According to current epidemiological surveys around the world, the prevalence of bipolar disorder is much lower than that of depression. In the United States, for example, the (lifetime) prevalence of depression is about 17%, while the prevalence of bipolar disorder is less than 4%. This figure is very high, and a disease with a prevalence rate of more than 1% is a high prevalence disease. There is another set of data: an experiment was done in the United States, in which about 200 cases of depression, diagnosed 15 years ago, were followed up longitudinally for a long time. By the end of 15 years, about 50% of the patients who were diagnosed with depression were found to be not depressed but bipolar 15 years later. Because in the diagnosis of bipolar, there is an important criterion that you can only diagnose bipolar if you find a hypomanic or manic episode. If this high mood is not found and the patient has never presented before and he has a depressive episode every time, then only depression can be diagnosed. For example, if the onset of depression is around 20 years old, there is no high mood manifestation before the consultation. Although the possibility that getting depression at such a young age may be a risk of bipolar in the future is high. But even so, depression has to be diagnosed according to the diagnostic criteria. Wait for when a high mood episode occurs before changing the diagnosis. This is a current state of medicine and a worldwide problem. But there are some clinical high-risk factors that appear, which may be considered even if a depressive episode occurs at that time, but the possibility of bipolar is high, but these factors are also only a suggestive factor, not a factor for diagnosis. For example, age, if a depression with very early onset is very likely to be bipolar in the future. The average age of onset of depression is around 35 years. The average age of onset of bipolar is 10 years earlier. And more than 50% of patients with bipolar disorder will have an onset over the age of 20. So a single factor like age helps doctors to a large extent to determine what the person will be like in the future.