Not everything that stinks causes disease. Yes, there is plenty wrong with the press and BBC, but how much influence does it actually have?

I ask because of Simon's recent post blaming the media for the sheer incompetence of this government. I'm not so sure about this. The press has always had a right-wing bias, but we haven't always had a government as lousy as this one. This alone tells us that other factors are at work: mechanisms that select for fanatics and against competence have strengthened in recent years.

Equally, it would be stretching things to blame the media for the rise of coarse right-wing populism. The press has been fomenting this for decades: the Sun ran the headline "Up Yours, Delors" way back in 1990. But it is only in recent years that it has become so widespread. This tells us to look elsewhere for explanations - for example in increased (perceived) threats to old white male supremacy or to the psychological impact of economic stagnation. As Martin Wolf says, "sharing out losses generated by a financial crisis, followed by the inevitably weak recovery, always creates public rage."

What's more, the cognitive biases research inspired by Kahneman and Tversky shows us that people are perfectly able to be idiots without reading the papers. Pro-capitalist ideology can emerge without their help.

And personally, I find blaming the press to be aesthetically displeasing: I fear it can sometimes come close to conspiracy theory, and under-rates the importance of emergence.

We also have empirical evidence from the US that the press doesn't much matter. Matthew Gentzkow and colleagues used the opening and closing of daily newspapers to estimate effects on voting behaviour and found (pdf) "no evidence that partisan newspapers affect party vote shares." One reason for this is that papers respond to readers' ideologies (pdf), not vice versa.

But, but, but. There's also evidence on the other side. Jonathan McDonald Ladd and Gabriel Lenz show that Sun readers were more likely (pdf) to vote Labour in 1997 than otherwise similar people who didn't read the rag, implying that the Sun's shift to supporting Labour in the 1997 election did shift votes. US evidence shows that the roll-out of Fox News boosted the Republican vote. One study has found (pdf) "quantitative and qualitative evidence that media coverage may have played a unique causal role in increasing support for UKIP," And the fact that young people are far more left-wing than oldsters - something which was not the case in the 80s - might be due in part to the fact that they don't read the papers.

What's more important for me, though, is perhaps the role of the press in shaping the agenda, in deciding what gets talked about: in this context is the constant drip, drip of stories that matters more than any individual one. Simon is right to say that media stories of Labour's over-spending created a climate receptive to Tory claims that government borrowing was a big problem. The MPs' expenses "scandal" helped to foster a distrust of parliamentarians*. And anti-immigrant stories in the papers might well help explain the otherwise curious fact that anti-migrant sentiment tends to be strongest in areas which have low immigration. When people can compare the evidence of their own eyes to newspaper stories, they disbelieve the latter, but when they can't...

Of course, if the press puts some things onto the agenda it follows that others things are kept off it. Not least of these is the truth. The fact that people were ignorant of basic facts about the EU in 2016 and that Tory MPs needed a training session this year on what a customs union is both tell us that the media does a lousy job of informing people.

The facts, though, aren't the only things avoided. In talking about Brexit, immigration, identity politics and so on, important questions get ignored - such as the causes of stagnant real wages or of inequality. Even well-meaning journalists, in their search for heroes and villains, tend to under-rate the importance of emergent social phenomena. One of the BBC's greatest failings is perhaps a tendency to take its agenda from the press, thereby exacerbating the bias against understanding.

Net, then, I suspect our media is indeed a problem, though not the only one. Which means that one task of the left - a task it has for years failed at - is to change what we talk about.

* The fact that some of the most imaginative writing in English literature has sometimes been in journalists' own expenses claims was curiously overlooked in that affair.