Interpreting more or less likely to vote questions

I really don't like "does X make you more or less likely to vote" questions. On policy questions they are particularly abhorrent as they are used to try and measure salience - or more often, to try and deliberately overstate the salience of an issue. It's inevitably some pressure group, the campaign for ponies or whatever, asking a question saying "If party X offered you a pony would you be more likely to vote for them?". Everyone says yes, as they like free ponies, and you end up with a press release saying that 70% of people will change their vote based on the issue of pony-ownership, and ponies are going to be the key election deciding issue. Sigh.

When it comes to questions about party leadership the question isn't that bad (it's one of the few contexts where I

use that question structure myself) because it isn't normally being used to gauge the salience of party leadership, it's normally being used to see if a leader or potential leader has a positive or negative impact.

There is nothing wrong with a question asking if Jeremy Corbyn has made people more or less likely to vote Labour... but you need to be careful with interpretation. The overall figures will include a big chunk of people saying Corbyn makes them less likely to vote Labour who would never have voted Labour anyway, and a big chunk of existing Labour voters saying Corbyn makes them more likely to vote Labour (it's why when YouGov ask the question we try to encourage those people to say no difference by offering opinions of "No difference, I was/wasn't going to vote X anyway").

The interesting bits are people who DID vote Labour last time, and say they are less likely, and people who voted for parties other than Labour last time and say they are more likely. But even then "more or less likely" is not a particularly high criteria to meet - "less likely" is a long way short of "not going to". So a headline like the Independent's today saying "Corbyn loses fifth of Labour voters", based on 20% of Labour voters agreeing with a statement that with Corbyn as leader they are more likely to vote Tory is over-egging it. Those voters aren't necessarily lost, they may still vote Labour tomorrow, their likelihood of Labour has just dropped to some degree. We'll have to wait for some voting intention polls to see if there has been any substantial net damage to Labour's support.