What is the "pragmatic and functional approach" used to determine the deference applicable to an administrative tribunal on an application for judicial review?

The pragmatic and functional approach is used to determine the appropriate degree of deference applicable to an administrative tribunal on an application for judicial review: Pushpanathan v. Canada (Minister of Employment and Immigration), 1998 CanLII 778 (SCC), [1998] 1 S.C.R. 982. The focus of the inquiry is on the particular provision at issue, the central analysis being whether the question raised is one that was intended by the legislators to be left to the exclusive determination of the administrative tribunal. The four factors are: (a) the presence or absence of a privative clause; (b) the relative expertise of the tribunal compared to that of the courts in deciding such a matter; (c) the purpose of the statute and the provision in particular; and (d) the nature of the problem.