Much as I greatly admire the writing and analysis of Ian Bell and Iain Macwhirter, their contributions this week appear to be of a piece with a generally selective interpretation of the recent Institute for Fiscal Studies (IFS) document.

The report explains that its contents are, as it were, the beginning of a process and not a definitive conclusion.

One statistic in this document which genuinely staggers in relation to Norway is the gargantuan surplus over annual GDP of 168% maintained by that country, and substantially attributable to the Oil Fund which Alex Salmond proposes to emulate.

The problem is that an independent Scotland would not have remotely as benign a starting point, given the likely share of UK debt we would inherit – and even with a present surplus of revenue over expenditure, the projected £1 billion annual contribution to a Scottish Oil Fund will be difficult to achieve.

Ian Bell failed to mention the working assumption of the Office for Budget Responsibility (OBR) that oil and gas revenues will fall by 80% by 2024 ("Swinney and Darling fight over oil revenue warning", The Herald, November 19). It may be that the OBR has not really sharpened its collective pencil in coming to that figure but, if it is correct, what is a surplus now will require a lot of new revenue streams to continue in the medium term.

Alex Salmond, who is an economist, will probably be proved right over time in saying that $100 per barrel for brent crude is a reasonable working assumption for the future. The problem there is that any future tax regime will require to offset tax against reliefs as oil fields run down and require to be decommissioned. In parallel, there arises the issue of encouraging the exploration of more challenging (and politically sensitive) waters.

One might also ask whether a policy of sucking the North Sea dry at top speed would be in the best strategic interests of an independent Scotland, even if it means less revenue immediately. The construction of a tax regime which achieves the level of revenue allowing us to maintain our services in the face of demographic pressures will clearly be difficult, and cannot be taken as a given.

According to the IFS, the peak of oil and gas revenues came in the mid-1980s. In any view, this was a time when oil was markedly cheaper, to the point that staff in Aberdeen were posting their keys through the building society door in advance of disappearing.

The sensitivity of Aberdeen to oil prices was as marked then as much as it owes its present buoyancy to the currently high values. While the presence of such an economic powerhouse undoubtedly aids GDP growth, I am less certain how that necessarily translates into substantial oil and gas revenues.

It seems to me Iain Macwhirter is telling us what Scotland might have been, had history taken a different turn, rather that giving any definitive pointer to what we might become as an independent state ("Face reality: We could be as prosperous as Norway", The Herald, November 22).

The launch pad to independence now is different to the 1970s, when one might well argue that "we wuz robbed". For one thing, 40 years' worth of reserves have been extracted, and production overall has declined from its peak.

I suspect the IFS will turn over stones that are unacceptable at times to one or other side of the referendum case. I, for one, welcome a contribution that aims to look at the issue in the round.

David W Cobb,

1 Lennox Avenue,

St Ninian's,

Stirling.

Iain AD Mann (Letters, November 21) and Doug Maughan (November 22) have opposing views about the relevance of New Zealand to the Scottish independence argument. As a joint British-New Zealand citizen, may I throw in my four cents' (tuppence) worth?

I walked into the Kaitaia Aero Club in 2010 and the flying instructor, who hadn't seen me for 15 years, made me a cup of tea and asked me to man the phones while he went flying. I subsequently borrowed the club aircraft at one-third of the standard UK price. This speaks less of economics than of a certain state of mind; an openness, a willingness to trust. Private aviation is cheaper in New Zealand because far more people take part. It wouldn't cross the mind of the average punter in the UK to learn to fly; that is something for posh people.

The gap between rich and poor is far narrower in New Zealand than the UK, and therefore there is a greater social cohesion and, in the bad times – witness the Christchurch earthquakes – people really are "in this together". For the man of independent mind, economic viability, for all its importance, is not the critical question.

It would never cross the mind of a New Zealander to go cap in hand to the big neighbour across the Tasman Sea just because times got tough, just as it never crosses the mind of an All Black that he might lose.

That is not to say that close working relationships cannot exist between friendly neighbours. The inception and development of the Australasian College for Emergency Medicine over the past 28 years will never be eclipsed as an example of what men and women of good will can achieve by standing up to the established and fossilised powers of apparently unmovable tradition.

Dr Hamish Maclaren,

1 Grays Loan,

Thornhill,

Stirling.

I am quite sure an independent Scotland can be as successful as New Zealand (Letters, November 21). However, that is no reason to vote Yes at the forthcoming referendum. The comparison should not be with New Zealand, but rather between Scotland as part of the Union and Scotland as an independent country.

If we are going to look at New Zealand as a role model can we hear as to whether or not there is an overwhelming desire for those on the North Island to break away from those on the South Island and vice versa?

Sandy Gemmill,

40 Warriston Gardens,

Edinburgh.

It is obvious that many of the issues arising in the independence debate will remain unresolved at the time the referendum is voted on and that, consequently, the decision people make will depend in large part on which case they decide to be the more believeable.

Given our First Minister's fast-growing reputation as a misleader of men it will be interesting to see how long the Yes campaign takes to reach the conclusion it can no longer afford to be led by Captain McMainwaring.

Ken Nicholson,

3 Letham Court,

Glasgow.