The Prevalence and Causes of Misdiagnosis. Unfortunately, Andy’s misdiagnosis is not an extreme case or an aberration. According to Drs. Tanvir Singh and Muhammad Rajput, 69% of people with bipolar disorder are initially misdiagnosed with another mental health disorder, most commonly unipolar depression. More than 30% of those remain misdiagnosed for 10 years or more and the average patient remains misdiagnosed for 5.7-7.5 years.