The State's most recent immigrants are more highly educated than their Irish counterparts, with over 40 per cent of those who arrived in 2004-05 having a third-level qualification, yet not as highly educated as earlier arrivals, new figures have shown.

The corresponding figure in the indigenous population is below 30 per cent.

The figures appear in a study of immigrants' educational profile to be published today by the Economic and Social Research Institute (ESRI) in its quarterly economic commentary.

"The earlier cohorts appear to have higher levels of educational attainment relative to both the most recent arrivals and the native population," the report states.

While advising caution in interpreting the figures, which capture only those who arrived in the Republic and stayed, the authors note: "Either way, the pool of immigrants in Ireland remains highly educated and the most recent arrivals continue to add to the highly educated pool."

A separate investigation found that the "occupation gap" - the observation that immigrants tend to be found in lower level occupations than Irish nationals - tends to fall the longer an immigrant spends in the country.

The most recent immigrants are 13.4 per cent less likely to be in managerial, professional or associate professional occupations. For earlier arrivals, however, the gap is lower, and for those who arrived between 1995 and 1999, there is no gap.

Accounting for these patterns, the authors suggest that immigrants may assimilate over time by learning English or other useful skills, while it could be that those who arrived earlier but did not succeed in the labour market left, thereby leaving a pool of "successful" immigrants.

A further possibility is that the nature of the Republic's immigrant population has changed over the past 10 years. "Earlier cohorts might have performed better on arrival and might have continued to do so while later arrivals might have performed worse and might continue to do so," the report suggests.

The latest ESRI research is based for the first time on data showing the year of immigrants' arrival in the Republic, and as such provides a more reliable picture to that of previous studies.

As it shows the "occupation gap" not to be a long-run feature of immigration, the authors point out, "concerns about under-utilised potential seem to have been misplaced".

The report notes that earlier analysis led to the conclusion that immigration policy should include an integration strand to assist immigrants in overcoming initial problems in the labour market.

"The analysis here suggests that the initial problems disappear either because people re-emigrate or assimilate," it states. "Hence, the need for policy interventions is lessened, although they may still be needed for specific groups."