Any employee making a claim of age discrimination ultimately bears the burden of proving that the challenged adverse employment action was based on the employee's age. Because direct evidence of such discriminatory motivation is rarely available, the courts have established a system of shifting burdens in an attempt to aid the presentation and resolution of employment discrimination claims that rely on circumstantial evidence to prove discriminatory intent. McDonnell Douglas Corp. v. Green (1973) 411 U.S. 792, 802-805 [93 S. Ct. 1817, 1824-1826, 36 L. Ed. 2d 668]; Hersant v. Department of Social Services (1997) 57 Cal. App. 4th 997, 1001-1005 [67 Cal. Rptr. 2d 483]; Caldwell v. Paramount Unified School Dist. (1995) 41 Cal. App. 4th 189, 195-205 [48 Cal. Rptr. 2d 448]; Martin v. Lockheed Missiles & Space Co. (1994) 29 Cal. App. 4th 1718, 1730-1731 [35 Cal. Rptr. 2d 181] This burden-shifting system requires the employee first to establish a prima facie case of age discrimination. In order to do so, the employee must offer circumstantial evidence giving rise to a reasonable inference of discrimination on the basis of age. The requirement is not an onerous one. (Hersant v. Department of Social Services, supra, 57 Cal. App. 4th at pp. 1002-1003; Heard v. Lockheed Missiles & Space Co. (1996) 44 Cal. App. 4th 1735, 1751 [52 Cal. Rptr. 2d 620].) In the context of the usual age discrimination case, a prima facie case of age discrimination arises when the employee shows that: (1) at the time of the adverse employment action, the employee was 40 years of age or older; (2) some adverse employment action was taken against the employee; (3) at the time of the adverse action the employee was satisfactorily performing his or her job; (4) the employee was replaced in his or her position by a significantly younger person. (Hersant v. Department of Social Services, supra, 57 Cal. App. 4th at p. 1003; Caldwell v. Paramount Unified School Dist., supra, 41 Cal. App. 4th at pp. 199-200; Mixon v. Fair Employment & Housing Com., supra, 192 Cal. App. 3d at p. 1318.) If the employee succeeds in establishing a prima facie case of age discrimination, the employer is then required to offer a legitimate, nondiscriminatory reason for the adverse employment action. If the employer fails to do so, the employee prevails. On the other hand, if the employer does articulate a presumptively valid, nondiscriminatory reason for its action, the burden then shifts back to the employee to demonstrate by competent evidence that the employer's stated reason for the adverse employment decision was in fact a pretext or coverup for age discrimination. This ultimate issue is decided on all the evidence. (McDonnell Douglas Corp. v. Green, supra, 411 U.S. at pp. 802-805 [93 S. Ct. at pp. 1824-1826]; Hersant v. Department of Social Services, supra, 57 Cal. App. 4th at pp. 1002-1003; Caldwell v. Paramount Unified School Dist., supra, 41 Cal. App. 4th at pp. 195-205; Martin v. Lockheed Missiles & Space Co., supra, 29 Cal. App. 4th at pp. 1730-1731, 35 Cal. Rptr. 181.) Even if the employee succeeds in establishing a prima facie case, however, the burden of persuasion never shifts to the employer. At all times, the burden of persuasion remains firmly on the employee to establish that the employer intentionally discriminated against the employee. Although the employer bears the burden of producing additional evidence of legitimate nondiscriminatory reasons, it need not persuade the court that it was actually motivated by the proffered reasons. It is only required to raise a genuine issue of fact as to whether it discriminated against the employee, by setting forth admissible evidence of its reasons for taking employment action adverse to the employee. (Caldwell v. Paramount Unified School Dist., supra, 41 Cal. App. 4th at pp. 200-201; Clark v. Claremont University Center (1992) 6 Cal. App. 4th 639, 663-664 [8 Cal. Rptr. 2d 151].) "In other words, once the employer produces evidence of a nondiscriminatory reason for its employment decision which, if believed by the fact finder, will support a verdict in the employer's favor, '. . . the factfinder must decide upon all of the evidence before it whether defendant intentionally discriminated against plaintiff. In short, the trier of fact decides whether it believes the employer's explanation of its actions or the employee's.' [Citation.]" ( Caldwell v. Paramount Unified School Dist., supra, 41 Cal. App. 4th at p. 201.) That is to say, once the employer has succeeded in carrying its burden of production, the entire framework for shifting presumptions and burdens between the parties " 'drops from the case' " and is no longer relevant. (Ibid.; see also St. Mary's Honor Center v. Hicks (1993) 509 U.S. 502, 509-511 [113 S. Ct. 2742, 2748-2750, 125 L. Ed. 2d 407] Mixon v. Fair Employment & Housing Com., supra, 192 Cal. App. 3d at p. 1319.) The employer's presentation of evidence of a legitimate nondiscriminatory reason for the adverse action having been made, the trier of fact proceeds to decide the ultimate question: whether the employee has proven that the employer intentionally discriminated against the employee. (St. Mary's Honor Center v. Hicks, supra, 509 U.S. at pp. 509-511 [113 S. Ct. at pp. 2748-2750]; Caldwell v. Paramount Unified School Dist., supra, 41 Cal. App. 4th at pp. 201-202.)