Mr Forster is concerned there is a "real risk" the Government has not been "accurately or effectively briefed" by ACC, because of issues with some of the statistics used.
He was the lead author of an independent report, released last month and titled "Solving the Problem", which suggested establishing a commissioner for personal injury at ACC to improve transparency, and access to justice.
Backed by a $150,000 grant from the New Zealand Law Foundation, Mr Forster had since compared statistics on the number of claims ACC said it declined, as given by ACC to various agencies, and found "clear contradictions".
"It appears that ACC is giving different numbers to different agencies," he said.
When the Otago report was released, ACC said in a statement that it had advised an ACC review undertaken by Miriam Dean QC last year that ACC made "70,0000 decisions declining cover or entitlements", based on 2012 figures, and that about 6500 reviews of ACC decisions were sought by claimants annually.
By contrast, ACC-supplied figures included in a just-released Ministry for Business, Innovation and Employment report, and covering the 12 months to February this year, suggested that 1,861,180 ACC claims were accepted, 43,914 declined, and only 1469 reviews sought and filed over that time.
Mr Forster was "disturbed" by both sets of figures.
"ACC’s own recent public statements indicate the figure was 70,000, so a figure of only 43,914 to MBIE simply cannot be correct," he said.
In any case, extensive research had been undertaken for the university report, based on ACC figures obtained under the Official Information Act.
And he stood by the report’s estimate that the full annual figure for declined ACC claims was likely to be between 200,000 and 300,000.
Statistics were crucial to understanding access to justice issues within ACC, and sound decision-making needed to be based on clear and accurate information.
Continuing issues with inadequate transparency showed "why we need a commissioner" to provide further oversight and co-ordination at ACC.
The Otago report’s researchers had offered their help to ACC. Approached for comment over Mr Forster’s concerns, an ACC spokesman said he understood "ACC will be touching base with Mr Forster directly to offer to arrange further meetings with him".
"ACC stands by its data but is interested to understand how Mr Forster arrived at some of his estimates."
Mr Forster had quoted ACC statistics "covering different time periods" and had "drawn conclusions" from data that was "not comparable", the spokesman said.
