Opinion by
Judge RULAND.Defendant, Arapahoe County Board of Equalization (County), appeals from a judgment of the trial court reducing the valuation of plaintiffs’ residential properties for taxation purposes. We affirm.
In the 1993 reassessment year, the county assessor appraised the improvements on the residences owned by plaintiffs, Richard and Robert Podoll, at $503,306 and $474,880, respectively. These valuations were protested to the assessor and then the County. As a result of these appeals, some adjustments were made. However, plaintiffs requested further relief by complaint in the district court pursuant to § 39-8-108(1), C.R.S. (1994 Repl.Vol. 16B).
All of the residences in the subdivision where plaintiffs resided were primarily large brick and frame units on one acre lots, with comparable construction quality and amenities. In support of their claim of overvaluation, exhibits were admitted indicating assessed valuations for the 1991 and 1993 tax years and averaged values per square foot for plaintiffs’ residences as compared with over 20 similar residences in the same neighborhood. These exhibits reflect substantial disparity in the valuations on plaintiffs’ residences as compared to the others.
A 1992 order of the Board of Assessment Appeals (BAA) was also admitted. This order reduced the valuations of plaintiffs’ residences following the 1991 tax reassessment based upon evidence that the assessor’s valuation of plaintiffs’ residences exceeded $80 *863per square foot with a quality grade of “450” while comparable properties in the same subdivision were valued at only an average of $53 per square foot with quality grades of “400” and “425.” In its order, the BAA found that the County’s market valuation based upon comparable sales supported a higher valuation of plaintiffs’ residences, but that it viewed plaintiffs’ residence as overvalued under the foregoing circumstances.
Plaintiffs’ evidence further showed that, in the majority of properties in the subdivision, improvement valuations increased an average of 10.73% from 1991, while plaintiffs’ assessments increased by over 32%. This translated into an average assessment of over $63 per square foot for the comparables and approximately $85 per square foot for plaintiffs.
In support of the County’s valuation, an appraiser from the assessors’ office testified that she conducted an individual market approach appraisal of plaintiffs’ properties using confirmed sales of comparable properties in the area since the 1991 reassessment. She indicated that, during the pendency of this appeal, she attempted to review the interiors of the properties, but was denied access by plaintiffs. As a result, all the information used both in the initial assessment and her appraisal was based upon the improvements as originally constructed.
She further testified that equalization in valuations was achieved by using a median value for a particular neighborhood, adjusted for size, quality grade, and specific amenities. According to this witness, the Property Tax Administrator’s guidelines do not allow for an averaging of value per square foot as plaintiffs had done.
The trial court found no reasonable explanation for the disparity in the valuation of the plaintiffs’ residences compared to the “vast majority” of comparable properties in the subdivision. The trial court concluded that the assessor had improperly failed to equalize the value of plaintiffs’ residences with the others in the subdivision and ordered the valuations reduced to $381,365 and $386,240.
I
The County first contends that plaintiffs failed to meet their burden to show that the County’s valuations were incorrect because the per square foot calculations relied upon are not permissible indicators of market valuation for tax purposes. In effect, the County argues that plaintiffs are not entitled to a tax adjustment by establishing that their residences are taxed at a rate far in excess of similar homes in the same subdivision. Based upon the foregoing, the County concludes that the court was required to accept its evidence of market value based upon comparable sales in the area. We are not persuaded.
Section 39-1-104(10.2), C.R.S. (1994 Repl. Vol. 16B) directs the assessor to establish the “actual value” of taxable real property during each of two calendar years based upon the factors enumerated in § 39-1-103(5), C.R.S. (1994 RepLVol. 16B). This statute, in turn, requires that the actual value of residential property be determined based upon the market and cost approach to value.
A recent constitutional amendment, Colo. Const, art. X, § 20, also provides that:
Actual value shall be stated on all property tax bills and valuation notices and, for residential real property, determined solely by the market approach to appraisal.
However, both Colo. Const, art. X, § 3, and § 39-1-101, C.R.S. (1994 Repl.Vol. 16B) require that:
The actual value of all real and personal property ... shall be determined under general laws ... as shall secure just and equalized valuations for assessments....
See Boulder County Board of Equalization v. M.D.C. Construction Co., 830 P.2d 975 (Colo.1992)(legislative declaration under § 39-1-101 requires general property tax provisions to be strictly construed for the purpose of securing just and equalized valuations).
Further, the equality mandated under Colo. Const, art. X, § 3 requires that the same means and methods be applied impartially to all the members of each class, operating equally and uniformly upon all persons or property in similar circumstances. See *864District 50 Metropolitan Recreation District v. Burnside, 167 Colo. 425, 448 P.2d 788 (1968); Citizens’ Committee for Fair Property Taxation v. Warner, 127 Colo. 121, 254 P.2d 1005 (1953).
Given this state of the law, we must first address the issue whether plaintiffs were entitled to challenge the County’s assessment based upon evidence that the assessor had substantially over-valued their residences as compared to the others.
To the extent that the quoted constitutional provisions are arguably in conflict relative to the assessment of residential property, we must harmonize those provisions whenever possible. See Bolt v. Arapahoe County School District, 898 P.2d 525 (Colo.1995). That objective is accomplished here by interpreting the valuation concept contained in Colo. Const, art. X, § 20, to be subject, under appropriate circumstances, to the equalization requirement contained in Colo. Const, art. X, § 3. Under such an interpretation, a taxpayer would not be forced to forfeit a valid contention that the County abused its discretion by failing to equalize values.
Hence, here, the dispositive issue becomes whether the taxpayers have established a basis for reduction of their taxes because of the assessor’s failure to equalize property values in the subdivision. We conclude that they have.
The right to challenge taxes imposed based upon the failure of the assessor to equalize the assessment of comparable property has been implicitly recognized by divisions of this court in two recent eases consisting of Crocog Co. v. Arapahoe County Board of Equalization, 813 P.2d 768 (Colo.App.1990) and Bishop v. Board of Assessment Appeals, 899 P.2d 251 (Colo.App.1994). In each of those cases, the court found no abuse of discretion in the BAA’s decision not to award relief under the particular facts presented in each.
However, the division in Bishop in effect recognized that, under the equal protection analysis of the United States Supreme Court in Sioux City Bridge Co. v. Dakota County, 260 U.S. 441, 43 S.Ct. 190, 67 L.Ed. 340 (1923), the taxpayer would be entitled to an adjustment of real estate taxes assessed if it were shown that the assessor intentionally and systematically valued other similar properties at substantially less than full value. We view that rule to be applicable here.
Specifically, the trial court found with record support that adjustments of the taxes imposed had been ordered in 1992 by the BAA because of the disparity between the assessments against plaintiffs as compared to the other residences in the subdivision. Notwithstanding this determination by the BAA, the County could offer no reasonable explanation why there was a 32.8% increase in the assessed values of plaintiffs’ residences following entry of the BAA’s order but only a 10.73% average increase as to the vast majority of comparable residences. In our view, these findings are tantamount to a determination that the actions of the assessor were arbitrary, and we therefore conclude that the trial court did not abuse its discretion in ordering an adjustment. See Sioux City Bridge Co. v. Dakota County, supra.
II
The County also contends that plaintiffs’ evidence relative to per square foot values assigned to their residences was inaccurate because their residences had been assigned a quality grade of 450 by the assessor, while the other comparable properties had quality grades of only 400 or 425. We disagree.
The County’s appraiser testified that a “quality grade” adjustment is made to the median value of homes in a particular neighborhood, which is determined by an individual appraisal of a given home’s interior. Although she stated that otherwise comparable properties in plaintiffs’ subdivision had quality grades of 400 or 425, she was unable to explain why plaintiffs’ homes were assigned a quality grade of 450. There was undisputed testimony that no improvements had been made on either of plaintiffs’ residences since the 1991 valuations.
Under these circumstances, there is record support for the court’s finding that the quality grade of 450 assigned to their properties was arbitrarily or mistakenly imposed. As such, we may not overturn the *865trial court’s findings. Cherry Hills Country Club v. Board of County Commissioners, 832 P.2d 1105 (Colo.App.1992).
III
Next, the County contends that the square footage measurements used by plaintiffs to compute value per square foot figures in their exhibits were erroneous, resulting in substantially higher values per square foot than if the correct figures had been used. However, this issue was not raised in the trial court. We, therefore, do not address it for the first time on appeal. See Artes-Roy v. City of Aspen, 856 P.2d 823 (Colo.1993).
IV
The County further argues that, by applying a flat percentage increase to the 1991 assessment values to determine the equalized valuation that should be applied to plaintiffs’ residences, the court in effect presumed that all residences in a neighborhood increase or decrease in value at the same percentage. We find no merit in this contention.
As we read the trial court’s order, it considered all of the evidence presented as to valuations and found that the actual valuation on the majority of comparable properties in plaintiffs’ subdivision increased from the 1991 assessment at a rate of 10.73%. Accordingly, the trial court equalized plaintiffs’ 1993 reassessment by applying a 10.73% increase to their 1991 valuations as determined in the BAA’s 1992 order.
V
Plaintiffs request an award of costs and attorney fees pursuant to C.A.R. 38(d), contending that this appeal is frivolous. We are not persuaded.
An appeal is “frivolous” if the appellant can present no rational argument based on the evidence or the law in support of his claim or defense, or if the appeal was pursued for the sole purpose of harassment or delay. See Wood Bros. Homes, Inc. v. Howard, 862 P.2d 925 (Colo.1993). From our examination of the record, we conclude that such is not the ease here.
The judgment is affirmed.
ROTHENBERG, J., concurs. ROY, J., dissents.