A constant sum scale is a type of question used in a market research survey in which respondents are required to divide a specific number of points or percent’s as part of a total sum. The allocation of points are divided to detail the variance and weight of each category.
Constant sum scales are a less frequently used question in surveys when compared to basic likert scales, single radio responses, or checklists (i.e. multiple response options). They are an excellent way to create variance among a data set and truly understand which factors are key and which are not for customers or respondents.
They are especially helpful if you need to ask a question to a customer or respondent where you believe several factors are critical or of high importance. You are more likely to create differentiation in the data with a constant sum when compared to other question types.
Example of a Constant Sum Scale Option
Finally, let’s give an example of the constant sum scale question. This is asked in the following manner in your survey. It forces the respondent to slow down a bit and think about how important each factor is as they allot points.
Q: Using 100 points, please apply a number of points to each factor based on how important each are to you when buying a home. You must total 100 points divided among the factors.
A: Price, Location, School District, Inside Features, etc.
The respondent is given 100 points. They may choose to apply 80 to price, 15 to location, and spread out the remaining 5 points among other factors. When you analyze this data set, the differentiation between factors becomes evident. Most survey software will automatically tally and sum the point values to ensure they add to a constant sum of 100.