"What we do know from an Official Information Act request we made earlier in the year is that between 2002 and 2011, 308,000ha of sheep, beef, dairy and cropping land was approved for sale to overseas applicants.
"Given Beef and Lamb New Zealand's economic service estimates there is 11.25 million hectares of sheep, beef, dairy and cropping land, this works out at 2.7 per cent.
"Yet there are some vital caveats I need to point out, which means the percentages are much higher than reality."
The Overseas Investment Office recorded only approvals yet not every approval resulted in a sale. Even if land was sold to an overseas applicant at the time, Wills asked if they still owned that land today.
"Quite perceivably a foreign owner at the time of purchase could have on-sold that land to a New Zealander," Willis said.
"The OIO would be none the wiser because no approval is needed to sell land back to a Kiwi.
"Then you need to ask if the overseas applicant at the time remains a foreigner today? In my personal experience, most people who move here to farm take Kiwi citizenship or permanent residence.
"Look at the movie director James Cameron's purchase of Wairarapa farmland.
"Even if he becomes a Kiwi, as far as records are concerned he will always be an overseas applicant because that was his status at the time he applied."
These factors meant any percentages people came up with would always inflate reality, Willis said.
"It is also why before any politician tightens the Overseas Investment Act, we need to have a proper census of who owns what," he said.
"We need a datum point first, otherwise we are simply allowing emotion and guesses to dictate discussion and that is the basis for bad public policy."
Donald said Rosenberg appeared to have misunderstood or misinterpreted the figures.
Terralink issued a statement earlier this year which said that for the period from August 25, 2005, to March 13, 2012, 1.44 per cent of New Zealand land designated as rural was given consent by the Overseas Investment Office for foreign ownership, Donald said, taking that starting point because that was when the new act came into force.
Rosenberg said Terralink's low estimate was based on land purchases over the past seven years, so missed any land held before that date.
"And it ignores all the substantial data problems in making such estimates," he said, citing the example of rural land excluding forestry.
"I analysed these matters carefully and concluded the overseas ownership of land was at least 8.7 per cent of farmland, including forestry land, and could well be 10 per cent.
"Terralink's analysis, though being billed as dispelling myths, unfortunately hasn't helped clear the murk.
"Federated Farmers is quite right in asking for good data."
