He found that male suicide rates over the past century rose and fell with unemployment - starting at around 20 for every 100,000 males before World War I; peaking at 27.5 in the 1930s Depression; halving to between 10 and 15 through what he calls "the Long Prosperity" from 1940 to 1974; and doubling to around 25 per 100,000 when unemployment peaked again late in the century.
Remarkably, the female suicide rate was much lower and more stable, apparently immune to economic cycles.
The contrast reflects the deeply ingrained role of paid work in the male sense of self-worth.
Men despaired not just when they lost their jobs in recessions, but also when personal misfortunes ended their ability to be providers.
Others, especially the elderly, chose to die because they could not stand the burden they placed on their families.
Alcohol was also a common factor in suicides, especially before World War I when people drank strong spirits. Later, other drugs also undermined people's will to live.
For most of the century, the highest suicide rate by age was for men in their 40s. That changed dramatically in the 1980s, when young people became prominent for the first time. This time unemployment was cushioned by the welfare state for older men, but hit young people hardest because they couldn't get that all-important first job.
The impact played out in relationships. In Professor Weaver's words: "The most startling increase in the proportion of suicide motives for this substantial group involved marital or romantic factors.
"This generation was the first to grow up amidst a substantial number of fractured families," he writes. "With that came a weaker sense of security."
Since 2000, suicide rates have fallen slightly. The female rate has stayed stable around 5 per 100,000. The male rate dropped from 24 per 100,000 in 1998 to 17 in 2011.
Suicide rates for the middle-aged are trending downwards, and for those aged 65-plus they are now the lowest on record.
But the rate is still highest at the ages 15 to 24 - 28 per 100,000 for young men, and 10 for young women. The history of the past century suggests jobs and constantly engaged parents are the keys to getting those rates down again.
* Name has been changed.
Spiritual crisis, says counsellor
Suicidal thoughts have become common among Kiwi teenagers, but supportive parents and counsellors can help, Pakuranga College counsellor Francis Jamieson says.
Mr Jamieson, 49, has distilled his 31 years of counselling experience into a 77-page book, A Practical Guide to Working with Suicidal Youth.
He said youth culture had changed since he was young.
"In my day, we used to talk about running away from home," he said.
"These days, kids talk about committing suicide more than running away from home ... They say 60 to 70 per cent of New Zealand youth in high school at some stage contemplate it."
Mr Jamieson believes it reflects a spiritual crisis.
"I think it's getting harder for a lot of our kids to look at the world and figure out their place within it. There is so much going on, there is so much distraction.
"I think a lot of our youth are quite divorced from the beauties of nature, the privilege of being alive and really simple things."
A Practical Guide to Working with Suicidal Youth, Francis Jamieson, Xlibris, $20.74 (printed), $3.31 (e-book).
• Professor John Weaver will give a public lecture in Room S.1.01 at Waikato University in Hamilton at 6pm on Wednesday.
Sorrows of a Century: Interpreting Suicide in NZ, John Weaver, Bridget Williams Books, $59.99.
