City of Lincoln appeals from an order of the Court of Industrial Relations increasing wages of Lincoln firemen and ordering the city to refund amounts withheld under a pay lag system. We affirm in part and reverse in part.
Lincoln Fire Fighters Association, Local 644, brought this action in the Court of Industrial Relations pursuant to section 48-811, R. R. S. 1943, alleging that its employment contract with the city of Lincoln had expired on September 1, 1975, and that the parties had failed to negotiate a new contract. A pretrial conference narrowed the issues to wages, longevity, clothing allowance, insurance, fire equipment operator pay, and prevailing rights in the contract.
By an order entered on April 5, 1976, the Court of Industrial Relations increased minimum wages by 12.3 percent and maximum wages by 8.6 percent, with intermediate wages increased by an amount equal to the average of the two figures. The court further ordered the city to refund money that had been withheld from pay checks in connection with the establishment of a pay lag system. No order *176was made on any of the fringe benefits since the court determined insufficient evidence had been presented on those issues. We first discuss the pay lag portion of the order.
The city instituted the pay lag system for all city employees, effective September 1, 1975. Under this system the 2-week pay period begins on a Thursday. Pay checks are issued on the second Friday following the completion of the pay period. The net result is that the payroll department has 7 working days to prepare the pay checks. Rather than delaying pay checks for 7 work days, in order to convert to this new accounting system, the city withheld .7 of each city employee’s biweekly pay checks, spread over eight pay periods. This money was placed in a pay lag fund to be paid out upon termination of employment. The employee receives no interest on the money placed in the fund.
All city employees except the firefighters received a 10 percent pay increase, beginning September 1, 1975. Because the firefighters had not renegotiated their contract, they were still paid the rate stipulated in the old contract less .7 for the pay lag fund for the 8 weeks. Even though this money would eventually be paid, each firefighter experienced a wage reduction of an amount equal to .7 of a biweekly pay check for eight pay periods.
We agree with the Court of Industrial Relations. The establishment of the pay lag is a change in wages, and cannot be established unilaterally during the term of an operative contract. We affirm that portion of the order which directs the city to pay the amount of the pay lag which was withheld from wages accruing under the existing contract.
The issue in this case was not whether the city could initiate a new accounting system referred to as a pay lag. The firefighters concede this may be done. It is the operation of the pay lag to the contract then in existence to which they object. Insofar *177as the order of the Court of Industrial Relations may be construed to disapprove of the adoption of a pay lag system as to future contracts, it is reversed.
The Union presented evidence which compared the Lincoln, Grand Island, and Omaha fire departments with respect to both wages and fringe benefits. The city offered wage comparisons from four different groupings of eight cities. The court rejected the evidence offered by the Union as not being comparable. It concluded, however, that one of the comparisons presented by the city was appropriate for determining prevalent wages and working conditions.
The court selected the West North Central Array by city population for purposes of comparison. These cities, with the estimated 1975 population, are: Des Moines (194,000), Cedar Rapids (109,900), and Davenport (100,300), Iowa; Wichita (264,000), Topeka (126,580), and Kansas City (169,000), Kansas; St. Paul (291,000), Minnesota; and Springfield (128,000), Missouri. Lincoln’s population estimate is 158,500. The city’s expert testified these cities were chosen on the basis of geographical location and population. Four of the cities have a greater population than Lincoln, and four have a lesser population. In selecting this particular array of cities over the other three presented by the city, the court also considered similarity of working conditions, including such factors as the size of firefighting forces, population density, and climatic conditions.
The minimum rate of pay for Lincoln firefighters was shown to be 9 percent below the arithmetic mean of the minimum rate in the eight cities, as of September 1975. The maximum rate of pay was 5.3 percent below the arithmetic mean. The court ordered the wages for the Lincoln firefighters increased by these amounts.
The court also found that contracts in five of the *178eight cities had January 1 for a starting date, and that Cedar Rapids and Omaha (which was not one of the cities in the array) showed an increase of 5 percent for calendar year 1976. Based on this fact, the court determined that an average increase of 5 percent could be expected for 1976.
It then determined that because the contract involved commenced on September 1, 1975, only 8 months would be subject to this 5 percent increase. Thus, the court ordered an additional increase of two-thirds of 5 percent, or 3.3 percent. In effect, the minimum wage was ordered increased by 12.3 percent, and the maximum wage by 8.6 percent with intermediate wages increased by an average of these two figures.
The city maintains the court should not have ordered a wage increase after rejecting the evidence presented by the Union. This contention is without merit. It is true the burden is on the moving party in a section 48-818, R. R. S. 1943, case, to demonstrate that existing wages are not comparable to the prevalent wage rate, but all evidence contained in the record may be considered for this purpose. There is no merit to the city’s contention that the city’s evidence cannot be used. The burden of proof is satisfied by actual proof of the facts, of which proof is necessary, regardless of which party introduces the evidence. 31A C. J. S., Evidence, § 104, p. 176.
In Omaha Assn. of Firefighters v. City of Omaha, 194 Neb. 436, 231 N. W. 2d 710 (1975), we held that prevalent wage rates for firemen must of necessity be determined by comparison with wages paid for comparable services in reasonably similar labor markets. In section 48-818, R. R. S. 1943, in selecting cities in reasonably similar labor markets, for the purposes of comparison in arriving at comparable and prevalent wage rates, the question was whether as a matter of fact the cities selected for *179comparison are sufficiently similar and have enough like characteristics to make comparisons appropriate.
We conclude there was sufficient evidence for the court to find that wages received by Lincoln firefighters were not comparable to prevalent wage rates. In selecting the fire departments to be used for comparison, the court considered the size and complexity of the firefighting forces and the physical conditions under which the firefighters work is done. Among those factors considered were geographical proximity to Lincoln and similarities in population, population density, force size, and weather conditions. The method of selection employed was in accord with the requirements of section 48-818, R. R. S. 1943.
However, the method of comparison used by the court did not comply with the statutory requirements. The evidence in this case showed the eight cities selected for comparison had on the average more than twice as much manufacturing as Lincoln, and presumably more unionization. There was also evidence that the median income in the cities selected was generally higher than the median income in Lincoln. Because the evidence established the cities selected were economically dissimilar to Lincoln, it was error for the court to utilize directly the mean wage rate of those cities in determining the prevalent wage rate.
In Omaha Assn. of Firefighters v. City of Omaha, 194 Neb. 436, 231 N. W. 2d 710 (1975), we stated: “A prevalent wage rate to be determined by the Court of Industrial Relations must almost invariably be determined after consideration of a combination of factors. * * * It must be noted also that in this case the Court of Industrial Relations did not determine the prevalent wage rates for firemen by any direct computation or application of average or mean rates from seven cities nor from ten cities. Instead, it *180weighed, compared, and adjusted all the factors involved in each of the cities which resulted in a determination of prevalent wages paid for comparable services in reasonably similar labor markets.”
We hold that in determining prevalent wage rates for comparable services in reasonably similar labor markets, the Court of Industrial Relations is required to weigh, compare, and adjust for any economic dissimilarities shown to exist which have a bearing on prevalent wage rates.
In Omaha Assn. of Firefighters v. City of Omaha, supra, we further stated: ‘‘In establishing wage rates under section 48-818, R. R. S. 1943, the Court of Industrial Relations is required to take into consideration the overall compensation received by the employees, including all fringe benefits.” This was not done in this case as no evidence was presented on fringe benefits received by the firemen in those cities used for comparison.
The Court of Industrial Relations was further in error in adjusting wages upward by 3.3 percent to compensate for anticipated increases in 1976. The only evidence presented on this point was that contracts in five of the eight cities were subject to renewal in January 1976, and that in two cities, Cedar Rapids and Omaha, wages were to be increased by 5 percent. Omaha, however, was not one of the cities included in the comparison, and further, the court had specifically rejected it as not being comparable. It is evident this figure was arrived at by speculation, surmise, or conjecture. An issue depending entirely upon speculation, surmise, or conjecture is never sufficient to sustain a judgment, and one so based must be set aside. Mitchell v. Eyre, 190 Neb. 182, 206 N. W. 2d 839 (1973).
We affirm the judgment of the Court of Industrial Relations insofar as it directs the payment of the pay lag withheld from the wages of the firefighters. We reverse the judgment in all other particulars, *181and remand the cause to the Court of Industrial Relations with directions to make a determination of the prevalent rate of pay based upon a consideration of overall compensation received during the relevant period. We further direct that in its application to Lincoln, the court make an appropriate adjustment for economic variables as described heretofore.
Affirmed in part, and in part reversed AND REMANDED WITH DIRECTIONS.