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Political parties are generally in agreement about one thing - that the NHS needs more money. But is money all it takes?

To answer this, it's helpful to look at whether the NHS is getting the best out of its existing budget - and how that compares with other countries.

Value for money

There's no single way of measuring the efficiency of a health service, though various bodies have tried.

Bloomberg's annual healthcare efficiency index, for example, looks simply at spending on healthcare versus life expectancy.

Its latest report ranked 56 wealthy countries, based on 2015 data. It put the UK 35th - down from 21st the year before, partly reflecting the slowing of growth in spending on the NHS particularly in England.

Hong Kong and Singapore - mixed public and private systems with elements of both government funding and insurance - came top. They were followed by Italy and Spain - with national health services - which both have higher life expectancies than the UK and spend less per person to achieve this.

The UK was also beaten by France which has a system of social insurance paid for by the government, individuals and employers.

Compared with 35 other OECD countries (Organisation of Economic Cooperation and Development) - a group of rich nations - the UK spends an average amount on healthcare (about 9.8% of GDP) and has a slightly higher than average life expectancy for the group (81.3 years).

Is life expectancy a good measure?

Life expectancy is a reasonable proxy for how good a healthcare system is, but it's not a perfect one.

While higher healthcare spending is linked to higher life expectancy, it's affected by other complicated social factors including diet and smoking. In the US, for example, opioid deaths and gun crime have been linked to a fall in life expectancy.

It's also a fairly crude measure - living longer isn't the only thing most people would want to achieve from a health system.

As a 2018 report by three health think tanks and the Institute for Fiscal Studies, entitled "How good is the NHS?", said, UK patients were more likely than average to report having had a good experience of the health system. The think tanks said this was "a valuable goal of health care in its own right".

UK patients were also less likely to say they skipped a consultation or prescription medicine because of cost.

And looking just at life expectancy doesn't capture how good a health system is at dealing with conditions that may require long-term care but don't cause death.

The 2018 report concludes that the NHS across the UK is relatively efficient, performing well in managing long-term conditions with "an unusually low level of staffing and, in at least some categories, equipment" compared with other countries. This suggests the NHS is doing quite well with the money it has.

But equally, life expectancy measures don't capture experiences like waiting for a long time on a trolley in A&E or waiting in pain for a routine operation, which aren't fatal but are also not good experiences for patients.

These have worsened as funding increases have slowed.

How good are health outcomes?

The NHS is below average among OECD countries at treating the illnesses that are the most common direct causes of death.

For example, the UK mortality rate for cancer and heart disease is higher than the average among similar countries and that's a longer-term trend.

Part of the reason the UK does worse on cancer survival is that British patients present late with cancer symptoms, and get diagnosed at a later stage. That's not necessarily a funding issue.

Across the UK, waiting times for routine surgery like hip replacements are about average, and waiting times in A&E just below average, compared with other rich countries.

A&E performance across UK % of patients dealt with inside four hours

As the growth in funding has slowed, though, the NHS has become worse at seeing people within four hours in A&E and getting cancer patients into treatment within two months.

This is significant for patients and their experience of the system, but it hasn't dramatically effected outcomes - although this may take some time to show up. Those worse than average trends pre-dated recent funding cutbacks, again suggesting there's something other than just money going on.

Improving outcomes in the health service often requires funding plus other action - for example training and retaining more staff or launching public information campaigns. Money alone is not enough to make those things happen.

The NHS is devolved, meaning each nation runs its own health system and can set its own priorities. On waits in A&E, Scotland has fared comparatively better than other UK nations.

Equal access

US-based foundation the Commonwealth Fund published a comparison in 2017 which put the UK top out of 11 countries for healthcare performance.

It looked at five areas including equity and access, as well as health outcomes and the care process.

The UK came top partly because of the ranking's heavy weighting towards universal systems - since equity and access formed two out of the five criteria.

When it came to health outcomes, though, the UK scored tenth out of 11 countries which detracts from the overall score.

Although, arguably, the UK's relative equality of access to healthcare for both the rich and poor is a significant when it comes to assessing how well the health service is spending its money.

So what's the verdict?

The IFS, Health Foundation, King's Fund and Nuffield Trust say the NHS "does better than health systems in comparable countries at protecting people from heavy financial costs when they are ill" and that overall, "the NHS performs neither as well as its supporters sometimes claim nor as badly as its critics often allege."