The Greens have accused Prime Minister John Key of massaging figures to hide the number of ACC decisions being overturned falling below the Government's own target.

The Greens yesterday questioned whether a rising number of overturned decisions proved legitimate claimants were missing out on compensation they were entitled to.

Key yesterday told Parliament "over the past six years the average percentage of disputed decisions found in the corporation's favour is 71.8 per cent".

Claims that "because a few cases go against the Corporation, everything is broken there, is just simply incorrect", he said.

However, the Greens' ACC spokesman Kevin Hague has released figures showing the number of ACC decisions being upheld by the Dispute Resolution Service had been steadily falling from 76.8 per cent in 2009 to 55.8 per cent in the 2012 year-to-date.

"Over the past couple of years ACC has failed to meet the 70 per cent target for decisions upheld."

The "extremely generous" target was set by the Government itself, he said.

"Anytime you have the Prime Minister giving an average over years under his government and years under the previous government, it pays to look further."

Of the 55.8 per cent of decisions upheld, some of those would also be overturned, Hague said.

"Some proportion of those claimants that lose disputes will have the fortitude to go further and appeal to the district court where roughly half of them are being overturned."

But the majority of people who had ACC decisions go against them, wouldn't take if further, he said. That applied particularly to Maori and Pacific Islanders who tend to be manual workers and often didn't understand their rights of appeal.

"My belief is that ACC relies on that in quite a cynical way."

Meanwhile, ACC Minister Judith Collins is expected to today announce a new three-year contact between the Corporation and the Government.

Collins has said she wants to drive a "culture change" to restore public confidence in ACC after the Bronwyn Pullar saga and massive privacy breach led to the resignations of former ACC minister Nick Smith, board chair John Judge, chief executive Ralph Stewart and three other board members.

Fairfax Media revealed this month that ACC had been targeting what it called "low hanging fruit" and had slashed the number of long-term claimants from about 13,500 to 10,935 since 2009.

ACC DECISIONS UPHELD ON REVIEW BY THE DISPUTE RESOLUTION SERVICE:

2007 - 72.9

2008 - 74.4

2009 - 76.8

2010 - 64.7

2011 - 66.2

YTD 2012 - 55.8

- © Fairfax NZ News