Final answer:
The concordance rate among identical twins for bipolar disorder is higher than the concordance rate among identical twins for major depressive disorder.
Step-by-step explanation:
The correct answer is a) higher than.
The concordance rate refers to the percentage of pairs of twins in which both twins have the same condition or disorder. When comparing the concordance rate among identical twins for bipolar disorder and major depressive disorder, studies have consistently shown a higher concordance rate for bipolar disorder. This means that identical twins are more likely to both have bipolar disorder compared to major depressive disorder.
For example, research studies have reported a concordance rate of around 70-90% among identical twins for bipolar disorder, while the concordance rate for major depressive disorder has been found to be lower, ranging from 10-30%.