5-9 Bipolar disorder is a disabling mental illness that is characterized by episodes of elevated or irritable mood and depression. Lithium carbonate has been the standard therapy for treating bipolar disorder. In more recent years lithium has been replaced with sodium valproate because of a wider range of useful doses and fewer side effects. The BALANCE investigators* conducted a randomized open label (in which the subjects and investigators knew who was taking which drug) clinical trial comparing valproate in combination with lithium with valproate alone. The end point was having an emergent mood episode during a 24-month period. Fiftynine (54%) of the 110 people in the lithium group and 76

(69%) of the 110 in the valproate group had events during follow-up. What is the relative risk for an event for people being treated with valproate compared to lithium (the tradi-