What is the standard of review analysis in the context of statutory review and judicial deference?

Dunsmuir has anchored many decisions on standard of review and judicial deference. In Dunsmuir the Court, however, said: 28 By virtue of the rule of law principle, all exercises of public authority must find their source in law. All decision-making powers have legal limits, derived from the enabling statute itself, the common or civil law or the Constitution. Judicial review is the means by which the courts supervise those who exercise statutory powers, to ensure that they do not overstep their legal authority. The function of judicial review is therefore to ensure the legality, the reasonableness and the fairness of the administrative process and its outcomes. 29 Administrative powers are exercised by decision makers according to statutory regimes that are themselves confined. A decision maker may not exercise authority not specifically assigned to him or her. By acting in the absence of legal authority, the decision maker transgresses the principle of the rule of law. Thus, when a reviewing court considers the scope of a decision-making power or the jurisdiction conferred by a statute, the standard of review analysis strives to determine what authority was intended to be given to the body in relation to the subject matter. This is done within the context of the courts' constitutional duty to ensure that public authorities do not overreach their lawful powers: Crevier v. Attorney General of Quebec, 1981 CanLII 30 (SCC), [1981] 2 S.C.R. 220, at p. 234; also Dr. Q v. College of Physicians and Surgeons of British Columbia, [2003] 1 S.C.R. 226, 2003 SCC 19, at para. 21.