The research challenges the assumption that where more private surgery is available, it improves access to public surgery, finding instead that people in those areas with more private surgery had worse access to operations in the public sector.
Co-author Dr Sarah Derrett said of greatest concern was that even for the poorest people in communities access to public surgery was not better in those areas where there was high private surgery provision.
In the case of joint replacements, access for those in the three lowest socioeconomic groups was lowest in areas with high rates of privately funded surgery.
Access to publicly funded joint replacements in 2001-02 for those in the three poorest decile groups was lowest in Auckland (8.1 operations per 10,000) and highest on the West Coast (39.5).
Otago's rate was 13.3, compared with the national rate of 16.1She would like to see much more discussion around the issues of fairness with regard to private and public surgery provision.
Dr Derrett, with co-authors Tui Bevin, Associate Prof Peter Herbison and Prof Charlotte Paul, from the Dunedin School of Medicine, looked at changes in rates of elective surgery over five years, the geographical variation of surgery in the public sector, the contribution of the public and private sectors to equal access, and access according to socioeconomic status.
They used statistics on surgery for hip and knee joint replacement, cataracts and prostatectomy (excluding ACC patients).
While the publicly funded rate for total joint replacements increased between 2003 and 2004, there was no change in the provision of the other types of surgery, despite increases in health spending.
The researchers found access to publicly funded surgery varied widely according to where people lived, variances which were higher than shown in similar studies in England.
This could have been partly because of the small population in some board regions, but even comparing the major boards, rates differed up to two and a-half times.
Dr Derrett said one of the reasons for the low public surgery rates in areas where there were high private rates was workforce limitations. Private hospitals were often using the same staff who worked in the public sector.
The research paper, recently published in the International Journal of Health Planning and Management, also suggested one possible explanation was a conflict of interest for surgeons working in both public and private and that it would be in their interests to limit provision of services in the public sector.
It pointed out that the prioritisation system introduced in 1996 for the allocation of public surgery should have reduced this possibility.
Another explanation offered was that there had been a history of poor public provision historically in some regions, such as Auckland, and private services had grown to fill the gap.
The paper also noted that some areas such as Otago, which continued to provide above the mean rate for public surgery for the conditions studied, were still not able to offer surgery to all those with moderate or severe condition-related problems affecting their quality of life.
