The combined wealth of New Zealand’s Rich Listers in 2015 turns out to be $57.4 billion, around $2.4 billion higher than initially estimated and a striking 12 per cent increase on the previous year’s figure.

When the Rich List was announced in July this year, the National Business Review (NBR) put the value of its 184 individuals and families at $55 billion. (The cut-off for inclusion is having a fortune over $50 million.)

But when I tallied up the entries for each individual/family listed on the website (as preparation for some data analysis), the total came to $57.4 billion.

The explanation, kindly provided to me by NBR staff, is that there were a couple of late-breaking big revaluations owing to shifts in the New Zealand dollar and other currencies. (Since many of the Rich List hold part of the fortunes overseas, shifts in exchange rates can make a big difference to their net worth.) These revaluations made it onto the website figures but not the commentary or the print version.

The result of this correction is that the year-on-year rise in the Rich List’s value was 11.7 per cent over 2014’s figure of $51.2 billion. That’s a pretty striking increase at a time when Reserve Bank figures show households have in the last few years reverted to going into debt rather than saving, and probably only people who own houses in desirable parts of Auckland will have seen their wealth increase by anything like 12 per cent.

Some would say that such a big shift in value just because of currency changes points to the inherent inaccuracy of the Rich List’s figures. But I think it just reflects the fact that these wealthy individuals do have huge variations in their net worth, with sums unimaginable to most of us appearing and disappearing in the blink of an eye.

And it’s worth noting that Thomas Piketty, one of the world’s foremost experts on wealth, uses such surveys in his work and believes they help “impose some discipline on public debate”. Certainly the fact that the Rich List’s value has (once adjusted for inflation) risen from $12.6 billion in 1986 to $57.4 billion today is a useful one to know, and gives us a sense of how much fortunes have increased at one end of the scale (even as debt has increased at the other).