As previously noted, "taxable income" does not include the largest source of income for many retires: tax-free superannuation.

Nor does it tell us much about the overall wealth of those claiming refundable franking credits.The Grattan Institute's Ms Wood said analysing the changes by focusing on taxable income did little to explain the economic position of those affected by the policy change.

In a recent submission to a House of Representatives Inquiry, the Grattan Institute gave the following example."Take the example of a self-funded retiree couple with a $3.2 million super balance, plus their own home, and $200,000 in Australian shares held outside super.

Even drawing $130,000 a year in superannuation income, and $15,000 a year in dividend income, they would report a combined taxable income of just $15,000 and pay no income tax whatsoever."

Calculations by the Grattan Institute show when superannuation income is removed from ABS income and wealth survey data (reflecting taxable income), almost half of the wealthiest 10 per cent of those over 65 report income of less than the $18,200 tax free threshold and thus pay no tax.

On average, however, this group had wealth of nearly $2 million, even before factoring in the value of their home or other property assets.

This illustrates the extent to which individuals with relatively high levels of untaxed incomes (including from superannuation) and wealth have low taxable incomes.

According to the Parliamentary Budget Offices estimates, there are some 320,000 pensioners and allowance recipients who claim refunds for excess imputation credits.

Those estimates show the guarantee would reduce revenue by $300 million in 2021-22, or just 5 per cent.

The relatively small loss of revenue due to the guarantee in itself suggests most of the revenue from the policy is not coming from full or part pensioners, but wealthier retirees.