Although Federal Rule of Evidence 409 or a comparable State rule bars evidence of paying for or furnishing medical, hospital, or similar expenses if such evidence is offered to prove liability, such evidence is not barred by Rule 409 or a comparable State rule if the evidence is offered to impeach a witness by showing bias or prejudice.

Josephs v. Pacific Bell, 432 F.3d 1006, 1017 (9th Cir. 2005) (holding, in plaintiff employee's action against defendant employer for discrimination, that evidence of statements made during employee's grievance proceeding....Although settlement negotiations and offers are inadmissible (i) to show the validity or invalidity of a claim when validity is in dispute, (ii) to show the amount of damages when the amount is in dispute, or (iii) to impeach by showing a prior inconsistent statement or specific contradiction, evidence about settlements and settlement offers and negotiations in civil actions is admissible for a wide variety of purposes; such settlement evidence is admissible whenever it is not offered on a disputed question of the validity of a claim or its amount or to impeach a witness with a prior inconsistent statement or by specific contradiction.

Cf. Barefoot v. Estelle, 463 U.S. 880, 899 (1983) (although finding that evidence of defendant's dangerousness was not barred by due process, there is a negative pregnant buried in the Court's conclusion: "We are not persuaded that that such testimony is almost entirely unreliable and that the...The Due Process guarantee of a fair trial may place some limits on the use of unreliable evidence in a criminal trial to show guilt.

Leonard v. Nationwide Mut. Ins. Co., 499 F.3d 419, 442 (5th Cir. 2007) (holding that the district court erroneously admitted statements made by insurer's agent to policyholders as "habit" evidence under Federal Rule of Evidence 406 because "evidence was lacking to suggest that [insurer agent's] statements...The routine practice of an organization is admissible under Federal Rule of Evidence 406 or a comparable State rule in order to show the conduct of the organization on a particular occasion, but a volitional routine practice cannot be used to show the conduct of a specific person on a particular occasion.