At a royal commission into child sexual abuse in Sydney, the cardinal was asked about the number of abuse cases that had come to him since he took over as archbishop of the diocese.

Data provided to the commission showed complaints had been made about 55 ordained clerics since March 2001, said Gail Furness SC, counsel advising the commission.

The earliest of the alleged offences happened in 1952.

"I'm aware (of that data) but according to our statistics it's inaccurate," Dr Pell said.

He said he had documents that showed there had been 91 complaints but quite a number were multiple complaints about individuals.

"Rather than 55, there were 29 priests so accused," he said.

He offered the commission his data.

Ms Furness asked him to accept the 55 figure for now, which would mean that six per cent of the 842 clergy employed in Sydney since 1952 were sexual offenders.

Dr Pell said he would be surprised if Sydney was two per cent above the national average, which had been assessed by the church at between four per cent or five per cent of clergy.

He stressed that the church's approach had changed.

"The whole general atmosphere has changed radically - we are able to talk about it," he said.

Dr Pell said schools and parishes now encouraged people to report problems.

"In quite a number of cases - say, for example, in our schools - the incidents are not found to be validated and to some extent they are less serious than others," the cardinal said.

Ms Furness pressed him for figures to support that evidence.

Those in the hearing room clapped.

The cardinal's evidence also drew a response from the public gallery when he referred to recent research that showed a significant level of abuse happened in families, normal and blended.

He said his information was based on a newspaper report and he could not remember the detail.