Final answer:
Comparative negligence is the defense doctrine that is applied in this situation.
Step-by-step explanation:
The defense doctrine that is applied in this situation is Comparative negligence. Comparative negligence is a legal principle that assigns responsibility for an injury or harm based on the degree of fault of each party involved.
In this case, the jury found that both Dr. Smith and the patient were 50 percent responsible for the patient's health problem. Therefore, their respective degrees of fault are compared and the damages awarded are adjusted accordingly.