One of the debates that recurs incessantly when researchers discuss scales (we don't get out much) is whether or not your scale needs a midpoint.
The theoretical pros and cons are fairly obvious. If you offer a midpoint then respondents may disproportionately choose it because they're wary of revealing their real view, unsure of what they think, or simply don't care very much. On the other hand, if you don't offer a midpoint you may be forcing customers to go one way or the other when they genuinely feel neutral or unsure.
Yorkshire County Cricket Club recently asked me "Are you likely to attend one of the IT20 matches at Emerald Headingley in 2020?" with the options "Very likely", "Likely", "Unlikely", "Very unlikely". The truth is, I hadn't really thought about it yet, and the answer is something like "maybe, it depends when they are and who's playing."
Which of the responses does that fall into? I suspect they've deliberately excluded the midpoint so that their data is clearly positive or negative; but assuming there are many people as bad at planning as I am, it means that a lot of the mildly positive or negative responses will be essentially random. I'm not sure that's helpful.
It's always a mistake in research to force customers into giving you answers that result in the type of data you want, rather than allowing them to express how they really feel.
So does that mean we always need a midpoint? I don't think so. Our most commonly used scale, for instance, is a 10 point numerical scale from "Completely dissatisfied" to "Completely satisfied". There's no midpoint, but you probably had to think for a bit before you were sure of that. Why? Because it's a very sensitive scale, able to make fine distinctions, so customers can express very mild satisfaction or dissatisfaction. Satisfaction is not something we'd expect someone to feel truly neutral about, but they might not feel able to answer. That's why we always provide a "Not applicable" option.
Don't force customers to answer questions they don't know the answer to, and don't confuse "don't know" with neutral.
So, should you or should you not use a midpoint? Here are some rules of thumb: