You may occasionally see claims based on political polls suggesting that "working class" people hold a particular view, or that "middle class" people think something else.

There's always been good reason to be sceptical of these claims: but some new research from YouGov offers more evidence of why you should probably ignore them altogether.

To understand why, a bit of background on what "working class" and "middle class" usually mean in the context of polls.

Pollsters don't actually ask or check whether people are middle class or working class, and they do not technically claim to report figures. Instead, they sort voters into two broad categories: ABC1 and C2DE. These are called the "NRS social grade" and they were invented in the 1950s for use in marketing.

Broadly, people who work in managerial, administrative, professional, or clerical roles – from doctors through to office interns – are in ABC1s. Meanwhile C2DC is made up of all manual workers – of all different skill level, including such different occupations as aeronautical engineers, street sweepers, factory workers, gardeners, and gas technicians.

It is common in political journalist to simplify ABC1 as "middle class" and and C2DE as "working class". If you haven't spotted them already, there are some big reasons to think that a classification system that made sense in the 1950s does not make sense now.

The first alarm bell is that a solid majority of the British population are now in ABC1: 55 per cent, according to the 2016 NRS calculation. C2DEs – which some journalists present as "working class" – are apparently a minority making up just 45 per cent.

This doesn't necessarily mean fewer people are working class: just that the kind of jobs they are doing has changed. Do you work in an office for close to minimum wage? Congratulations, you are middle class, according to people who interpret NRS social grade in this way. Are you earning a £50,000 salary maintaining aeroplane engines? You are a skilled manual worker, therefore in C2DE, and according to some journalists part of a dwindling working class minority. Even if you agree with this contrast, what does looking at the grades meaningfully tell us about the people being polled? The answer is not a lot.

The problem with NRS social grade become even more apparent when you consider the question of age: the C2DE category also includes state pensioners, who are not working at all. Far from asking what people who go out to work every morning are thinking, the views of C2DE are often just a reflection of what older people think. The fact that social change means younger workers are less likely to go into manual jobs than older cohorts exaggerates this effect.

The result is that a person who is retired, draws the state pension, but also owns a portfolio of Buy To Let properties which they rent out to minimum wage office workers would be working class... their tenants are, of course middle class.

As the NRS itself says: "Some people have questioned the relevance of social grade as society becomes more diverse, and targeting more precise. Social grade was never intended to describe every aspect of society. Nor does it describe consumer motivations."

YouGov's latest study, released on Monday, gives us some more hard data that shows the problems with NRS. As an experiment, the pollster asked people whether they identified as working class, middle class, or upper class, then sorted them by NRS grade.

Top 10 marginal seats to watch at the general election Show all 10 1 /10 Top 10 marginal seats to watch at the general election Top 10 marginal seats to watch at the general election North East Fife Currently held by the SNP with a majority of 2 Getty Top 10 marginal seats to watch at the general election Kensington Currently held by Labour with a majority of 20 Getty Top 10 marginal seats to watch at the general election Perth and North Perthshire Currently held by the SNP with a majority of 21 Getty Top 10 marginal seats to watch at the general election Dudley North Currently held by independent, formerly Labour, MP Ian Austin with a majority of 22 LivingInMediocrity Top 10 marginal seats to watch at the general election Newcastle-under-Lyme Currently held by Labour with a majority of 30 Derek Harper Top 10 marginal seats to watch at the general election Southampton Itchen Currently held by the Conservatives with a majority of 31 Rob Candish Top 10 marginal seats to watch at the general election Richmond Park Currently held by the Conservatives with a majority of 45 Robin Webster Top 10 marginal seats to watch at the general election Crewe and Nantwich Currently held by Labour with a majority of 48 Jaggery Top 10 marginal seats to watch at the general election Glasgow South West Currently held by the SNP with a majority of 60 Alec MacKinnon Top 10 marginal seats to watch at the general election Glasgow East Currently held by the SNP with a majority of 75 Christine Johnstone

41 per cent of ABC1s said they were "working class", and 51 per cent said they were "middle class". 66 per cent of C2DE said they were working class, and 25 per cent middle class. So massive chunks of both disagree with the classification they are given. YouGov also found that ABC1s who consider themselves middle class have more similar voting behaviour to C2DEs who consider themselves middle class than they do with ABC1s who identify as working class, and vice vera.

Whether you agree with people's own identification of their class (which has its own obvious problems) or think there us another criteria, NRS social grade is clearly a mess.