Why use survey scales?
Survey scales are important because they help respondents quantify what they think or how they feel about certain things. In other words, they allow respondents to assign specific quantifiable values to feelings, ideas, experiences, and expectations instead of providing vague or ambiguous responses.
Choosing the number of rating levels
After you decide what you want respondents to rate (i.e., liking, agreement, etc.), you need to determine how many rating levels they’ll be able to choose from. How fine of a distinction do you want to be able to make between those who agree or those who disagree? Decades of psychological research have shown that a six-point scale with three levels of disagreement and three levels of agreement works best. Here’s an example:
Avoiding response bias
A six-point scale gives you ample flexibility for data analysis. Depending on the questions, other scales may be appropriate — but the important thing to remember is that it must be balanced, or you will build in response bias. For example, a recent survey of the U.S. Post Office conducted by a household name survey company included the following scale:
Stay away from neutral ratings
Surveys created by trained researchers will not contain a neutral option, such as “I don’t know,” in the scale. Including a neutral rating option negatively influences your data, which can have a huge impact on your survey results.
People harbor opinions about virtually everything, including things on which they think they have no opinion. The president of an East Coast survey consulting firm suggested that we consider “vanilla ice cream” as an example in defense of the firm’s use of a neutral point. He expected us to be neutral about it — but we were not. We said we liked vanilla ice cream.
When people are encouraged to make a selection one way or the other — whether it is like/dislike or agree/disagree — they can do so, even if they lean that way slightly. Providing a “no-brain” option allows them an escape from thinking about an answer, and it costs you data.
“I don’t know” costs you money
There is also a financial reason for not having a neutral point in your survey scale. Here is a common five-point scale: