A poll in the Independent shows that voters think Theresa May and the Tories would do a better job than Jeremy Corbyn of managing the NHS. Which poses the question: how can Labour be so weak on what should be its core strength?

Let's start with the statistics. Since 2010, real spending per person on the NHS has grown by just 1.3% per year. That compares to growth of 6.3% per year under the 1997-2010 New Labour government. This relative squeeze means that, as Simon Stevens says, there are "clearly substantial funding pressures" on the NHS. It's surely plausible that, in the absence of policies to greatly improve efficiency, this reduced spending growth might have contributed to the "humanitarian crisis" in the NHS.

Why, then, isn't the government being blamed more?

One reason is that these statistics aren't sufficiently well known. They're quite hard to find: I got them from publicspending.co.uk. One reason why they're not is lies with the atrocious standard of political reporting. This usually consists of "he says, she says" claim and counter-claim in which clear facts and ground truth are effaced.

The result of this is that austerity has been presented as an abstract concept which is a matter of debate within the Westminster bubble rather than what it is - an act of vandalism which does real harm to real people. Closures of Sure Start centres, prison riots, bad social care, benefit sanctions, flooding and now a malfunctioning NHS are all seen as separate issues rather than what they are - the real human damage of macroeconomic policy.

Stalin once said that "if only one man dies of hunger, that is a tragedy. If millions die, that's only statistics." The Tories are pulling off a similar trick.

But there's something else - the halo effect. Traditionally, Hollywood heroes have been not just better-looking than villains but more charming, smarter and better shots too. This reflects our tendency to assume that if someone has one good quality they must have others. The fact that the Tories are popular for other reasons thus spills over into a belief in their competence even in an area where it is not deserved.

This is magnified by three other tendencies. One is simple deference. As Adam Smith said, we have "a disposition to admire, and almost to worship, the rich and the powerful". A lot of the routine rituals of government exploit this disposition by enhancing what Rodney Barker has called legitimating identities: apparently minor matters such as pictures of Ms May getting out of chauffeured cars, greeting foreign leaders, speaking at a podium with the media a respectful distance away and having speeches trailed as big set-pieces all serve to enhance the appearance of authority.

A second is a trick of Ms May. In being quiet and boring she has allowed the media to assume that she must at least be competent; in this way, she managed to avoid getting blamed personally for the government's failure to hit its immigration targets despite being Home Secretary.

Thirdly, though, Labour is itself partly to blame. Legitimation rituals and the halo effect work in both directions. If you don't obey the Westminster rules of politics - for example if you speak at rallies rather than do the standard media rounds - you'll not be spoken of as a "credible" leader. And if you are incompetent in some respects, you'll be thought incompetent in others. Voters might well ask: "If Corbyn can't manage the Labour party, how can he manage the NHS?" Whether the blame for this lies with the media, recalcitrant MPs or Corbyn himself is of course a matter of debate. In this debate, however, facts can be ignored.