December, 2000 - A Mayo Clinic study published in the December issue of the American Journal of Psychiatry debunks the commonly held notion that about 15 percent of people diagnosed with depression will commit suicide. After analyzing 100 suicide studies conducted over the past 30 years, Mayo Clinic researchers concluded that a more accurate suicide rate for patients with depression is 2 to 9 percent.
"A 15 percent suicide rate means that of six patients diagnosed with depression, one will commit suicide during his or her lifetime," says John Michael Bostwick, M.D., a Mayo Clinic psychiatrist and lead researcher on the study. "That's simply not true."
Hierarchy of risk
The study found a stair-step hierarchy of suicide prevalence based on a patient's treatment history. A physician's clinical judgement about the level of treatment intensity required is a good indicator of who is at highest risk of suicide.
- Patients recently hospitalized for suicide after a suicide attempt or with suicidal thoughts were at the highest risk level, 8.6 percent.
- Next were other patients with depression who had been hospitalized -- but not for suicide. Their risk of suicide was 4.1 percent.
- Outpatients treated for depression had a suicide risk of 2 percent.
- The risk for the general population is 1 percent.
"Finding that hospitalized patients are at highest risk may seem like stating the obvious, but despite thousands of studies, almost no definitive risk factors have been found to tell us who is most likely to commit suicide," says Dr. Bostwick. "From the public health perspective, the study shows that most effective suicide prevention efforts should target recent or repeatedly hospitalized patients." Why suicide rates are overstated
The 15 percent suicide rate, based on a 1970 study, is used in standard American medical school text books. It's too high, says Dr. Bostwick, because of a skewed statistical analysis. Dr. Bostwick explains the error using an example of 100 patients diagnosed with depression. After five years, 10 patients die and five of the deaths are from suicide. Using the standard method of calculating the deaths by suicide -- called general mortality prevalence -- the suicide rate is five out of 10 or 50 percent, even though 90 patients are still alive.
The Mayo Clinic research argues that the suicide rate should be calculated using a method called case fatality prevalence. For this example, that result would be 5 out of 100 or 5 percent.
"It's a magnitude of difference," says Dr. Bostwick. "Using this approach, the numbers show that suicide continues to be rare. The intent isn't to minimize the pain caused by any individual suicide -- it's devastating -- but rather to look at the prevalence more critically."
Another reason that the 15 percent suicide rate is no longer relevant is because the definition of depression has changed. In 1970, only people with serious mental illnesses (such as manic depression) were diagnosed with depression. Today the diagnosis has been greatly expanded to include many people with mild to moderate symptoms that can be treated by medication or therapy. Under this broader definition, up to 20 percent of Americans could be diagnosed with depression.
"We know that everyone who is diagnosed with depression shouldn't be treated the same," Dr. Bostwisk says. "This study gives physicians and families a more accurate picture of suicide risks and prevalence and helps minimize some of the hysteria that can come with a depression diagnosis."
