A quick note on the Individual Electoral Registration vote tonight and what it means, since I fear it will be badly reported elsewhere. As readers may know, electoral registration has now moved over from household registration (where one member of the household filled in a form to register everyone) to individual registration (there is still a household form to sign off for no change, but new registrations need to be done individually). Making it a little harder to register has created a lot of concern about whether it will lead to falling registration, particularly in residential communities like student halls of residence, where in the past the university authority could have registered everyone en masse.

That, however, is for another time. Tonight’s vote isn’t about the principle of individual registration and will make no difference to whether it happens or not. It is on one narrow, but important, part of the transition from household registration to individual registration.

The normal process of electoral registration is – crudely speaking – that once a year there is a canvas of every household, asking people if their details on the electoral register are correct. Local councils will remove entries that are no longer accurate and add on new people. People who don’t reply at all will be badgered with extra letters and knocks on the door, but eventually some people won’t reply. Those people are left on the register for a year, and then if they don’t reply to two canvasses in a row, deleted from the register. People get one year’s grace without being removed.

During the transition process that was different. The annual canvas in 2014 was cancelled for the transition process – people on the old register were matched against government databases, like benefits records, and those who matched were automatically moved across to the new system. Only people who couldn’t be automatically moved across were contacted and required to register on the new system. There was no cleaning of the register though, even if they couldn’t be automatically moved and across and didn’t respond to contacts, people on the old register were kept on the new Dec 2014 register to make sure they didn’t miss out on the general election.

For 2015 the annual canvas was started again, so every household got a letter asking people to confirm their existing details on the register. People who reply were updated (though new people now need to fill in an individual registration) and people who didn’t reply at all were chased. The question to be decided tonight is what to do with people who didn’t reply (or more specifically, people who don’t reply this year and weren’t verified or registered last year either – the year’s grace remains either way).

The legislation setting up individual registration said that people who don’t reply in 2015 should NOT be removed in 2015, but also specifically gave the government the power to change this by statutory instrument and recommence cleaning in 2015 if they preferred. The Electoral Commission recommended the government did not do this, and gave people the extra year’s grace. This is what tonight’s vote is on – are people who weren’t transitioned or re-registered on the new system in 2014 AND did not reply to this year’s electoral canvas left on the register or not?

In May 2015 there were 1.9m people still on the register who hadn’t been registered under the new system. Of course, all of these entries will not be removed, as there has been a full canvas since then and many of them will have replied to this year’s canvas and now be on the new system. It is still likely to be a substantial number. The change only affects people who replied to the electoral canvas at an address in 2013, but have not subsequently replied to electoral registration officers at that address since then, when during that time efforts will have been made to contact them several times for the transition to individual voting and in this year’s annual canvass. They will probably have had to ignore about nine letters reminding them to register. They also need to not be in receipt of benefits at that address and not on other government databases used for data matching, or they would have been automatically registered. In short, a lot of those people probably couldn’t be matched because they don’t live at that address any more, and may or may not be living or registered somewhere else. Finally, it’s worth remembering that people who are left off this December’s register can register to vote up until a couple of weeks before the local/mayoral/police/Scottish/Welsh elections next year.

In terms of the impact on individual voters, I fear there is some hyperbole going on. However, the impact of the vote isn’t just on individual voters, it’s important for another reason – arguably more so. The registers published on the 1st December this year are the ones that will be used for the new boundary review, and the removal of these rolled over names will make a difference. In the twenty council areas with the highest number of people held over from the 2013 register, about 11% of people on the register in May 2015 were held over, in the twenty council areas with the lowest number of people rolled over about 1% of people on the register in May 2015 were held over. The places with lots of held over entries are mostly (but not exclusively) Labour held areas, the places with few held over entries are mostly (but not exclusively) Conservative held areas. Again, remember many of these people will probably have been picked up in this year’s canvas, so it doesn’t mean 11% and 1% will be removed – the numbers will be lower than that – but it does mean the number of people on the registers will drop more in Labour areas than in Conservative areas.

Cleaning people who have not responded to the canvas off the register will decrease the registered electorate in inner-city Labour areas and make the boundary review better for the Conservatives. Leaving them on will make the boundary review better for Labour. We don’t know what proportion of the rolled over entries on the register relate to real people still living at those addresses and what proportion are “dead entries” related to people who no longer live at that address. The Conservatives can argue that leaving inaccurate entries on the register would skew the review by bumping up the electorate in areas with inaccurate registers full of outdated entries, Labour can argue that harshly pruning the register would skew the review by under-representing the electorate in areas of social-deprivation with populations who are less likely to register to vote. I suspect neither are entirely free from self-interest, but one way or the other it has to be decided: Parliament has until Monday to annul the statutory instrument or it remains law.

Back in 2012 I wrote about the Observer reporting an open-access poll on a website campaigning against the government’s health bill as if it was representative of members of the Royal College of Physicians. I also wrote to the Observer’s readers’ editor, Stephen Pritchard, who wrote this article about it.

The Guardian today is making the same error – they have an article claiming that seven out of ten junior doctors will leave the profession if the new junior doctor’s contract goes through. The headline presents it as representative of all junior doctors and it is referred to as a poll and a survey in the first two paragraphs. Only in the final, seventeenth paragraph is it revealed that it wasn’t conducted by any reputable market research organisation, but a self conducted survey of members of a Facebook group, the Junior Doctors Contract Forum, which is campaigning against the new contract (the Telegraph had a similar article earlier this month that appears to be based on the same data).

We cannot tell if efforts were made to limit the poll to actual doctors or to make it representative of junior doctors in terms of career stage, age, region and so on – it doesn’t really matter, as it is fatally undermined by being conducted in a forum campaigning against a contract. It would be like conducting a poll on fox hunting in the Countryside Alliance’s Facebook group and presenting that as representative of the countryside’s views on foxhunting. The flaw should be screamingly obvious.

Questions along the lines of “If thing you oppose happens, will you do x?” are extremely dubious anyway. The problem is that respondents to opinion polls are not lab rats, they are human beings who seek to use polls to express their opinion, even when it’s not exactly what the question asks. From a respondent’s point of view, if you are filling in a survey about something you oppose, you’re are likely to give the answers that most effectively express your opposition. Faced with a question like this, it’s far more effective to say you might leave your job if your contract is changed than say you’d meekly accept it and carry on as usual.

We see this again and again in polls seeking to measure the impact of policies. For example, before tuition fees were increased there were lots of polls claiming to show how many young people would be put off going to university by increased fees (such as here and here). After the rise, they miraculously continued to apply anyway. Nobody wants to tell a pollster that they would just swallow the thing they oppose.

I don’t doubt that many or most junior doctors are unhappy with the new contract, but you can’t get a representative poll by surveying campaigning groups, and you shouldn’t necessarily believe people telling pollsters about the awful consequences that will happen if something they don’t like happens. It’s a lot easier to make a threat to a pollster that you’ll resign from your job than it is to actually do it.

UPDATE: While I’m here in voodoo polling corner, I should also highlight this cracking example of a voodoo poll in the Daily Mail. It claims “One in three women admit they watch porn at least once a week”… but it seems to be an open access poll of Marie Claire readers, certainly it is in no way representative of all women in terms of things like age. It contains the delightful line that “Out of the more than 3,000 women surveyed, 91 per cent of the survey’s respondents identify as female, eight per cent identify as men and one per cent is transgender.” I don’t know how to break it to them, but you probably can’t include the 8% who are men in a survey of 3000 women.