tioned on his satisfactorily performing in a JTA position for two years. Glass denied having ever been told that the probationary period was for two years but instead understood that a waiting period of indefinite duration was being imposed on him. In any event, a probationary period, whether two years or open-ended, was not applied to any other degreed candidate for an engineering job. Glass declined the job.
At trial, Weigand testified that he imposed the probationary period because of Glass’s poor performance while at Eddystone. Glass attempted to pursue the extent of Weigand’s knowledge of the Eddystone events on cross-examination:
Q Now, you said that you were aware of his past performance problems, in the technical field. How did you know what kinds of problems you thought he had had? Sorry. That’s a terrible question. What, quote, performance problems, close quote, were you aware of?
A I was aware that he was not receiving satisfactory performance appraisals in his JTA job at Eddystone Station, and I was aware that he was not being promoted to TA which is the normal progression, and that was in my organization, down a couple levels.
Q Were you aware that he had had difficulty on the job at Eddystone of a personal nature in connection with the other employees?
MS. KAHN: Objection, Your honor. Again, we’re going back into history which was ruled irrelevant.
THE COURT: The objection’s sustained.
App. at 426. With PECO’s objection sustained, Glass was repeatedly unable to introduce any evidence concerning the racially hostile environment at Eddystone station, management’s failure to take corrective action when it learned of the harassment, or the connection between these incidents and his negative performance evaluation.
We find that the district court abused its discretion for the following reasons: First, in the federal courts, the scope of permissible cross-examination is set forth in Fed.R.Evid. 611(b): “Cross-examination should be limited to the subject matter of the direct examination and matters affecting the credibility of the witness.” See also United States v. Sullivan, 803 F.2d 87, 90 (3d Cir.1986). The district court erred by allowing PECO’s witnesses, Lange, Riley and Weigand, to testify about their knowledge of the events at Eddy-stone but then not allowing Glass to cross-examine those witnesses as to the basis or extent of their knowledge.
Second, we find that the Eddystone evidence is independently relevant to a key aspect of the case: whether one of the principal non-diseriminatory reasons asserted by PECO for its actions was in fact a pretext for age or race discrimination. In St. Mary’s Honor Center v. Hicks, the Supreme Court confirmed that, under the well-established burden-shifting formula of McDonnell Douglas Corp. v. Green, 411 U.S. 792, 93 S.Ct. 1817, 36 L.Ed.2d 668 (1973), and Texas Dept. of Community Affairs v. Burdine, 450 U.S. 248, 101 S.Ct. 1089, 67 L.Ed.2d 207 (1981), in a Title VII case alleging employment discrimination:
First, the plaintiff has the burden of proving by a preponderance of the evidence a prima facie case of discrimination. Second, if the plaintiff succeeds in proving the prima facie case, the burden shifts to the defendant to articulate some legitimate, non-discriminatory reason for the employee’s rejection. Third, should the defendant carry this burden, the plaintiff must then have an opportunity to prove by a preponderance of the evidence that the legitimate reasons offered by the defendant were not his true reasons, but were a pretext for discrimination.
Burdine, 450 U.S. at 252-53, 101 S.Ct. at 1093; see St. Mary’s Honor Center, — U.S. at-, 113 S.Ct. at 2749 (reaffirming “our repeated admonition that the Title VII plaintiff at all times bears the ‘ultimate burden of persuasion’” of intentional discrimination). This formula applies equally to claims of age discrimination in employment under ADEA. See Chipollini v. Spencer Gifts, Inc., 814 F.2d 893, 897 (3d Cir.1987) (in bane). Since Glass had introduced sufficient evidence to establish a prima facie case and PECO had asserted several nondiscriminatory reasons