“ Respondent does not dispute that it would be highly improper for the disability pension payments to be considered in mitigation of the damages suffered by petitioner. Thus it has been recognized that:
'The Railroad Retirement Act is substantially a Social Security Act for employees of common carriers. ”

“ Respondent argues that the evidence of the disability payments, although concededly inadmissible to offset or mitigate damages, is admissible as bearing on the extent and duration of the disability suffered by petitioner. ”

“ Page v. St. Louis S. Ry. Co., 5 Cir., 312 F.2d 84, 94. See also Gregory and Kalven, Cases and Materials on Torts (1959) , pp. 480 482; McCormick, Damages (1935) , p. 310, n. 2; Comment, 38 Mich.L.Rev. 1073.↑ Cf. McCormick, Evidence (1954) , c. 19 ”