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The review of the four UK health systems by the Nuffield Trust and Health Foundation has been a painstaking piece of work.

Researchers have been working on it for the best part of four years, grappling with different data sets on topics as diverse as spending, waiting times and death rates.

But it is perhaps the questions the report poses rather than the ones it answers that provide most food for thought.

Post devolution, the UK has three distinctive systems.

In England, there is a great deal of emphasis on competition (both between NHS bodies themselves and with the private sector).

By contrast, in Scotland and Wales collaboration is key; and in Northern Ireland there is an integrated approach where health and social care are part of the same system.

Burden of ill health

It should provide a perfect platform from which to assess the merits of each approach.

Except it doesn't. Performance on a whole host of measures is remarkably similar - or where there are differences there are obvious answers.

For example, the slower adoption of targets outside England can explain some of the gap on waiting times, while the higher burden of ill health is the main reason that Scotland lags behind on measures such as life expectancy and death rates.

These factors can also give an answer to why Scotland, Wales and Northern Ireland appear to be catching up with England on some measures - it is easier to make faster progress from a lower base.

But all this just raises the question: what actually does influence performance?

Funding was the obvious answers proposed by researchers.

However, the report also throws up some other, interesting theories.

Local data was provided for one region - the North East of England. This was chosen because in terms of population demographics and health profile it was considered to be the closest fit to Wales and Scotland.

The findings were fascinating. In the early 1990s death rates and life expectancy were similar to Scotland, but now the North East is outperforming it by 15% to 19% on death rates and a year of life expectancy.

So what has happened? Well, it wasn't the impact of competition within the NHS, which is much less frequently used in the North East than elsewhere in England.

Instead, study leader Prof Nick Mays suggested it could be linked to the lack of high-paid jobs in other professions, which allows the NHS to recruit and retain the most talented staff.

It is not the first time this point has been made. The Centre for Economic Performance also noted the correlation in .

If that is the case, it raises two interesting points.

First - unsurprisingly - money matters when it comes to attracting the best staff.

But second, what happens locally (and it would be fair to assume this could apply to a host of other factors) is perhaps more important than the national levers that politicians pull.

So instead of looking at performance across countries, it might be better to think of the NHS as a collection of many different systems.