WPI 15.02 Proximate Cause—Substantial Factor Test

Use this instruction instead of WPI 15.01 (Proximate Cause—Definition) or WPI 15.01.01 (Proximate Cause—Definition—Alternative) in the narrow class of cases (discussed in the Comment below) for which the “but for” test of causation is inapplicable.

Section 431 of Restatement (Second) of Torts (1965) sets forth the “substantial factor” test of proximate cause, under which a defendant's conduct is a proximate cause of harm to another if that conduct is a substantial factor in bringing about the harm. In Blasick v. City of Yakima, 45 Wn.2d 309, 314–15, 274 P.2d 122 (1954), the Washington Supreme Court rejected this approach for general negligence actions in favor of the “but for” definition contained in WPI 15.01 (Proximate Cause—Definition). However, in Daugert v. Pappas, 104 Wn.2d 254, 262, 704 P.2d 600 (1985), while the court declined to apply the “substantial factor test” to a legal malpractice case, it indicated that the test may be appropriate in three types of cases:

Daugert v. Pappas, 104 Wn.2d at 262.

The substantial factor test has been adopted by Washington courts in a variety of cases involving discrimination or unfair employment practices. See Robel v. Roundup Corp., 148 Wn.2d 35, 46, 59 P.3d 611 (2002) (disability discrimination); Fell v. Spokane Transit Authority, 128 Wn.2d 618, 640, 911 P.2d 1319 (1996) (handicap discrimination in public accommodations); Mackay v. Acorn Custom Cabinetry, Inc., 127 Wn.2d 302, 310, 898 P.2d 284 (1995) (gender discrimination); Allison v. Housing Authority of City of Seattle, 118 Wn.2d 79, 93–95,821 P.2d 34 (1991) (age discrimination); Wilmot v. Kaiser Aluminum and Chemical Corp., 118 Wn.2d 46, 71, 821 P.2d 18 (1991) (retaliation for filing workers' compensation claim); Donahue v. Central WashingtonUniversity, 140 Wn.App. 17, 27–28, 163 P.3d 801 (2007) (retaliation for constitutionally protected speech); and City of Federal Way v. Public Employment Relations Com'n, 93 Wn.App. 509, 513–14, 970 P.2d 752 (1998) (retaliation for union organizing activity). For related pattern jury instructions using the substantial factor test, see WPI 330.01 (Employment Discrimination—Disparate Treatment—Burden of Proof), WPI 330.05 (Employment Discrimination—Retaliation), and WPI 330.31 (Disability Discrimination—Definition of Disability—Disparate Treatment Cases).

The Washington Supreme Court has also adopted the substantial factor test to determine the status of “seller” under the Securities Act of Washington. Haberman v. WPPSS, 109 Wn.2d 107, 130, 744 P.2d 1032 (1987). The court retained the test for such cases even after federal courts abandoned a similar prior interpretation of federal securities law. See Hines v. Data Line Systems, Inc., 114 Wn.2d 127, 148, 787 P.2d 8 (1990) and Hoffer v. State, 113 Wn.2d 148, 152, 776 P.2d 963 (1989).

In Mavroudis v. Pittsburgh-Corning Corp., 86 Wn.App. 22, 32, 935 P.2d 684 (1997), the Court of Appeals concluded that the substantial factor test should be used in multi-supplier asbestos-injury cases when expert testimony establishes that “all of the plaintiff's exposure probably played a role in causing the injury and that it was not possible to determine which exposures were, in fact, the cause of the condition.” The Mavroudis court reasoned that “[t]his is exactly the kind of situation that calls for application of the substantial factor test, in order that no supplier enjoy a causation defense solely on the ground that the plaintiff probably would have suffered the same disease from inhaling fibers originating from the products of other suppliers.” Mavroudis v. Pittsburgh-Corning Corp., 86 Wn.App. at 32.

The instruction used by the trial court in Mavroudis included a definition of “substantial factor”:

Mavroudis v. Pittsburgh-Corning Corp., 86 Wn.App. at 28. The Court of Appeals in Mavroudis did not expressly approve the wording of this instruction. Rather, the court held that any error that might exist in the instruction was not prejudicial. The court noted that the instruction may be unclear with regard to an insubstantial cause that combines with other causes to produce an injury, and the court further questioned whether the instruction went further than the Supreme Court would require in an asbestos-injury case. Mavroudis v. Pittsburgh-Corning Corp., 86 Wn.App. at 30–31.

In another toxic tort case, Hue v. Farmboy Spray Co., Inc., 127 Wn.2d 67, 87–88, 896 P.2d 682 (1995), the Supreme Court approved application of the substantial factor test to a claim for damages from the drift of a chemical cloud when the claim was brought against the manufacturer, the applicator, and numerous upwind wheat growers who had used the chemical at various times. The court required the plaintiff to prove that an individual defendant used the pesticide, that it became part of the drifting cloud, and that the cloud caused damage to the plaintiff.

Generally, the proper causation test in medical negligence actions for a loss of chance is the traditional “but for” test and not the substantial factor test. Dunnington v. Virginia Mason Med. Ctr., 187 Wn.2d 629, 389 P.3d 498 (2016); Rash v. Providence Health & Servs., 183 Wn.App. 612, 635–36, 334 P.3d 1154 (2014), review denied 182 Wn.2d 1028 (2015).

The Court of Appeals declined to extend the substantial factor test to a negligence or strict liability case involving a contaminated food product in Fabrique v. Choice Hotels Intern., Inc., 144 Wn.App. 675, 685, 183 P.3d 1118, 1122 (2008).