My summer was lost in a heap of numbers.

The product is some new analysis which should, in theory, be very useful to the Scottish Government's forthcoming review of student funding. However, some of the findings do not sit comfortably with a central element of the official line. So I am doubtful about how far the evidence will be heard and am wrestling, not for the first time, with the point of it all.

Into this soul searching has lately stepped American economist Paul Romer, with a paper worrying about what happens when "evidence stops being relevant" and loyalty, to an authority figure or a theory, corrodes attachment to truth-seeking.

He reflects on his own experience, where open criticism of collectively-cherished views was perceived as violation of an honour code. In such a world, false facts, wrong predictions and models that don't make sense are shrugged off. Worse still, people standing by did not care enough to challenge obvious errors.

Romer's target is what he calls "post-real" macroeconomics: but he draws parallels with criticisms of string theory, a branch of physics. The argument goes that string theory has suffered from "tremendously self-confident" individuals operating in "an unusually monolithic community" with "a sense of identification akin to a religious faith" and a disregard for the work of those outside the group, creating "a tendency to interpret evidence optimistically, to believe exaggerated statements."

In macro-economics, he is concerned about a growing reliance on what he labels "facts with unknown truth value" (FWUTVs), extra assumptions which need to be plugged into a model to make it work and which may not always be easy to spot.

For Romer this is an argument about science. Politics, he says, is different, being as much about shared values as truth-seeking. That is right, of course: but only up to a point. The current debate about "post-truth" or "post-fact" politics shows many people still believe that there is an important distinction between truth and untruth in political debate.

In the UK this summer, a bus became symbolic of that difference. In the US, there is Trump.

There is no point coming over all pollyanna about truth and evidence in politics and policy-making. Professor Paul Cairney, confronting the messy reality of government, is rightly brisk about scholarly complaints of "policy-based evidence-making", and urges academics to understand how evidence necessarily collides with other considerations. There has never been age in which parties entered government with commitments based largely on objective analysis, or in which politicians did not make questionable claims.

But it is equally complacent to argue that there's nothing here worth discussing. This week, The Economist echoed what's become a common theme, that what marks out the Trump campaign is how truth itself has become "of secondary importance", something given extra traction by familiar concerns: voter anger at elites, fragmented news sources, social media, simplistic approaches to balanced reporting. Like Romer, it urges that "pro-truthers stand and be counted". For others, postmodernism's anti-Enlightenment stance should take some of the blame.

Perhaps Romer's article seems especially pertinent because the highest-profile policy debates, both in the Brexiting UK and in Scotland, are currently concerned more with modelling alternative futures, than with understanding how well existing systems are working. Into these models may be plugged all sorts of Romerish FWUTVs. Facts with unknown truth value (to put it kindly) inform much recent speculation by David Davis.

Similarly, Theresa May's assertion, that we can ignore the overwhelming evidence from existing selective school systems, rests on adding to her model a whopping new FWUTV which will, for the first time in such systems, somehow prevent detriment to the un-selected. Even the Labour leadership battle is partly about modelling electoral success, and the "truth value" of various "facts" in that context.

Here in Scotland, the Common Weal think tank recently announced plans to model an independent Scotland based not on the Scottish Government's GERS figures, the best available data on public spending and revenue raising here, but on "what an independent Scottish Government would want to spend". Perhaps the plan is zero-based budgeting. That's a well-established process, but tough, because it implies willingness to stop doing existing things, as well as doing new ones.

But given the scale of the dislocation between income and spending GERS revealed, Commonweal's phrasing also sounds rather like a model relying on an enormous FWUTV on the other side of the equation - that there will be much more public revenue raised in Scotland than now.

Indeed, some of the wider reaction to the GERs figures suggested that a section of those active in the debate are squarely in Romer's "post-real" camp, for whom what evidence we have here is not simply (and inevitably) imperfect, but has actually become irrelevant. Belief overcomes everything.

Detachment from evidence matters, not because there is some absolute political truth out there, if only we would follow the data. Of course not. But taking evidence seriously helps keep people and systems accountable. When the available evidence is treated as irrelevant, and there's no political damage in making untrue claims, we all lose in the end. Bad decisions are more likely, and poor practice goes more easily unchallenged.

The more that happens, the more it will not matter what your particular politics are: at some point you or someone you care about will suffer. Only the wealthiest, most insulated, can afford not to care, if we develop a political culture indifferent to evidence and truth, however contestable and imperfect.

That so little penalty, and even some reward, currently seems to be attached to telling us only what we want to hear, and filtering out inconvenient facts, may or may not be new. That hardly matters. Romer observes that "in physics as in macroeconomics, disregard for facts has to be understood as a choice."

Most of us can avoid tangling with string theory. But in relation to politics and policy whether to care about evidence, particularly when it cuts across our beliefs, is a choice we all have to make, every day.

Let's choose to care.

Comment by Lucy Hunter Blackburn, a public policy researcher and former senior civil servant at the Scottish Government. Lucy's website is adventuresinevidence.com and you can follow her on Twitter @LucyHunterB.