The first is "value capture", meaning who derives benefit from an investment? This is relevant to the argument that the money should be spent on schools and hospitals, or, if the funds must come from the sports budget, sprinkled around the state on dressing sheds and suburban ovals.

The students understood that the benefits of spending public money on education can be non-egalitarian, with only the bright kids capturing any value and the less intelligent waiting until they reached school-leaving age.

Spending on stadiums doesn't benefit those not interested in sport or musical shows, but the events they host do produce a return for the owner.

Most stadia are owned by state governments who charge high fees for the hire of the facility. Remember the now-defunct Gold Coast A-League team owned by Clive Palmer, who capped the crowd at the Robina stadium because an increase would trigger additional costs such as attendants and cleaners?

The stadium rental income, together with the tax payable to the government from the services provided by caterers, taxi companies, hotels and restaurants charging fans attending the event all contribute to public coffers.

This is why NSW Sport Minister Stuart Ayres says the revenue from stadiums will pay for future hospitals and schools.

So why doesn't he quantify the benefit? Well, some value captured is notoriously difficult to measure.

Estimations of the value captured by Melbourne's Formula One grand prix have been widely divergent, with low valuations supporting the "ban the vrooms vrooms", while high estimates are used to justify the money spent by the Victorian government supporting the event.

Some value captured is immeasurable. Residents of the Victorian capital call their city "Marvellous Melbourne" because they really believe it. They have, within a couple of tram stops, access to the MCG and its sports museum, the National Tennis Centre, AAMI rectangular stadium, Etihad stadium and the cultural precinct, including the Arts Centre and National Gallery.

These amenities are all part of an interactive whole, a sum far in excess of its parts, "a critical mass of social infrastructure" - another concept easily understood by high school economics students.

Melbourne's efficient public transport system means the negatives - the networking costs such as traffic congestion - are minimised.

This is what former Victorian premier Jeff Kennett meant when he said Melbourne's facilities, "add comfort to the community".

Sydney visitors to the Australian Open in Melbourne will have noted these benefits and will stay in the city's hotels, enjoying the tennis and theatre shows for days, providing revenue for the Victorian government.

Some of this revenue is used to bid for national and international events that Sydney would like to host.

The value captured justifies the subsidy.

Visitors to the Australian Open will wander past the MCG and study the statues of sportsmen, such as fast bowler Dennis Lillee. Now, there's another benefit that can't be quantified. It may have cost $50,000 to erect but how do you measure the benefit to the citizenry?

OK, Melbourne has geographic advantages over Sydney in this respect. the Yarra River, like London's Thames, is not an impediment to the cluster of facilities, unlike Sydney's harbour, which divides the city.

North Shore silvertails will not cross the Harbour Bridge at weekends.

But Homebush, with its ANZ stadium and associated amenities, can eventually become a "critical mass of social infrastructure", particularly with big employers moving there.

The light rail linking Randwick and the SCG and the new Allianz stadium, together with Fox Studios, will make this hub more interactive.

The argument that $2 billion should be sprinkled around Sydney on grassroots facilities reminds some economists of the history of foreign aid in Third World countries.

Who funds the maintenance of the facilities built? China provides the capital to build the power plant but there is no budget to maintain it. Similarly, what revenue is derived from a new suburban dressing shed?

The costs of collection of revenue would probably exceed the value derived.

Compare this to a focused, income-generating asset, such as a stadium that funds its own maintenance costs.

Furthermore, a stadium can be an egalitarian asset, using price discrimination to fill it, with luxury boxes for the rich and low-cost seating for the poor.