Wait times dropped after emergency department time targets were introduced but a report has found some hospitals shuffled patients around just to meet the target.

A University of Auckland-led study published in BioMed Central Health Services Research studied emergency department (ED) waiting times at four New Zealand hospitals between 2006 and 2012.

With hospitals under pressure, a target measure was introduced in an effort to minimise crowding, which left some patients in hospital corridors.

Official DHB reports found most EDs met the 95 per cent target to be seen, treated or discharged within six hours. However, the introduction of "short-stay units" in the last 10-years has seen researchers question those reports.

Hospitals record the length of stay in EDs, but shifting patients into the short-stay units isn't counted in reported ED figures.

The reported and total ED length of stay figures showed a reduction in the first 18 months of the target introduction from 2009. Reported ED length of stay continued to improve after 2010, but total ED length of stay figures remained static.

The findings suggested hospitals were moving patients into the short-stay units in part just to meet target performance.

Associate Professor of the University of Auckland's School of Population Health Dr Tim Tenbensel said moving patients to the short-stay-units was reasonable in most cases.

However, their interviews confirmed there were other instances in which patients were moved solely to meet the target requirement.

"Having patients in these short-stay units is certainly preferable to having them wait in hospital corridors as was common before 2009.

"However, we know from our interviews that there were some instances where the only reason patients were transferred to short-stay was to avoid breaching the target."

While the introduction of the ED target was initially successful, Tenbensel said the official DBH reports did not accurately represent patient stay times.

"The increasing use of short-stay units means that time spent waiting in ED is becoming less useful as a way of measuring hospitals' responses to demand for acute services," he said.

"Without including short-stay unit waiting times, we don't get the full picture. Our analysis questions the value of ED targets as a long term approach. To the extent that ED targets work in improving timeliness of care, it is in the form of a short, sharp shock.

"Given that ED demand continues to increase at rates above population growth rates and increases in health sector funding, additional policy and organisational strategies will be required in order to meet the challenges of increasing acute demand."

Two of the four studied hospitals were in larger urban areas, while the other two were in a regional centre and in a provincial city.

The study found streamlining ED waiting times was most effective. A 3-2-1 approach, which sees a 3-hour ED assessment phase, followed by a 2-hour inpatient assessment phase and a 1-hour transfer ward phase worked well.

Moving patients to the short-stay-units allowed movement of other patients within the hospital. All four hospitals reworked their medical rosters to cope with the increased patient demand.

Further initiatives like increasing staff resources only began in 2010, so were not found to reduce total length of stay.

"It appears that the effectiveness of the target in reducing patient time in EDs was confined to the period from mid-2009 to late 2010.

"From 2011 onwards, improved target performance was achieved by increasing use of short-stay units as a tool for managing acute hospital demand.

"This means that the continued improvement of DHBs in official ED target performance after 2010 does not give the full picture."