HM Chief Inspector of Prisons for Scotland Brigadier Hugh Monro told the
evidence was needed in terms of the risk of releasing sex offenders into the community.
Brigadier Monro said : "We are releasing I think, in the previous 12 months, I think somewhere around 150 sex offenders directly from closed conditions not having been tested under open conditions.
"Now I don't know whether this is right or wrong,what I am saying is we need some evidence and some help in this matter."
The chief inspector was giving evidence on his
HM Chief Inspector of Prisons for Scotland Annual Report 2011-12
on 20 November 2012.
He welcomed the creation of a draft strategy for managing sex offenders sent to Dumfries prison, being compiled by the Scottish Prison Service.
Brigadier Monro also criticised the "so called back cells" at Cornton Vale prison where women were segregated, which he described as "utterly, utterly shocking and quite horrible".
He said there was now a new unit but questioned why it took three years to build it, as "a morning in those cells was too long".
The chief inspector also called for better training of staff to allow them to take on a mentoring role for prisoners and improve rehabilitation and for prisons to have better family contact centres that gave more than an "arm and a cup of coffee" but addressed family issues like dyslexia.
The report calls for more work in jails to 'cut reoffending' and states that prisoners needed access to purposeful activities.
It says: "If prisoners, including those untried or un-sentenced prisoners on remand, are not participating in purposeful activities during the day, there is much less likelihood of them being prepared for release back in to the community.
"If Scotland is to reduce re-offending, then prisoners need as much access to purposeful activities as possible."
His report came as figures were published showing re-offending rates in Scotland have fallen to a 13-year low.