When a court decides a legal question, it creates a precedent. Unless a higher court or new legislation reverses the decision, the court’s decision has the effect of law. Court opinions are written to explain the Court’s decision. Research tools have been developed to assist someone who is doing legal research to determine if a Court’s opinion has been reversed by a higher court or legislation. Westlaw’s system is called KeyCite. Lexis\Nexis and Nexis Uni have a similar tool called Shepard's. When completing a legal research project you must use either KeyCite or Shepard's to determine if the court opinions you are relying upon to answer a legal question have not been overruled, distinguished or limited in some manner.