, quoting Columbus-Suburban Coach Lines v. Pub. Util. Comm. (1969), 20 Ohio St. 2d 125, 127, 49 O.O. 2d 445, 446, 254 N.E. 2d 8, 9. The legislature had the perfect opportunity to include this language when it amended R.C. 4123.57(B), but chose not to do so. See id. Further, this court will not modify an unambiguous statute under the guise of judicial interpretation. Crowl v. DeLuca (1972), 29 Ohio St. 2d 53, 58 O.O. 2d 107, 278 N.E. 2d 352, citing Slingluff v. Weaver (1902), 66 Ohio St. 621, 64 N.E. 574, paragraph one of the syllabus.
II
Having found the 1963 amendment to R.C. 4123.57(B) to have a clear and unambiguous meaning, we must next answer the question of whether the amendment retroactively affects a claimant’s substantive rights. In re Nevius (1963), 174 Ohio St. 560, 23 O.O. 2d 239, 191 N.E. 2d 166. If R.C. 4123.57(B) does operate retroactively by aggregating awards for pre-1963 and post-1963 injuries, such aggregation is unconstitutional. Section 28, Article II, Ohio Constitution.
To answer the question, we must determine what it was Bednar lost in 1963. It is undisputed that his pre-1963 seventy-seven percent permanent partial compensation award remained undisturbed. State, ex rel. Frank, v. Keller, supra, at paragraph two of the syllabus. As of 1963, the seveniy-seven percent award was the only one in which he had a vested right when R.C. 4123.57(B) was amended. Sears asserts that this right is the only vested substantive right at issue in this case, and that because the 1963 amendment to R.C. 4123.57(B) did not affect that right, the amendment was not applied retrospectively.
We believe, however, that this analysis ignores another right that Bednar lost when R.C. 4123.57(B) was amended. The nature of this other right becomes apparent if permanent partial compensation claims are analyzed in terms of damage remedies. In State, ex rel. Latino, v. Indus. Comm. (1968), 13 Ohio St. 2d 103, 107-108, 42 O.O. 2d 324, 326, 234 N.E. 2d 912, 915, we recognized that the calculation of percentages of permanent disability in R.C. 4123.57(B) was used as a means of fixing “damage” awards, “* * * and not as an absolute limit to accumulated awards.” In other words, it is possible for a worker to be more than one hundred percent disabled. We adopted an *149analysis of such awards as damages rather than merely compensation for impairment of earning capacity. Id. at 108, 42 O.O. 2d at 326, 234 N.E. 2d at 915. Each permanent partial compensation claim is a discrete entity arising from a separate injury, in the same way that tort claims are considered individually, without regard to whether a claimant has prosecuted previous suits.
Workers’ compensation was instituted to deal with workers’ claims against their employers administratively, providing a tribunal to hear claims that would otherwise have been resolved by the courts. Section 35, Article II, Ohio Constitution; State, ex rel. Engle, v. Indus. Comm. (1944), 142 Ohio St. 425, 27 O.O. 370, 52 N.E. 2d 743. Workers’ compensation provides an alternative to the tort system, but it does not extinguish workers’ rights to a remedy for injuries on the job.
Section 35, Article II, Ohio Constitution begins by announcing its “* * * purpose of providing compensation to workmen and their dependents, for death, injuries or occupational disease, occasioned in the course of such workmen’s employment * * (Emphasis added.) Aggregating Bednar’s seventy-seven percent pre-1963 permanent partial compensation award with post-1963 awards would mean that Bednar could have been precluded from any remedy for a post-1963 injury that exceeded the remaining twenty-three percent of permanent partial compensation available to him. This could have left him with the 1982 and 1983 injuries for which he had no remedy under R.C. 4123.57(B). He therefore would have lost the right to press a claim for those injuries that was guaranteed by the Ohio Constitution.
The constitutional guarantee of compensation for such injuries is a substantive right. Because R.C. 4123.57(B) affected that right when the seventy-seven percent permanent partial compensation award was aggregated with post-1963 disability percentages, the statute operated to use prior awards to deprive Bednar of a substantive right. This constitutes a retroactive impairment of remedy for an injury in violation of Section 28, Article II, Ohio Constitution. It is retroactive because workers who had suffered injuries prior to the 1963 amendment were not afforded the equal opportunity to recover compensation for injuries as were those workers who had not sustained a compensable injury prior to the 1963 amendment. In other words, the statutory scheme attaches a consequence to pre-1963 awards which was not present when those awards were made.
However, we reject the notion that the General Assembly may not preclude permanent partial compensation percentages from aggregating more than one hundred percent on a prospective basis.5 In its prospective application to claims arising from injuries sustained after October 1, 1963, the *150provision in former R.C. 4123.57(B) (now in [A]) mandating a one hundred percent ceiling on awards for permanent partial compensation under workers’ compensation is constitutional. Retrospective application of the provision in R.C. 4123.57(B) (now in [A]) mandating a one hundred percent ceiling on awards for permanent partial compensation so as to aggregate awards for injuries sustained before October 1, 1963 with awards for injuries sustained after October 1, 1963 is unconstitutional. The policy arguments advanced against application of the 1963 legislation to post-1963 injuries do not rise to the level of constitutional right. Those arguments, if meritorious, must be addressed to the legislature.
Ill
In light of the unconstitutionality of aggregating pre-1963 permanent partial compensation award percentages with post-1963 award percentages, we conclude that the commission had some evidence before it upon which to base its factual conclusion that Bednar was entitled to receive the twelve percent and thirty percent awards for his 1982 and 1983 injuries, respectively. See State, ex rel. Burley, v. Coil Packing, Inc. (1987), 31 Ohio St. 3d 18, 31 OBR 70, 508 N.E. 2d 936, syllabus; State, ex rel. Rouch, v. Eagle Tool & Machine Co. (1986), 26 Ohio St. 3d 197, 198, 26 OBR 289, 290, 498 N.E. 2d 464, 466, fn. 1. The commission did not abuse its discretion in allowing these awards. Therefore, the court of appeals’ issuance of a writ of mandamus was inappropriate and is hereby reversed. The 1982 and 1983 awards of the Industrial Commission are reinstated.
Judgment reversed.
Moyer, C.J., H. Brown and Resnick, JJ., concur. Sweeney and Douglas, JJ., concur in part and dissent in part. Holmes, J., dissents.If the award for the 1961 injury is excluded, Bednar’s total permanent partial compensation percentage awards for injuries occurring in 1966 and 1981 would be fifty-eight percent (forty-eight percent and ten percent, respectively). If Bednar were allowed to receive his awards for the 1982 and 1983 injuries, his total under this interpretation would then be one hundred percent, meeting but not exceeding the statutory ceiling found in R.C. 4123.57(B).
If the award for the 1961 injury is included, Bednar’s total permanent partial compensation percentage awards for pre-1982 injuries would already exceed the one hundred percent statutory ceiling. In fact these awards would total one hundred *148thirty-five percent (a seventy-seven percent permanent partial compensation for the 1961 injury, a forty-eight percent permanent partial compensation for the 1966 injury, and a ten percent permanent partial compensation for the 1981 injury).
It has been suggested that the issue of the constitutionality of prospective application of the provision in former R.C. 4123.57(B) mandating a one hundred percent ceiling on awards for permanent partial compensation under workers’ compensation is not before us. The Industrial Commission raised this issue, however, on page three of the brief it submitted to us: “This case offers this court the opportunity to examine the extent of constitutional protection pursuant to the amendment under R.C. 4123.57(B).” The Attorney General then went on at length in support of our conclusion herein.