Treasury-funded research conducted by Motu found no statistically significant increasing in hiring by employers following the introduction of the 90-day trial periods in 2009.
Motu Fellow Isabelle Sin said the research used "data from every firm and every person in New Zealand" to assess the law changes' effect.
"The main effect of the policy was a decrease in dismissal costs for firms, while many employees faced increased uncertainty about their job security for three months after being hired," Sin said.
Some industries saw an increase in hiring following the policy change, but Sin said these effects were insignificant.
"This evidence is statistically weak, meaning the findings may be driven by pure chance and may not reflect any real-world effect."
The policy was controversial on its passing, with unions and the Labour Party arguing it would make employment for vulnerable people precarious.
The Government and business lobbyists said the law change would allow employers more willing to take risks in hiring and would increase jobs.
The policy was implemented in selected industries in 2009, then deemed a success and rolled out nationwide in 2011.
Sin said the policy seemed impotent.
"My research shows that the 90-day trial period isn't helping people get jobs. However it doesn't make people less likely to leave secure jobs and doesn't make employment relationships less stable. Overall, my research suggests the 90-day trial isn't doing much at all," she said.
