A suicide note or death note is a message left behind when a person dies by suicide, or intends to die by suicide. A suicide note or death note is a message left behind when a person dies by suicide, or intends to die by suicide. It is estimated that 25–30% of suicides are accompanied by a note. However, incidence rates may depend on ethnicity and cultural differences, and may reach rates as high as 50% in certain demographics. A suicide message can be in any form or medium, but the most common methods are by a written note, an audio message, or a video. Some fields of study, such as sociology, psychiatry and graphology, have investigated the reasons why people who commit, or attempt, suicide leave a note. According to Lenora Olsen, a professor at the University of Utah School of Medicine, the most common reasons that people contemplating suicide choose to write a suicide note include one or more of the following: Sometimes there is also a message in the case of murder–suicide, explaining the reason(s) for the murder(s), see for example, Marc Lépine's suicide statement and videotaped statements of the 7 July 2005 London bombers.