In medical malpractice cases, there is a legal theory known as “loss of chance” that helps attorneys model the value of life lost due to a missed or improper diagnosis. The theory argues that when a patient is improperly diagnosed, they lose bodily function or have a reduced chance of survival. In other words, there is a loss of chance to improve or stabilize their condition.

This should be understood as a distinct cause of action, separate from negligence. In other words, once we have established that the treating physician or other healthcare professional failed to meet the accepted standard of care, we can claim damages separately for two distinct causes of action:

  1. Personal injury or loss of life due to negligence
  2. Loss of chance to improve either the likelihood or length of survival or to improve bodily function (such as neurological function).

Importantly – loss of chance is a theory of injury valuation, not a theory of damages causation.

It is best understood by reviewing the following cases:

  1. Herskovits v. Group Health Coop. of Puget Sound, 99 Wn.2d 609, 664 P.2d 474 (1983)
  2. Mohr v. Grantham, 172 Wn.2d 844, 262 P.3d 490 (2011)
  3. Estate of Dormaier v. Columbia Basin Anesthesia, 177 Wash. App. 828, 313 P.3d 431 (2013)
  4. Matsuyama v. Birnbaum, 452 Mass. 1, 27 (2008).

Traditional tort principles require a loss of chance of more than 50 percent before recovery is permissible.

However, in the medical malpractice context, the doctrine broadens tort liability by allowing recovery even when the chance of survival or the chance of a better outcome has diminished to less than 50 percent.

This was first seen in Herskovits, in which the court allowed a 14 percent loss of chance of survival to move forward to a jury trial in a wrongful death case.

In Herskovits, three approaches to loss of chance were discussed.

  1. Traditional tort all-or-none: Under this theory, we must prove that the healthcare physician’s actions more probably than not caused the injury, and the plaintiff suffered a loss of chance greater than 50 percent.
  2. Substantial factor: This theory, adopted in Herskovits, argues that the medical error must be a “substantial factor” in causing the injury to seek damages, even when the lost chance attributable to the negligence is less than 50 percent.
  3. Proportionality approach: This theory, adopted by the concurring opinion in Herskovits, argues that causation must be proven on a more probable than not basis. However, the lost chance determines the amount of damages, and is calculated as a percentage of total injury recoverable under traditional all-or-none principles.

In the Mohr case in 2011, the court moved away from the substantial factor approach, and adopted the proportionality approach for loss of chance in medical malpractice cases.

Under that approach, a jury must find the following facts to consider damages:

  1. “the full amount of damages allowable for the injury,” without any probabilistic offset;
  2. the probability of survival (or better outcome) before the negligent act;
  3. the probability of survival (or better outcome) after the negligent act;
  4. the difference in probabilities between steps 2 and 3; and
  5. the product of the difference in probabilities in 4 and the full amount of damages in 1. Matsuyama v. Birnbaum, 452 Mass. 1, 27 (2008).

The Mohr court also extended loss of chance to include cases where the plaintiff does not die, but rather permanently loses bodily function.

The most recent case on these issues came in 2013, when the Dormaier court clarified when traditional versus loss of chance principles should apply. A lost chance of greater than 50 percent satisfies traditional causation, and triggers application of traditional all-or-none recovery.

A lost chance of 50 percent or less, the court said, requires proof that the lost chance is caused by negligent conduct on a more-probable-than-not basis. Once causation is established, damages are calculated using the proportionality method.


The Herskovits case (illustrated below) involved a patient who suffered from lung cancer. The x-axis represents the percentage chance of surviving for 5 years. The y-axis represents time.

At point t0 below, Herskovits developed lung cancer. His health deteriorated (reflected by the blue line) until point t1, when he saw his doctor.

The cancer was improperly diagnosed, resulting in a continued reduction in the chance of survival. This continued until the patient’s death at t3.

However – if the cancer had been properly diagnosed earlier, Herskovits life would have likely been extended further. This is shown by the dotted blue line, ending at t4.

In other words, the failure to diagnose the cancer caused Herskovits to suffer a reduction in chance of survival quicker than if the cancer had been properly diagnosed.

So how do we calculate the loss of chance in this case?

The red triangle in the chart below represents the total value of Herskovits’ life, without any medical negligence.

The area under the curve below, from t1 to t3, shows the value of Herskovits’ life with the negligence.

Finally, the last chart below shows the loss of chance, reflected by subtracting the quality of life with the negligence from the total quality of life. This shape under the curve represents the loss of chance Herskovits suffered.

Mohr Case

The Mohr case is different from Herskovits primarily because the patient did not die. Instead, the patient suffered a loss of neurological function, beginning at t0. Doctors’ failure to properly treat Mohr when she first sought help at t1 caused her to suffer a continued decline of neurological function until t2. At that point, she was properly treated, continued to decline until t4, and then finally stabilized with substantially reduced neurological function.

In this case, we can also evaluate what Mohr lost by looking at the area under the curve. The chart below shows the total value of Mohr’s life by mapping an area between the initial treatment, the stabilization of neurological function, and the best case scenario for treatment.

However, Mohr was not treated properly at t1. The next chart below shows the value of life with the negligence.

Like in Herskovits, we can illustrate the loss of chance by subtracting this area from the total value of life. This results in an area under the curve between t1 and t5 that reflects the loss of chance to improve and stabilize neurological function.


Loss of chance is an important concept in medical malpractice litigation. It is an extremely valuable tool for us to recover damages, even when the total loss is less than 50 percent, which is ordinarily the burden of proof for proving causation.

Loss of chance should be understood not as a separate theory of damages, but as a separate cause of action and a theory of valuing damages.