(concurring and dissenting):
I concur with the result of the majority opinion. I dissent, however, from the holding that trial courts should not determine changed circumstances before applying the best interest test in all custody cases. I think that the threshold determination is valuable and necessary for all the reasons delineated in Hogge v. Hogge, 649 P.2d 51 (Utah 1982), and ought not to be abandoned. The rigidity which the majority fears has never been a necessary part of the test’s application, in my view, for the following reasons:
1. A change in the custodial relationship is a “change of circumstances” for purposes of reexamining custody. Thus, a deterioration of the child’s care or the capacity of the caretaker, for whatever reason (including the addition of other children or persons in the caretaker’s household), would be a proper subject of proof. It is true that in some cases, the evidence showing a change in the custodial circumstances is going to look like, in fact may be the same as, so-called “best interest” evidence. But the evidence will be offered to prove that custody should be reexamined. The fact that it will also be relevant if the court reaches the issue of who receives custody does not render the evidence irrelevant to the change-of-circumstance question.
2. The current rule is entirely capable of accommodating the case where custody was initially determined by stipulation or default. All that is required is that the parties offer evidence as to the circumstances giving rise to the original custodial placement and to a change therein which renders the continued placement detrimental to the child.
The threshold standard requiring a change in circumstances is designed to create a rebuttable presumption in favor of stability, and our case law has consistently urged trial courts to apply it with flexibility and common sense. I would have no difficulty affirming the trial court’s findings regarding the necessary change of circumstances in this case. The mother’s living circumstances and support sources changed rather dramatically over the period during which she had legal custody. The addition of another child and the resulting stress, shown in this case to have had a direct and substantial impact on the quality of Stephanie’s care, were sufficient under our cases to permit an examination of Stephanie's best interest regarding future placement. Hogge, 649 P.2d 51 (Utah 1982); Kramer v. Kramer, 738 P.2d 624 (Utah 1987).1
*607In conclusion, I think that the abandonment of the changed circumstances standard as a threshold concern in custody disputes is unnecessary in this case and a step backward in the law.
ZIMMERMAN, J., concurs in the concurring and dissenting opinion of DURHAM, J.. I specifically take issue with the attempt in the majority opinion to transform dictum in concurring opinions in Kramer v. Kramer, 738 P.2d 624 (Utah 1987) about the nature of the change-of-circumstances rule, into the holding of that case. Footnote 5 of the majority opinion in Kramer made it clear that the entire Court agreed on the existence of "exceptional sitúa-*607tions where a change in the circumstances of the noncustodial parent may be relevant to a determination of whether the custody issue should be reopened.” Further, the entire Court agreed that "an inquiry into the effects on the child of the established custodial relationship as it has developed over time is an entirely proper focus for a change-of-circumstances inquiry under Becker and Hogge."