Why do young men end up in prison and what would help keep them out?

It's a topic which has occupied the minds of researchers and those working in criminal justice for years.

A new report from the Centre for Youth and Criminal Justice (CYCJ) at Strathclyde University suggests some answers, but poses a lot of questions too.

Youth offending, like all crime, is declining, and we tend to overestimate how bad the problem is. The researchers point out 95 per cent of young people never offend at all.

But young adults aged 18-20 have around three times the conviction rate of the general population and among 16 to 17-year-olds the rate is nearly double the national average.

Those aged up to 21 whose offending is serious tend to wind up at HMYOI Polmont, so the young offenders' institution is an obvious place to look for answers.

The report is based on reviewing files and interviewing 125 young men and details some troubling findings. They came from backgrounds of trauma and loss, with parental deaths, domestic violence and parental separation affecting 59 per cent, while 80 per cent had been excluded from school. Substance misuse was common with 48 per cent regularly using illicit drugs.

Could anything have helped prevent their arrival in detention? At least two-thirds had been before the Children's Panel at some stage. But the report finds many didn't really understand why they were being detained, and most were facing the same challenges when they left as when they entered custody.

The researchers conclude better educational resources could help. While most had a lousy experience of schooling, the study found few prisoners were hostile about learning.

The report also draws conclusions about alternatives to custody. It wasn't clear how many prisoners had been offered community-based alternatives, but several were sceptical about it. "I'm used to being locked up, jail doesn't bother me," said one.

All court reports should offer alternatives to custody for consideration, the study says.

Secure care may offer a better option for younger offenders. But it is hugely more costly.

But should we lock up young offenders at all? Another CYCJ report called for a total rethink of youth justice in Scotland. Sounds unrealistic? Perhaps, but in Finland in 2007 just three young people were sentenced to custody, while Sweden detained only one in 2009.