New renters are paying on average 16% more than existing tenants, ESRI research has found.
Nationally the raw average monthly rent, not taking account of differences in property type and size, was €214 lower for existing tenancies registered between April to September last year than for new ones.
These gaps are lower in Dublin and higher in the rest of country.
"In percentage terms we actually see much bigger differences in other parts of the country - particularly in parts of the north, north-west and the midlands," she said.
"The biggest differences we see would be in Limerick city, in Waterford city and also in Carlow.
"We've seen the most rapid increases in new tenancy prices occurring outside of the major urban areas.
"This period that we're looking at covers the start of the academic year; and I think it really is quite indicative of perhaps the shortage of accommodation, particularly in larger properties for student house shares."
Dr Slaymaker said Rent Pressure Zones could also be a factor.
"Generally the smaller differences between what new and existing tenants are paying are mostly in the east of the country - Dublin and surrounding counties," she said.
"[This] could be an indication of the Rent Pressure Zones in those areas relative to where we're not seeing Rent Pressure Zones in place elsewhere," she added.
In the capital, more than one-in-five existing tenancies are above €2,000, compared to nearly two-fifths of new tenancies.
Around one-quarter of new tenancies in the capital are priced at €1,500 or less compared to two-in-five existing ones.
The largest gaps between the rents paid by sitting and new tenants are found in the north-west, west and parts of the midlands.