Hourly wage growth was lagging behind CPI inflation, with real wages falling the most in the third quarter of this year since GST was increased in 2010, Robinson said.
It was normal for wage growth to lag price inflation because pay rises were often benchmarked to the cost of living.
"But when prices are rising so quickly, such backward-looking and infrequent adjustments can actually have big impacts on household purchasing power," he said.
"On an annual basis hourly earnings were down about 1 per cent in [the third quarter]," he said.
"So even though wage inflation has picked up over the past year, it just hasn't been anywhere close enough."
The Household Living-Cost Price Indexes (HLPI) published by Stats NZ offer a breakdown of inflation with costs weighted to reflect the reality for different demographic groups.
"What's immediately clear from the data is that households have historically had varied experiences of inflation," Robinson said.
"Over most of the last decade, beneficiaries and superannuitants saw their living costs rise at a faster rate than average."
For example, the 2021 expenditure weights calculated by Stats NZ showed that 16.4 per cent of expenditure of the lowest-income households went towards rent payments, versus just 6.7 per cent for those on higher incomes.
"So when the price of renting goes up, that will have a larger impact on the cost of living (and HLPI) of lower-income households than for higher-earnings ones."
The 20 per cent of households with the lowest incomes had tended to see the largest living cost increases, while the richest 20 per cent have seen the smallest increases.
The cumulative impact was quite significant, he said.
Since the second quarter of 2008, living costs for the top 20 per cent of earners have risen 20 per cent, but for the lowest 20 per cent the increase has been 30 per cent.
Superannuitants have had it the worst in terms of the rising cost of living, with costs up 34 per cent over the same period.
More recently widespread inflation had flattened the differences with cost increases of about the same magnitude for all households, he said.
But while "on paper" it looked like everyone was currently hurting from the same strong inflation, digging further revealed that for poorer households, high inflation was still particularly hard to deal with.
The biggest drivers of strong inflation in recent quarters had been housing, transport and food, Robinson said.
"These are all essential items - and that makes absorbing price rises more difficult for poorer households, since a larger share of their expenditure goes towards essential goods and services."
It was easier for higher-income households to cope with price rises because they could simply cut back on more discretionary spending (such as not eating out as much), he said.
"But for a poor household whose budget can barely cover the essentials even when inflation is low, the choice quickly becomes: do I have lunch this week or pay the rent?"
Ultimately the data highlighted why it was crucial that the Reserve Bank was proactive about raising interest rates "to slow the economy and put downward pressure on inflation", he said.
Robinson acknowledged that interest rate costs weren't trivial, representing between 3 and 7 per cent depending on household wealth.
"But considering the rest of the CPI basket is all going up steeply, the biggest threat to your real income and purchasing power is actually inflation."
