The "Cat's Paw" theory (derived from a fable entitled "The Monkey and the Cat") refers to a person influencing the actions or decisions of another to accomplish his or her own goals. In Staub v. Proctor Hospital, 560 F.3d 647 (7th Cir. 2009), Vincent Staub, an army reservist, filed a lawsuit against his employer alleging that it had terminated his employment in violation of the Uniformed Services Employment and Reemployment Rights Act, 38 U.S.C. § 4301 et seq.

Specifically, Staub alleged that two supervisors and a co-worker were resentful of his military service and influenced his employer's decision to terminate his employment. The employer denied that their alleged animus played any role in the decision. A jury returned a verdict for Staub and the employer appealed to the U.S. Court of Appeals for the Seventh Circuit, which reversed.

The Seventh Circuit explained that the Cat's Paw theory of liability applies where a non-decision maker exercises "singular influence" over the decision maker. The Court further explained that exercising such influence occurs, for example, when the non-decision maker supplies false information or fails to provide accurate relevant information to the decision maker. According to the Court, however, when a decision maker conducts his or her own investigation and analysis before taking the alleged adverse action against the plaintiff, he or she mitigates the influence of the non-decision maker and "the [Cat's Paw] theory is not in play." Absent application of this theory, the Court explained, evidence of the non-decision maker's animus is irrelevant and inadmissible.

In Staub, the Seventh Circuit observed that the decision maker conducted an investigation before discharging Staub. Therefore, it explained, the Cat's Paw theory did not apply. The Court concluded that, absent the Cat's Paw theory, there was insufficient evidence to support Staub's discrimination claim. The Court reversed the judgment in favor of Staub and remanded the case to the district court with instructions to enter judgment in favor of the employer.

The circuit courts take different approaches to the Cat's Paw theory. In addition to the Seventh Circuit, the Fourth Circuit also follows the "Functional Decision Maker Standard" applied in Staub.

The Sixth, Ninth, Tenth, and Eleventh Circuits follow the more employee-friendly approach referred to as the "Causation Standard." According to this approach, if the discriminatory animus of a nondecision maker leads to or causes the decision maker's action - even if the decision maker also obtained unbiased information from other sources - then an employer is liable for discrimination.

A third standard, which is most favorable for employees, is the "Influence Standard," followed by the First, Second, Third, Fifth, Eighth, and the District of Columbia Circuits. Under this standard, liability is imputed to the employer when an unlawfully biased nondecision maker influenced or "played a role" in the decision making process.

In Staub, the Supreme Court is expected to clarify application of the Cat's Paw theory.