Corrections Minister Judith Collins has rejected criticism the National-led Government is doing too little to stop inmates reoffending.
In the past year prison numbers have stabilised after years of increases.
The executive director of reform group Rethinking Crime and Punishment, Kim Workman, says the fact that prison numbers are stable has nothing to do with the recidivism rate.
He says over the past five years, the reoffending rate for people released from prison has grown from 55% to 61%.
However the minister, Judith Collins, says that under National, spending on rehabilitating prisoners has about doubled and the number of inmates undertaking drug and alcohol treatement has increased, which appears to be having an effect.
She says the reoffending rate in 2007/2008 was 61% but with a greater emphasis on rehabilitation there are signs now that fewer inmates are re-offending when released from jail.
In the 2009/2010 financial year, she said, Corrections spent $137.5 million on rehabilitation, representing 15% of the department's total budget.
Figures on the Department of Corrections website show the inmate population was 8755 at the end of March - 61 fewer than a year earlier.