Last night we got a leaked version of the Labour manifesto. Over the next week it will be joined by the manifestos from all the other parties too. Lots of people will write articles about their impact. We will see polls asking about those policies and whether people approve of them. Lots of people will ask what impact they will have on voting intention or the result. The answer is probably not much. Specific policies make very little difference to voting intention.

This is counter-intuitive to many. Surely in an election on who is going to run the country, what they’ll say they’ll do will matter? One might very well well think it is what elections SHOULD be about. The thing is, it’s not really how people work.

First, most people don’t know what the policies are, so they can’t be influenced by them. One of the most difficult things for people who follow politics closely (which probably includes most people reading this) to grasp is how different they are from the vast majority who don’t pay much attention to politics. For example, in the first few weeks of the campaign Theresa May was the subject of mockery from people who follow politics for continually using the soundbite “strong and stable leadership”. While it sounded absurd to those of us who heard it a thousand times, when YouGov asked a representative sample of the public if they could recall any slogans or messages she had said only 15% remembered it. Most policies make no difference because most people have no knowledge of them.

Even if people were more aware of policies, it’s not really the sort of thing they vote upon. There is a huge body of academic research around elections and voter choice, and the general consensus is that the important factors in deciding how people vote are which party they normally identify with, what their perceptions are of the leaders are and which party they think would most competently handle the big issues of the day.

As human beings we don’t tend to be particularly good judges of what leads to our decisions (we all tend to overestimate how thoughtful and rational we are, when in reality our decisions are normally based on a jumble of bias, instinct and rules-of-thumb, which we rationalise afterwards). However, if you ask voters directly we don’t even think that policies are why we vote the way we do – most people say that it’s the broad values and priorities of a party that matter, or how good their leader is, not the specific policies they offer.

Of course that doesn’t mean policies aren’t part of the mix. When it comes to whether the public think that a party is competent, whether or not they have policies that seem sensible and well-thought through is probably a factor. What sort of policies a party puts forward will make a contribution to what people make of a party’s values and principles. They are not irrelevant, but they are only a small part of a much bigger mix. What this all means is that one can’t look at the popularity of individual policies and conclude a party will gain support. Any party can put together a shopping list of superficially attractive sounding policies – it’s whether collectively those policies, the people putting them forward, the values they represent, how competently they come across, how all these things come together to create a party that people identify with and think would offer a competent government.

In short, in the absence of other other big events in the coming week, don’t be surprised if the polls carried out after the manifestos appear are much the same as the polls carried out before they were published.