Mich. Comp. Laws § 600.2925b: Determining pro rata shares of tortfeasors.

Sec. 2925b.

Except as otherwise provided by law, in determining the pro rata shares of tortfeasors in the entire liability as between themselves only and without affecting the rights of the injured party to a joint and several judgment:

Their relative degrees of fault shall be considered.

If equity requires, the collective liability of some as a group shall constitute a single share.

Principles of equity applicable to contribution generally shall apply.