Suppose you saw data that showed that people tended to commit suicide just after they started taking anti-depressants. What would you conclude?
The alleged suicide of Chris Cornell of the music group Soundgarden came with the news that he suffered from depression and was on anti-depressant medication. I was listening to a radio program Here and Now where they were interviewing Kelly Posner Gerstenhaber of the Columbia Lighthouse Project at Columbia University about other reports that suggested that anti-depressants could trigger suicidal thoughts and, as a result, some physicians were refraining from prescribing these medications for their patients with depression and some people with depression were afraid to take them.
Posner Gerstenhaber said that she led a team that had been asked by the FDA to look into whether anti-depressants could cause people to attempt suicide and she said that they found no such relationship and that in fact this medication was the best way to prevent suicides.
So how did this belief that these drugs could causes suicides arise? She said that it is due to an unfortunate combination of facts. One is that it is undoubtedly the case that depression is the main factor that causes people to attempt suicide. The second is that people are likely to seek treatment when they are feeling at their lowest and at the greatest risk. The third is that the medication takes some time to produce improvement.
As a result, many people start taking anti-depressants at the very time when they are most likely to attempt suicide and may attempt it (and sadly succeed) before the medication has had time to produce improvement. Thus you end up with correlational data of suicides that spike just after people begin to take the drugs that suggests a false causal relationship.