A report by a prominent think tank has questioned whether higher health spending in Scotland compared with England has made any difference.
The Centre for Public Policy in the Regions said it was hard to measure the effect of the extra spending.
According to government figures, £200 per head more is spent on health in Scotland than in England.
A Scottish government spokesperson said the report was ill informed and overlooked health factors in Scotland.
The spokesperson added: "Scotland's health is improving but not quickly enough and unacceptable inequalities continue to blight the lives of our most deprived communities. "
The government stressed that NHS Scotland faced "unique challenges in a UK context" particularly around "deep-seated issues of deprivation and ill health and of course our dispersed geography".
The extra cash has traditionally been explained by the different demands of population spread and poverty.
However, when it comes to life expectancy, the report's authors said there was a "mysterious Scottish effect" which went beyond deprivation that made Scots sicker and more likely to die early.
The report comes as figures showed spending on Scotland's health service had doubled in the past decade.
The study by the CPPR and auditors KPMG found that despite improvements in death rates from cancer, heart disease and strokes in Scotland, there had been similar improvements in other countries.
Staffing levels north of the border are also about 30% higher than those in England.
John McLaren, of CPPR, said: "Our research has shown that while health spending and staffing levels per head in Scotland appear to be greater than in England, we are not experiencing the improved health outcomes that might have been hoped would have followed.
"This could be due to worsening needs in Scotland relative to England, for example due to differing behavioural patterns, but at present it is difficult to convert any such higher needs into extra costs."
Jenny Stewart, head of public sector for KPMG in Scotland, said: "We are now spending just short of £2,000 per head per year on the NHS in Scotland - some £212 to £267 per head more than in England.
"Huge improvements have been made in death rates, particularly cancer, heart disease and strokes, but the rate of improvement is no more than other countries.
"Given that funding will become ever tighter - while demand increases - we need to find more innovative ways to secure better health outcomes and focus strongly on productivity."
The report was triggered after a recent Nuffield Trust report on the performance of the NHS across the UK which claimed that Scotland not only had the highest levels of poor health, health expenditure and staffing, but also had the lowest rates of staff productivity.
However, the CPPR said that data problems in relation to staff numbers and activity rates meant that many of the Nuffield Trust's findings were not robust.