An international test shows adults' literacy and numeracy has fallen significantly over the past eight years.

Results from the OECD's international Survey of Adult Skills in 31 OECD nations last year showed this country's scores were about average for literacy and below average for numeracy.

New Zealand's 16-65 scored an average of 260 for literacy, 256 for numeracy and 249 for "adaptive problem solving".

The scores were well-behind those of league table leader, Finland, with average scores of 296 for literacy, 294 for numeracy and 276 for problem solving.

They were also lower than the previous round of tests, with a 21-point drop in literacy and a 15-point drop in numeracy.

A quarter of New Zealand adults were reading and writing at the lowest level of proficiency, double the figure recorded in 2015 and 13 percent performed at a high level, slightly fewer than in 2015.

In numeracy 28 percent performed poorly, up from 19 percent, while 12 percent were good at numeracy, down from 15 percent.

The report indicated that increased immigration had affected New Zealand's results.

"Between 2014 and 2022-23, the proportion of foreign-born adults of foreign-born parents grew by about 7 percentage points in New Zealand. Over this same time period, the declines in literacy proficiency were more pronounced for foreign-born adults than for native-born adults in New Zealand, and the literacy gap between the two groups widened.

It also found New Zealand's gender differences were larger than the OECD average in literacy but smaller in numeracy.

"On average, across participating OECD countries and economies, women displayed higher average proficiency than men in literacy (by 3 points), while men scored higher in numeracy (by 10 points) and adaptive problem solving (by 2 points). In New Zealand, a significant 12 points difference in favour of women was observed in literacy; no significant difference was observed in numeracy; and no significant difference was observed in adaptive problem solving."

The report said in all countries higher levels of education were associated with greater proficiency in literacy, numeracy and problem solving.

"In New Zealand, among adults aged 25-65, those with tertiary education scored 29 points higher in literacy than those with upper secondary education (OECD average: 33 points), and those with upper secondary education scored 48 points higher than those with less than upper secondary education (OECD average: 43 points)," the report said.

The survey also measured differences between age groups.

"Older adults (aged 55 to 65) in New Zealand displayed lower proficiency than 25-34 year-olds in adaptive problem solving, and similar proficiency in literacy and numeracy. On average across OECD countries, adults aged 55-65 scored below 25-34 year-olds in all domains (by 30 points, in literacy). Skill gaps between older and younger adults could reflect ageing effects, but also differences in the quality and quantity of education and training across generations."

The report said 33 percent of New Zealand workers were over-qualified for their job, compared to the OECD average of 23 percent, and 34 percent were over-skilled.

"About 10 percent of workers report that some of their skills are lower than what is required for their job (OECD average: 10 percent). In New Zealand, they often say this is because they need to improve their computer or software skills (50 percent), followed by project management or organizational skills (39 percent)," it said.

"In OECD countries, adults who are overqualified for their job incur significant economic and social costs. This is less the case in New Zealand: on average, their wages are 17 percent lower than peers in well-matched jobs who have similar educational attainment (OECD average: 12 percent lower). However, they are not significantly less likely to report a high level of life satisfaction (OECD average: 4 percentage points less likely)."

-RNZ