GRA president John Parker has said that new crime categorisation guidelines has led to the "massaging" of statistics.
Official figures have pointed to drops in various categories of crime, but Parker said that new guidelines were issued by Garda management about two years ago on re-categorising crimes.
"These days we often see where a window is broken, and it's obvious that there was entry gained but nothing was taken - a lot of these are put down as criminal damage," he said.
"Crime categorisation itself is a skill, and it's easy to massage statistics."
He said that, for instance, it may look like there has been an increase in the number of checkpoints on the road - but the fact is the duration of each checkpoint has been halved.
He also said that morale within the force is at rock bottom because of cutbacks - which mean gardaí can't do their job properly.
"You turn up to the scene of a crime and [you make] a half-hearted effort because of the lack of facilities there," said Parker.
"It's a PR exercise."
Around 170 rank and file members of the Garda Representative Association have gathered in Westport in Co Mayo for their annual conference.
Much of today's session will be dominated by motions on a new independent policing authority and an independent commission to examine garda pay and conditions.
The Garda Commissioner Martin Callinan will address delegates this evening.