Do creative people have more mood disorders? To answer this question, researchers have to compare the instance or rate of mood disorders in creative people to people they consider less creative. Even though these kinds of studies appear to provide fairly consistent support for the creativity-mood disorder link, they are in fact highly controversial among creativity researchers.
Consider the method called autopsy diagnosis. Here researchers examine biographical and historical records to provide a post-mortem diagnosis for eminently creative people. But establishing the presence of a mental disorder for someone who is long-deceased is fraught with uncertainty at every step of the process. To be labelled a creative genius, a person must have creativity and the characteristics that we associate with creativity at that time. So the historical context is crucial. For instance, there are certain time periods for which being moody and irrational was seen as positive evidence of genius itself, particularly for those in the arts. Writers during the Romantic Era sometimes cultivated an ‘aura of mania’ in order to appear possessed of extraordinary ability. These artists were more likely to be recognised for profound creativity, and therefore recorded in the sources that many researchers use today. But there’s no way for us to tell whether that artist was actually suffering from a mood disorder. So whether the characteristics of a creative person just happen to fit the ideology of genius during that time, or whether, as some researchers have suggested, these characteristics are exhibited purposefully to make an impression, they might be more likely to be represented in historical records than someone with equivalent talent and creativity who does not fit this image.