When 2 medical conditions occur together more often than predicted by chance, they are called comorbid conditions. The observation that depression is connected to epilepsy (i.e., that they are comorbidities) raises many questions. How are the illnesses connected? Are both caused by a common underlying brain abnormality? Is there an abnormality of neurotransmitters responsible for both? Finally, does the same connection occur with other chronic medical illnesses? The authors of this study used asthma, another chronic medical illness, as a comparison. They looked at the rate of depression in people with asthma and compared this with that in people with epilepsy. Using the registry data, they were also able to look at the opposite possibility: that is, do people with depression have epilepsy more often?