What is the test for determining whether a defendant should be on probation rather than on probation?

"Defendants are entitled to sentencing decisions made in the exercise of the `informed discretion' of the sentencing court. [Citations.]" (People v. Belmontes (1983) 34 Cal.3d 335, 348, fn. 8.) A diagnostic study under Penal Code section 1203.03 provides the trial court with information on which to base discretion. (See People v. Vargas (1975) 53 Cal.App.3d 516, 532-533.) Here, the trial court apparently misperceived the diagnostic report to have recommended against probation when, in fact, only the "institutional staff recommendation" made that recommendation, and the "psychological evaluation" and the "administrative team" were of the opinion that probation was appropriate.