From Max Kennerly at Litigation and Trial, "Mediation Of A Big Injury Case: A Game Worth Playing?"--
[W]hen it comes to serious injury lawsuits against a single defendant — where the only issue is the amount the defendant is willing to pay to settle the case — it’s hard to articulate what, exactly, the mediator can accomplish. Assuming the clients and lawyers aren’t irrational, there’s little for a mediator to work with, there’s just a number on one side and a number on the other.
This quote was pulled from the beginning of Kennerly's post. He goes on to make three "suggestions" for mediation. Here is the first: "Do not mediate unless the defendant has both (a) made a reasonable offer in writing and (b) has agreed to bring a representative with authority to settle at your current demand."
Good advice. For Kennerly's other suggestions, read the full post.