One in five witnesses to crime do not report them, according to a poll conducted for Fine Gael. The TNS/MRBI survey also shows one in three under-25s do not report crimes.
Fine Gael justice spokesman Mr John Deasy said the findings reveal a "black hole" in official crime figures.
Today's figures show non-reporting of crime was highest among 18 to 24-year-olds at 32 per cent and higher still among students at 43 per cent. Mr Deasy said the findings reflect previous surveys indicating "a disappointing, and falling, level of confidence in An Garda Síochána, particularly amongst young people".
The Fine Gael survey of 931 adults carried out between the 10th and 19th February this year also revealed that 15 per cent of the adult population or 430,000 people or members of their household, were victims of crime in the past two years.
Young people in the 18-24 age group were the most common victims of crime at 25 per cent rising to 30 per cent among students in the age group.
Earlier this week, the Irish Independentpublished MRBI figures compiled for the Garda showing levels of public satisfaction with the force had dropped 6 points to 81 per cent.
But an
Irish Timespoll published last month showed 37 per cent of respondents had lost confidence in the force, rising to 59 per cent among young people.