Who needs economic modelling when you can go down to the local watering hole and run your brilliant idea past some inebriates propping up the bar?

Treasurer Scott Morrison's parrying of Labor demands that he produce the numbers that spelled out the economic benefit of the Government's tax cuts to small business wasn't elegant.

It didn't pass the smell test, let alone the pub test.

"I tell you what, if you go down the pub and you talk to small business people, they're not talking about econometric models," he told journalists.

"What they're talking about is how they're going to grow their businesses."

There is a good reason why he might not want to release that modelling, if he's got it. It would show that the $24 billion price tag delivers a rather puny dividend.

But growth's growth, they say. And you take it where you can. Or at least when it's convenient.

Think back to last year when the Government looked seriously at increasing the rate of the GST from 10 per cent to 15 per cent.

The proposal, Treasury calculated, would raise an extra $35 billion. This would be ploughed back into personal income tax cuts and increased pension payments.

The "tax switch" would have had a one-off maximum impact on economic growth of 0.3 per cent, according to Treasury analysis.

This was considered a "negligible" increase and the Government binned the idea in February last year.

Here's betting the economic impact of the small business tax cuts is less than 0.3 per cent — a bit inconvenient for a Government whose political ideology reveres the small business above others.

Better then to not go there at all, which is what the Treasurer has effectively been doing by referring to the impact of the Government's 10-year $50 billion tax cut plan which it says would increase GDP by 1 per cent.

Most of this growth would come from the top end of town, assuming the Government landed its plan to cut company tax across the board to 25 per cent.

But shhhh ... the Government doesn't want this said too loudly, if at all.

Because when it comes to corporate tax cuts, political and economic stories take divergent paths — the least popular tax cuts, those that would go to big business, would be most beneficial to the economy.

And the most politically palatable company tax cut — those to small businesses — generates the least benefit.

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Small businesses, those with fewer than 20 employees, account for about 45 per cent of the private sector workforce but generated just 5.2 per cent of the increase in job growth in the five years to June 2015, according to Australian Bureau of Statistics data.

By comparison, large businesses —those with 200 or more employees — account for 32 per cent of the private sector workforce but generated 66 per cent of the increase in job growth for the same period.

Economist Saul Eslake points to these figures when referring to the Coalition's "ritual genuflection" at the altar of small business.

"There is a strong case in economic theory that cutting the corporate tax rate will boost business investment, productivity and hence real wages, in that order," he says.

"But economists have had enormous difficulty establishing that these effects are of any great significance in the real world.

"But what there is absolutely no support for in either theory or evidence is that there are any gains to be had from taxing small business at lower rates than big ones.

"There is no more evidence to support the view that preferentially taxing small business has any positive impact on growth, jobs or innovation than there is evidence for the Immaculate Conception.

"You either believe it as an article of faith or you don't."

Which is not to say you shouldn't cut corporate taxes, just be mindful of anyone who proffers economic balms by pub test.

Are we pricing ourselves out of foreign investment?

And in any case, just how uncompetitive is Australia's tax system?

According to the Treasurer and the Prime Minister we are at risk of pricing ourselves out of foreign investment.

They point to the United States where President Donald Trump has plans to slash company tax to 15 per cent, and Britain where Prime Minister Theresa May says she may go even lower.

But as the Congressional Budget Office (CBO) in Washington DC reported last month, headline tax rates aren't the full story. It compared tax rates from 2012.

Australia's 30 per cent top statutory corporate tax rate ranks in the middle of G20 nations.

Top of the pile is the US which has an average top corporate tax rate of 39.1 per cent and the United Kingdom is fourth-lowest at 24 per cent.

The average corporate tax rate — what companies paid relative to their income — had the US third highest on 29 per cent. Australia was fourth lowest on 17 per cent and the UK lowest on 10.1 per cent.

But on the measure of effective corporate tax rates — the percentage of tax paid on marginal investments once depreciation is taken into account — Australia was 10.4 per cent, much lower than the US, 18.6 per cent, and the UK,18.7 per cent, but higher than Canada, 8.5 per cent.

As the CBO notes, effective corporate tax rates are a better indicator of companies' incentives to invest in particular countries than the headline rate.

The CBO estimated that even after the UK dropped its top tax rate to 20 per cent in 2015, the effective corporate tax rate was 15.7 per cent, still well above Australia's.

The UK may have slashed its top statutory corporate tax rate but it also significantly tightened tax treatment of depreciation.

As a capital intensive economy, Australia can't afford be complacent, but we are not doing that badly either.

Try explaining that at the pub.