The level of accountability of the police in Northern Ireland could be diminished because of changes to how the force measured performance, auditors said.
In a major shift the PSNI decided to stop setting numerical targets because identifying realistic but challenging goals was difficult to achieve, according to a report by auditor and comptroller general Kieran Donnelly.
Instead, the chief constable and senior commanders aimed for the greatest possible reduction in crime or increase in levels of public confidence in policing or detection rates.
Mr Donnelly's report said: "In the absence of target levels I am concerned that the effectiveness of such scrutiny, and thereby accountability, will be diminished."
Accountability is at the heart of new policing arrangements introduced under the Patten reforms, with the cross-party Policing Board, Ombudsman and criminal justice inspectors part of a web of scrutineers.
Tuesday's Audit Office Review of Continuous Improvement Arrangements in Policing considered whether the performance plan for 2012/13 met obligations imposed on the Policing Board and whether proposed performance indicators and standards were reasonable.
The main theme of the 2012-15 policing plan is to increase community confidence in policing by improving how the PSNI delivers its service, its engagement with the community and how it works with other agencies.
A plan specific to last year included 44 performance measures. Only four, on road safety, specified a quantitative total. The remaining 40 referred to an increase or decrease, a major shift in PSNI approach, audit inspectors said.
According to the audit office, the PSNI has said the revision was due to continued difficulty with a "target-driven approach" to planning - it considered that setting realistic but challenging targets is difficult to achieve.
It also said setting numeric targets can in some cases have a detrimental effect on improving performance, particularly when there is a degree of guesswork and involved a small number of cases. Instead, the PSNI said it would aim for the highest reduction/increase possible for measures included in last year's plan. These included improving confidence in policing and reducing levels of crime and anti-social behaviour.
Mr Donnelly said: "While I note PSNI's comments on target setting, I have concerns about their approach. What precisely the 'highest reduction/increase possible' will mean in practice and the basis on which performance will be judged acceptable or otherwise, is not clear."
He added the difficulty of setting numerical targets should not justify not setting any target levels at all.
"Specific targets help to orientate stakeholders (including PSNI) to the level of performance expected," he said.
"They also help to create a clear sense of focus, priority and timeframe."
The accounting expert said the extent to which a target was or was not met should not be the only criterion for judging success or failure.
"Targets act as flags for scrutineers - where a target is substantially exceeded, or where performance is well below expectations, this should lead to closer examination and explanation," he explained.
"In the absence of target levels, I am concerned that the effectiveness of such scrutiny, and thereby accountability, will be diminished."
The report's key recommendations included that the Policing Board and PSNI assess progress in tackling all types of crime each year, rather than just priority areas.
Reviews of progress on other aspects of police work like improving the service to crime victims, providing commentary on variations between targets and achievement and considering trends and performance of similar forces in the UK should be undertaken, the auditor's 30-page report added.
Performance measures should be reintroduced to specify the level of improvement sought and the timeframe within which this is to be achieved.
A PSNI spokeswoman said: "Crime in Northern Ireland is at a 10-year low and confidence in policing at 87% is the highest ever recorded level.
"PSNI will continue to work with the NI Policing Board to develop a robust policing plan and we remain totally committed to ensuring that we deliver a sustainable and professional service which our communities have confidence in."