Standard of care
The standard of care is a legal concept used in the tort of negligence. To make out the tort one must establish: (1) that a duty of care owed by the defendant to the plaintiff; (2) the relevant standard of care relating to that duty; (3) that there has been a breach of the duty by the defendant; and (4) that the plaintiff has suffered damage as a result of the breach.
An example of the standard of care might be the level of treatment that a physician employs in treating a patient. If the care provided by the physician falls below the standard determined by the court and the patient suffers injury as a result, then the patient can sue for negligence. In Vaughn v. Menlove [1] the standard of care is defined as whether the individual "proceed[ed] with such reasonable caution as a prudent man would have exercised under such circumstances".
For professionals such as physicians, the standard of care is what a reasonably prudent professional would do under the circumstances. This "Bolam Test"[2] is used in medical malpractice cases.
More generally, courts often ask whether the additional precautions the defendant might have taken would have reduced the risk or amount of injury enough so as to be worth the defendant's effort. In other words, is the burden of taking a precaution less than the probability that precaution will avoid the harm multiplied by the size of that harm. If yes, then the defendant has not lived up to his standard of care and should be found negligent. This principle was first expressed by Judge Learned Hand in United States v. Carroll Towing.[3]