But it ain't that simple because both taxes were part of packages where much of the proceeds of the new tax was used to cut other taxes. Money from the carbon tax was used to exempt certain export industries from paying it and to finance a small income tax cut for all individuals earning up to $80,000 a year. The expected proceeds from the mining tax were used to fund a big instant tax write-off for small business, a refund of the tax on super contributions for employees earning up to $37,000 a year and to cover the loss to the taxman when compulsory super contributions are raised from 9 per cent to 12 per cent of wages. So that argument doesn't wash. Going the other way, however, the Libs are right when they remind us that much of the cumulative $150 billion worth of ''savings'' Swan likes to boast about constitutes reductions in tax concessions rather than cuts in government spending. Whenever Swan claims to be a lower taxer than the Howard government, the Libs reply indignantly that tax collections have risen hugely under Labor. As with so many of the claims politicians on both sides make, this is literally true, but calculated to mislead. It's true that, from the total tax collections of $278 billion in 2007-08 (John Howard's last budget), collections first fell to $261billion in 2009-10 (thanks to the global financial crisis) but, on the latest best guess, are to rise to about $335 billion this financial year. That's a net increase of $57 billion, or 20 per cent, over the five years since Howard's last budget.

Convinced? You shouldn't be. Such a comparison looks worse than it is because it ignores the effect of inflation. If we subjected the Howard government to the same trick, we'd say tax collections increased by $163 billion, or 140 per cent, over 12 years. No, we should, at the very least, allow for inflation and look at the real increase in tax collections. By my rough figuring, using the implicit price deflator for gross domestic product, the real increase in tax collections is about 10 per cent. That's not too terrible over five years. But the usual way to evaluate the growth in taxes is to compare them with the size of the economy (measured by nominal GDP) at the time. This is the way the Organisation for Economic Co-operation and Development and many other official bodies do it and was the way the Howard government was happy to have itself measured. It represents a way of assessing the burden of taxation relative to the overall economy's capacity to bear that burden.

Doing it this way shows tax collections have averaged about 21per cent of GDP over Labor's five years. By contrast, they averaged 23.4per cent of GDP over the Libs' 12 years, and a remarkable 24 per cent over their last six years. This is the basis for Swan's claim to be taxing us more lightly than Peter Costello did, and the numbers are on Swan's side. The truth is that Costello was our highest-taxing treasurer ever, although for much of his time he tried to hide the fact by pretending the goods and services tax had nothing to do with the feds. In 2004-05 and 2005-06 tax collection reached a record 24.2per cent.

Of course, although politicians often like to pretend everything that happens in the economy happens because they made it happen, the truth is that much of what happens is caused by factors beyond their control. A big part of the reason the Libs' raised so much tax is that they presided over the first half of the resources boom, before the GFC. And much of the reason Swan has taxed us more lightly is that some taxes haven't fully recovered from the GFC, the second half of the resources boom hasn't been as lucrative as the first, export prices have now fallen back a long way and, to make things worse for the taxman, the fall in export prices hasn't led to a fall in the dollar. Twitter: @1RossGittins