The decision to take one's own life is both excruciatingly personal and impersonally demographical.
Someone who is in a deep depression may reach a point of hopelessness at the same moment he happens to pass by a bridge, leading to an impulsive, tragic decision that even he may not have foreseen.
On the other hand, societal trends are well-known: elderly people commit suicide at rates that are 50 percent higher than young people, whites nearly three times more than blacks, men nearly four times more than women.
This mix of factors makes year-to-year changes in suicide rates difficult to interpret. The most recent numbers, however, clearly show a small but steady increase over the last few years.
The difference represents only a few thousand deaths nationwide, adding up to a change in rate from 10.9 per 100,000 population (in 2004, 2005, 2006) to 11.7 per 100,000 (in 2009, based on very preliminary data). But that was enough to move suicide into the list of top 10 killers, down from No. 11 (blood infections) for the first time since classifications changed in 1999.
"Other causes of death we seem to be getting a better handle on. They seem to be going down and suicide seems to be going up," said Ann Haas, a medical sociologist and director of prevention projects for the American Foundation for Suicide Prevention in New York.
Movement in national suicide trends often results from specific factors in different age groups and other demographics. Alex Crosby, an epidemiologist who works with suicide data at the Centers for Disease Control and Prevention, said he had not yet analyzed the most recent numbers because they were preliminary and would have more meaning as part of multiyear trends.
But some of the emerging trends he identified a few years ago among subgroups appear to be continuing or even increasing: The relatively low rate of suicides among ages 15 to 24, which rose slightly several years ago, did not decline in 2008 or 2009.
Perhaps the most dramatic trend is not new but has now continued to increase for a decade: The suicide rate among ages 45 to 64 grew 28 percent between 1999 and 2009, surpassing what for years was the most suicide-prone demographic, the elderly.
Unemployment and financial anxieties could play a role. And they tend to go along with factors such as substance abuse and family problems that also are known to affect suicide.
"One of the times in the United States when we had some of the highest suicide rates" - double today's - "was during the Great Depression," Crosby said.
Military suicides have spiked during the wars in Iraq and Afghanistan; the Army's rate appears to have exceeded that of civilians in 2008 for the first time. They also have served to increase awareness of the issue, something that experts have been struggling to do for years.
"Veteran and military suicides in a very poignant way have opened that discussion," said Haas, of the suicide-prevention foundation. "These people have defended the country, and they come home and they are not getting the treatment that they need. I think it has really called national attention to the fact that this is not OK."
Statistics help to define and publicize, but they do little to explain individual cases. By far, the biggest risk factor for suicide is mental illness, both short- and long-term.
Almost no one commits suicide during a period of mental stability. On the other hand, only a tiny percentage of mentally ill people take their own lives.
It is in those cases, however, that broader factors come into play. Access to treatment - or just other people to talk to - makes a death less likely. Access to lethal methods makes it more so.
Pennsylvania's suicide rate, for example, is around the national average. New Jersey's typically is among the lowest.
Breaking those statistics down by mechanism used shows that the two states are virtually identical on every means - poisons, hanging, jumping - except one: Pennsylvania's rate of suicide using firearms is more than triple New Jersey's.
People who say they plan to kill themselves and have the means are at the highest risk and should be taken seriously, according to experts.
"Engage in conversation with that person in a way that is nonjudgmental and compassionate," said retired psychologist Norman Weissberg, training director for Contact of Greater Philadelphia, a suicide-prevention organization, "and recommend that they seek professional help."
Phone: The National Suicide Prevention Lifeline is staffed around the clock: 1-800-273-8255.
Online: The website includes warning signs, information for veterans, and local crisis centers: www.suicidepreventionlifeline.org