I just had a question on Google+ that I thought I would also post here:
So….what IS unipolar (defined) and when would I ever use it?
Thanks for the question: Unipolar scales measure an attribute across one dimension. For example let’s use hunger: not at all hungry, slightly hungry, moderately hungry, very hungry, extremely hungry.
You could also look at it like it’s going from 0 in intensity up to a 4 in intensity.
|Hunger unipolar scale|
|Not at all hungry||Slightly hungry||Moderately hungry||Very hungry||Extremely hungry|
A bipolar scale is using two opposite dimensions. It’s inferring there are dimensions within the 0. If you’re not hungry, is it because you’re so full you could burst or is it because you ate two walnuts and feel like you could wait another hour to eat?
The bipolar scale measures the full side and the hungry side. For example: extremely satiated, somewhat satiated, content, somewhat hungry, extremely hungry. This scale is moving more like -2 -1 0 1 2.
|Hunger bipolar scale|
|Extremely satiated||Somewhat satiated||Content||Somewhat hungry||Extremely hungry|
So when would you use one over the other?
That is a question for which every survey writer will likely have a different answer. It’s all about the circumstance and what you are trying to measure.
If you are measuring a person who just came into a restaurant because you want to know how large of a portion to feed them, you may want to use the unipolar scale. You get more granularity within the hungry side of things and you might assume that they showed up at the restaurant without having eaten something beforehand so there would be few satiated people upon arrival.
If you are measuring a person who is just leaving your restaurant after you fed them a meal, and you only have these two scales to choose from, you may want to use the bipolar scale in order to find out if they are leaving still hungry or at a comfortable satiation point. Or you could make a separate unipolar scale based on the “full” aspect. Are they going to run out and get dessert somewhere else or are they going home to moan on the coach?
I hope this helps.