While Robin Williams’ suicide came as an unfortunate surprise for family, friends, and members of the general public, certain aspects of Williams’ personality may have served as the writing on the wall for his untimely death. Aside from his history of depression and addiction, some experts agree that Williams’ comedic abilities were tell-tale signs of depression and bipolar behaviors, keeping up with the “sad clown” façade. There are some other personality traits people exhibit that can indicate their risk for attempting suicide.

1. Smokers

It seems as though smoking cannot only deteriorate our physical health, but also our mental health. Researchers from the Washington University School of Medicine noticed that a rise in cigarette taxes coincided with a drop in suicide rates, so they decided to examine the possible relation to these statistics. Using data from the National Center for Health Statistics, the research team first decided how many suicides were committed by people who identified as smokers. The second part of their analysis focused on the number of suicides in states with aggressive anti-smoking policies. For each dollar increase on cigarette taxes each year, the suicide rate for that state dropped by 10 percent.

“We really need to look more closely at the effects of smoking and nicotine, not only on physical health but on mental health, too,” said lead researcher Dr. Richard A. Grucza. “It could be that [smoking] affects depression or increases addiction to other substances. We don’t know how smoking exerts these effects, but the numbers show it clearly does something. Nicotine is a plausible candidate for explaining the link between smoking and suicide risk. As with other drugs … chronic use can contribute to depression or anxiety, and that could help to explain the link to suicide.”

2. Teens Who Suffer A Concussion

Suffering a traumatic brain injury (TBI) can damage a teenager’s neurological health as they grow up, but could that also relate to a weakened psychological and emotional state? A recent study conducted at St. Michael’s Hospital in Ontario found that teenagers who experience a TBI such as a concussion are at an increased risk to premature death, most notably due to suicide. Teens who suffered a concussion were three times more likely to attempt suicide, twice as likely to be bullied at school, and more likely to call a crisis help-line or to be prescribed drugs to treat anxiety/depression compared to those who did not suffer a concussion.

"These results show that preventable brain injuries and mental health and behavioural problems among teens continue to remain a blind spot in our culture," said lead author of the study Dr. Gabriela Ilie. "These kids are falling through the cracks."

3. Musicians

Kurt Cobain’s personal history of drug abuse and family history of suicide were both indicated as risk factors for his eventual suicide, but not many psychology experts were quick to suggest his career as a musician was a red flag. Steve Sack, director of the Center for Suicide Research and a professor at Wayne State University, explains that suicide rates among musicians are three times higher than the current national average. While many studies on suicide agree that other artistic professionals such as writers, actors, and painters are prone to depression and suicidal thoughts, musicians tend to go unnoticed. Yet their work is of a similar nature.

4. Adults With Asperger’s

Falling under the umbrella of autism spectrum disorders (ASD), Asperger’s syndrome is a condition that causes people to suffer from social impairment, communication difficulties, and restrictive/repetitive behaviors. The recent study of the UK population revealed that people with Asperger’s are nine times more likely to have suicidal thoughts and many even attempt suicide at some point in their life. The inability to socialize or connect with other people exhibited by those with Asperger’s was deemed a contributing factor to suicidal thoughts.

"Adults with Asperger Syndrome often suffer with secondary depression due to social isolation, loneliness, social exclusion, lack of community services, under-achievement, and unemployment. Their depression and risk of suicide are preventable with the appropriate support,” Simon Baron-Cohen, professor from the Autism Researcher Center at Cambridge University, and the CLASS clinic in the Cambridgeshire, said in a statement. "This study should be a wake-up call for the urgent need for high quality services, to prevent the tragic waste of even a single life."

5. Adopted Teens

As a result of detachment and placement in an institutional setting at an early age, many adopted teens can display signs of various psychiatric disorders as well as substance abuse. A recent study including over 1,200 teens living in Minnesota revealed that 47 out of the 56 suicidal attempts were carried out by those who were adopted. Sixteen of the adopted teens who attempted suicide were boys and 31 were girls. Among the 692 adopted teens included in the study, the majority suffered from a range of behavioral issues such as a family discord, academic disengagement, externalizing behavior, and a negative mood. Surprisingly, the research team associated suicidal thoughts with psychological traits inherited form their biological parents, including psychiatric disorders and substance abuse rather than problems with their adopted home.

“Adolescence, in general, is a period of higher risk [for suicide attempt],” Dr. Victor Fornari, director of child and adolescent psychiatry at North Shore-LIJ Health System, told HealthDay. “And now there’s evidence that the risk may be relatively higher for adopted adolescents.”