But how do we prove that the defendant was responsible, and how do we decide how much money they owe in damages?

Leak vs. U.S. Rubber Co.

One of the cases we look to in order to answer these questions is Leak vs. United States Rubber Co. (511 P. 2d 88 – Wash: Court of Appeals, 2nd the plaintiff was driving his pick-up truck when a wheel fell off, causing an accident.

The plaintiff sued the tire manufacturer as well as the company that installed the tire, and won a $48,000 verdict at trial.

Specifically, the plaintiff claimed that the accident was caused by the defendants’ failure to safely install the tire, and that the accident caused him to experience ongoing medical issues, including seizures, which were a pre-existing condition but allegedly aggravated by the accident.

The defendant appealed the verdict to the Washington State Court of Appeals, arguing several issues, including:

  • The plaintiff had failed to prove that the accident aggravated his existing seizures
  • There was not sufficient evidence to prove permanent injury. In other words, the defendant contended that they should not be liable for ongoing and future medical issues related to the accident, as the jury held they were.

Both of these questions raise a more fundamental one that the court had to consider; what evidence do plaintiffs need to support a claim for damages in a personal injury case?

Proving Liability

According to the court, to win damages “the plaintiff must produce sufficient evidence to establish with reasonable certainty a causal relationship between the injury and the subsequent condition.”

So how does the jury know whether there is sufficient evidence under this standard?

The court clarified that there is sufficient evidence when the jury “may decide the issue without indulging in speculation and conjecture.”

In other words, to win damages in a personal injury suit, we have to show, without any speculation, that there is likely a causal relationship between the accident and the injuries.

So what kinds of evidence can we employ to prove this?

The court further clarifies that either “direct or circumstantial evidence” may be sufficient to prove a causal relationship.

So, if we have direct, irrefutable evidence that the accident caused specific, measurable injuries, we have enough evidence for a jury to assign liability to the defendant.

However, direct irrefutable evidence is rare.

Usually, we only have circumstantial evidence. However, that evidence can be very persuasive to a jury, especially if it includes witnesses who can testify to the details of the incident.

What is important about this case is that it says circumstantial evidence of a causal relationship between an accident and injuries can be sufficient evidence for a jury to award damages.

Future Damages

Furthermore, the ruling notes that circumstantial evidence can be sufficient for awarding future damages, or costs related to ongoing future medical care, even if there is no direct evidence from a doctor testifying to the exact amount.

This is an important point, because it is often difficult for expert witnesses or treating doctors to estimate future medical damages. Instead, we can provide circumstantial evidence to a jury, showing how much care has cost, and how much it is likely to cost in the future, and the jury can use that information to determine damages.


To sum up, to prove damages in a personal injury case, we have to prove with a reasonable degree of certainty that the defendant(s)’ actions caused our client’s injuries.

Circumstantial evidence is sometimes enough to demonstrate this causation, but the evidence has to be persuasive to a jury.

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