When ASI produced evidence of a legitimate, nondiscriminatory business reason for its conduct, it became Acrey's obligation to prove that ASI’s proffered justification was “a mere pretext for discrimination.” Connecticut v. Teal, 457 U.S. 440, 447, 102 S.Ct. 2525, 2530, 73 L.Ed.2d 130 (1982). A pretext can be established “by showing that the employer’s proffered explanation is unworthy of credence.” Mitchell v. Mobil Oil Corp., 896 F.2d 463, 471 (10th Cir.), cert. denied, — U.S. —, 111 S.Ct. 252, 112 L.Ed.2d 210 (1990); Krause v. Dresser Industries, Inc., 910 F.2d 674, 677 (10th Cir.1990); EEOC v. University of Oklahoma, 774 F.2d 999, 1002 (10th Cir.1985), cert. denied, 475 U.S. 1120, 106 S.Ct. 1637, 90 L.Ed.2d 183 (1986). In Merrick v. Northern Natural Gas Co., 911 F.2d 426, 430 (10th Cir.1990), we observed that after the employer presented evidence of a legitimate, non-discriminatory reason for Merrick’s termination, Merrick failed to introduce evidence giving rise to a genuine issue of material fact showing that the employer’s reasons were pretextual. The same vacuum exists in the instant case.
ASI’s evidence that Acrey’s post-merger work performance was unsatisfactory was not rebutted. To be sure, Acrey testified and presented the testimony of other witnesses that she had performed her work satisfactorily prior to the merger. Following the merger, however, the situation changed dramatically. The testimony of certified public accountants Dollinger, Smith and Zulauf, combined with that of White and Wasson, was uncontroverted on the point that Acrey was not able to perform her accounting work following the merger because the system was too complex for her. Acrey testified that after the merger she was not permitted to attend meetings with the accountants about setting up the new system (Appellee’s Supplemental Appendix to Answer Brief, Tab 5, p. 96) and she had not been given any training on the new Solomon system. Id. at 98. Mr. Paul Zulauf, senior auditor, testified that prior to putting the new accounting system into effect on July 1, 1989, he met with Acrey two or three times a week concerning the project [id., p. 39), and he, Dollinger, and Smith concluded that because Acrey’s experience had been in bookkeeping rather than accounting, she would not be able to manage the new accounting system. Id. at 46.
In EEOC v. Sperry Corp., 852 F.2d 503, 507 (10th Cir.1988), we held that an ADEA plaintiff must establish that age was a “determining factor” in the employer’s challenged, action. See also Lewis v. City of Ft. Collins, 903 F.2d 752, 755 n. 1 (10th Cir.1990). We explained in E.E.O.C. v. Prudential Fed. Sav. & Loan Ass’n. and Cooper v. Asplundh Tree Expert Co. that while a plaintiff need not prove that age was the sole reason for the employer’s acts, the plaintiff must show that age “made a difference” in the employer’s decision. 763 F.2d at 1170, 836 F.2d at 1547. In Cooper, we held that while a basic finding of liability under the ADEA requires only that age be at least one of the “determinative factors” in the employer’s conduct, in order to establish a willful violation, it is necessary to prove that age discrimination was the “predominant factor” in the employer’s decision. 836 F.2d at 1551.
There is no evidence in the record demonstrating that, given the complexity of the new accounting system and the efforts made to improve her performance, ASI discriminated against Acrey on account of her age. On the other hand, there is overwhelming evidence that Acrey’s job performance was not satisfactory following the implementation of the new accounting system. I conclude that, under these circumstances, Acrey’s ADEA claim must fail as a matter of law. There is a lack of evidence in the record to support the jury’s verdict. Colorado Coal Furnace Distribs. v. Prill Mfg. Co., 605 F.2d 499, 502 (10th Cir.1979). In Fallis v. Kerr-McGee Corp., 944 F.2d 743, 747 (10th Cir.1991), this court pertinently observed:
Under the law of this circuit, even if the jury chose to believe plaintiff’s assessment of his performance rather than Kerr-McGee’s, that choice, standing alone, does not permit a conclusion that