The performance gap between the NHS in England and the rest of the UK has narrowed in recent years, despite considerable differences in policy in each country, a wide-ranging report found.
The joint study by the Nuffield Trust and the Health Foundation revealed that England performs marginally better across a number of factors, including amenable mortality rates, life expectancy and ambulance response times.
Scotland saw improvement in terms of sanctions and targets, while Wales saw waiting times for procedures such as knee or hip operations rise sharply since 2010.
In 2012/13 a patient in Wales waited about 170 days for a hip or knee replacement, compared to about 70 days in England and Scotland.
Northern Ireland was found to have improved on many indicators, although MRSA rates remain higher than both England and Wales.
The report analysed 22 indicators, comparing performance of the four UK health systems over the past two decades.
The three-year study assessed the performance of the NHS on the quality of patient care in all four UK countries since devolution.
It found "significant improvements" in the performance of the health service in each country.
But researchers found the gap had narrowed on many indicators, and that differences between health services in England, Scotland Wales and Northern Ireland are often small.
No one country was consistently ahead of the others, despite policy differences such as greater emphasis on patient choice and the use of private sector providers in England, and the rejection of competition in Northern Ireland, Scotland and Wales.
All four countries were found to have substantially increased investment, doubling the amount spent on health care across the UK between 2000/1 and 2012/13, and investing in more staff.
But spending decisions have been markedly different, with Scotland spending almost £900 million of money notionally available for health on other services or making existing services free of charge, such as personal care for older people.
Wales also spent around £450 million on other services.
However, austerity measures have caused a slowing of spending across the board. From 2010/11 to 2012/13 growth in Northern Ireland was 2%, 1% in England and Scotland and a reduction of 1% in Wales.
Since a previous study in 2010, which used data up to 2006/7, nursing staff levels have been lower in England than in the other three countries.
Scotland has improved in terms of targets and performance management, such as ambulance response times and waiting times for planned surgery, which are now similar to England's.
The report also analysed the north east of England in comparison to the four countries, as it shares characteristics with them.
It found the North East has seen higher investment that average for England, of £2,150 per person in 2012/13 compared to £2,114 in Scotland, compared to the English average of £1,912.
The region also experienced marked improvements during the 2000s in treatment rates, hospital staffing, mortality rates and life expectancy.
Dr Jennifer Dixon, chief executive of the Health Foundation, said: "It is very good news for the public that the quality of health care is improving across the UK.
"But what is also humbling for politicians is that so far no one policy cocktail seems to be more effective than another on NHS performance.
"This is despite all the rhetoric about the benefits or otherwise of introducing competition among providers. Clear targets and effective performance management can produce results, for instance, reducing waiting times, but we do know that this regime will only work in a small number of areas of performance. "
Andy McKeon, senior policy fellow at the Nuffield Trust, added: "Our study period coincided with the biggest sustained injection of cash the four health systems have ever seen, so it's perhaps unsurprising that staff numbers have increased and performance has improved.
"But what is interesting is that, despite hotly contested policy differences in structure, targets, competition, patient choice and the use of non-NHS providers, no one country is emerging as a consistent front-runner on health system performance."
He added: "Only time will tell if the four countries' progress made to date will be sustained as austerity starts to bite.
"But Wales's lengthening waiting times should set alarm bells ringing amongst policy makers when considering its possible impacts."