Robert Cialdini also brings the same theory in his book Influence. Not only that a tragedy prompts other to the same action, but he showed some studies where a type of tragedy prompted a seemingly irrelevant event.
For example, 2 days after a suicide appearing on the news, it is significantly (don't remember the exact numbers) more likely for there to be a plane crash. He attributes this to the fact that some pilots that have had suicidal thoughts are triggered by the suicidal news.
Another interesting study looked at how mortality rates of car accidents are higher after suicide-related news. This study found a surprising number of car deaths in which the driver was stepping on the gas pedal, instead of the break, which might be an indicator of suicide.
For example, 2 days after a suicide appearing on the news, it is significantly (don't remember the exact numbers) more likely for there to be a plane crash. He attributes this to the fact that some pilots that have had suicidal thoughts are triggered by the suicidal news.
Another interesting study looked at how mortality rates of car accidents are higher after suicide-related news. This study found a surprising number of car deaths in which the driver was stepping on the gas pedal, instead of the break, which might be an indicator of suicide.