The decision to take a child into state care is always a challenging one, and one which stokes emotive responses.

For social workers and other professionals involved it often feels like an unwinnable decision. On the one hand they face being pilloried for 'snatching' children and breaking up families, on the other they can end up berated for leaving a child at risk, especially in the event of a later tragedy.

But what does removal into care achieve? Remarkably, experts don't always have a clear idea. It is difficult to track the results for a small child taken into foster care, or removed to live with relatives, when they may not be clear for years.

Even if the outcome is known - university? prison? something in between? - it isn't easy to tell what aspect of their lives has led them to go in a positive or negative direction.

Light will be shed on this issue, though, by a new study underway as part of a collaboration between the universities of Stirling and York.

The first in-depth research of its kind, it will focus on children who are looked after away from home by relatives, foster carers or adopters before the age of five.

Talking to carers, adopters, social workers and children, researchers will try to shed light on the experiences of children and the best ways to give them stability and security in the future.

Recent figures suggest that more than 10,000 Scottish children fall into these categories. In 2013, 5,577 children lived with foster carers or would-be adopters, 1,467 lived in children's units and 4,238 were staying in a community placement such as living with relatives, or 'kinship care'.

The study will try to determine which of these options work best and what makes them work. What problems do children experience, what helps and where are there gaps in services?

It could help answer other key questions, such as why so many such children experience frequent moves of placement, how best to help children whose parents abuse drugs, and what causes delays.

One of the lead researchers, Stirling University's Professor Brigid Daniel hopes it will help those responsible for difficult decisions, including social workers, children's panel members, and health and education staff decide what is genuinely likely to benefit the children most.

Crucially, it is a longer term study. Initially funded for three years by the British Association for Adoption and Fostering, it is likely to be more useful the longer it runs. BAAF Scotland director Barbara Hudson says she hopes funding can be found to keep it going for 10-15 years.

"A lot of such research is just a snapshot. But we all live a long time," she says. Like the Seven-Up TV series which has tracked children over decades into adulthood, this could run and run. "I'm an addict of that wonderful series. I'd like to think we've started something which is going to have that kind of significance," Ms Hudson says.