What are the reasons for a denial of class certification for a medical malpractice class?

The trial court based its denial of class certification in part on its conclusion that secondary factors might require individualized adjudication of the employment issue, without evaluating which of these factors might be amenable to classwide or manageable adjudication, and without evaluating whether any such factors would be of either overriding or substantial relevance when compared to the available classwide proof as to control. These reasons require reversal of the class certification denial based on improper criteria, and remand of the certification question for redetermination using appropriate considerations. (Linder v. Thrifty Oil Co. (2000) 23 Cal.4th 429, 436 [certification may not be denied based on improper criteria].)