In its review of the use of stop and search tactics by Police Scotland, the Scottish Police Authority (SPA) found they contribute to tackling violence and antisocial behaviour in Scotland.

This is open to question. Evidence that policing policy has made a substantive difference to the decline in violent crime in Scotland, or England, or other parts of Europe is limited to non-existent. It is a prevailing trend in much of the Western world, regardless of local policing policy.

Perhaps this is one reason why the SPA notes a vagueness about justification for using stop and search. Its report points out that neither officers nor communities are really clear whether the goal of stop and search is to deter crime or to reduce it.

The justification matters because there is a danger here too. The SPA concludes there are risks in the way the tactic is applied, and how it affects different groups - particularly young people and certain communities.

Happily there is no evidence of ethnic minorities being disproportionately targeted. But there is an emphasis on stopping and searching young people - those aged 15 to 19 are more likely to be stopped, and one-third of all stop and searches were carried out on older children and teenagers.

While young men in particular are more likely to commit crime, there are people within and without the police who are uneasy that excessive application of this policing tactic could undermine the force's relationships with younger people.

There are also significant civil liberties issues here. If members of the public, especially young people, are to be stopped on a voluntary basis, it is vital that they realise this.

There is a difference between statutory stop and search, when police have reasonable cause to search a person, an non-statutory stop and search, to which a person can refuse to submit.

But there is no consent if people do not know the difference. The power imbalance between a police officer and a young person for example is such that the latter is not likely to challenge a demand that they submit to a search - unless it is clearly explained that they can.

There have to be questions about the ability of younger children to give informed consent at all to searching.

A lack of reliable statistics about the issue has been one of the complicating factors of the debate. Figures showing more than 500 children under 10 being stopped and searched in a single year - including dozens under the age of seven - are alarming.

But it has not always been clear in the past what constitutes a stop and search. The idea of the consensual search needs serious reconsideration and may be untenable. The Scottish Government should also look at the case for extending statutory powers to cover searching young people for alcohol.

However, the SPA is right to say there needs to be a great deal more transparency to protect public confidence, and in the mean time police training is essential so those who are able to decline to submit to searching know they have that right.