Once we’ve identified a specific construct of interest, the question becomes; ‘how many scale points?’ There’s an easy way to decide. All constructs are either bipolar or unipolar and the number of scale points we assign to a question depends on whether its hidden construct is bipolar or unipolar. Bipolar constructs are those where attitudes can fall on one side or the other of a midpoint that itself is true ambivalence or neutrality. For example, a school principal might want to know if parents think the school day is too long, too short, or just fine. Length, then, is a bipolar construct.
Unipolar constructs are those that lend themselves strictly to an amount–either there is the maximum amount of the attitude or none of it. For instance, let’s say I asked you to rate how helpful this article is. It may fall between being the most helpful article you’ve ever read and not helpful at all. From there, we can safely assume there is something in between–like “sort of” helpful.
So far that’s three response options that we can easily wrap our minds around. After that a response option in between the midpoint and the anchors is about all our brains can handle. Thus we are left with: Extremely helpful, Very helpful, Somewhat helpful, Slightly helpful, Not at all helpful–five scale points. While there is a “middle” point, the expression of that point is decidedly not synonymous with “neutral.”
Bipolar scales require seven scale points, three around each side of the midpoint–again a midpoint that truly means neutral, neither, or both. If we go back to our school principal example, she would ask if the school day was: Much too long, Somewhat too long, A little too long, About right, A little too short, Somewhat too short, Much too short.
There has long been a ton of debate and confusion about scale point numbering. The academic scholarship has demonstrated that scales are most reliable when constructed with five and seven scale points.