Choosing the Right Scale

This article focuses on the available scales one can use for research including odd or even numbered scales, range of points and the labeling of the scale.

Choosing a scale for your survey instrument is an important decision that will shape the information you collect. In the research field, there is much discussion as to how many points and what kinds of scale labels (anchors) comprise the most effective measurement tool. Each scale has variations, some more reliable than others. This newsletter discusses pros and cons of the scales most commonly used for mail surveys, and the three scales which perform the best according to current research.

Even vs. Odd

Even numbered scales can more effectively discriminate between satisfied or unsatisfied customers because there is not a neutral option. However, this clear division may cause hesitation for respondents who are neutral in regard to a survey item. Without a midpoint option, respondents often choose a positive response, creating positively skewed data. Carefully consider whether a clear division between positive and negative responses is necessary, or whether a midpoint will be more appropriate for your information needs.

Number of Points

In survey research, scales commonly range from 2 to 10 points. The number of points for your scale should be determined by how you intend to use the data. Although seven to ten point scales may seem to gather more discriminating information, there is debate whether respondents actually discriminate carefully enough when filling out a questionnaire to make these scales valuable. Also, these scales are often collapsed into three or five point scales for reporting purposes. Four and five point scales are more highly recommended; some are discussed later in this issue. Two and three point scales offer little discriminative value and are rarely recommended for satisfaction research.

Note: Scales, whether odd or even, are sometimes misused. Scale point definitions may be written to offer more positive options than negative options, resulting in positively skewed data. It is risky to make business decisions based on these data.

Defining Your Scale

Once the number of points on a scale has been decided, it is important to determine the labels for each scale point, or in some cases, whether or not you will use any labels. Some researchers prefer to anchor the end points, meaning only the first and last scale points are defined with words. The rationale behind this method is that it provides a "nominal" scale with equal intervals between each scale point, defined by numbers. For example, an agreement scale could be set up like this:

Researchers using this approach argue that it also avoids respondents making more subjective decisions about the differences between word labels for each scale point. Though this may be true, it is also important that each respondent understand the meaning of each scale point. By labeling each scale point, all respondents attach the same word to a numerical value. This helps avoid respondent misinterpretation of scale definitions. Additionally, verbally defining each scale point allows reports to be written in more concrete terms such as: "x percentage were satisfied."

Whether you decide to define all of your scale points, or only some, the labels attached can affect the validity of your survey. Survey scales have been tested again and again through the years, and certain scales appear to produce more accurate data than others. The best scales to use for mail surveys, according to current research, are listed and described below.

Recommended Scales

The following paragraphs discuss information from current research, particularly: Devlin Marketing Research, Vol. 5 #3, Peterson, Journal of Consumer Research, Vol. 21, September, and the 1994 research presentation by BELLCORE at the ASQC/AMA Customer Satisfaction Measurement Conference.

Four-Point Requirements Scale

Receives high marks for discrimination and reliability. A leading sentence might be, "Please indicate how well Company Z met your requirements."

Exceeded	Met	Nearly Met	Missed
4	3	2	1

The option of "Nearly Met" serves well to capture data from respondents who are somewhat unsatisfied but prefer to choose positive responses.

Five-Point Expectations Scale

Receives high marks for discrimination and reliability. A leading sentence might be, "In terms of your expectations, please rate the performance of Company Z."

Significantly Above	Above	Met	Below	Significantly Below
5	4	3	2	1

Five-Point Satisfaction Scale

Works well for mail surveys, but does not discriminate high-end performance to the degree of the expectations and requirements scales. Even so, we often use this scale for satisfaction surveys because it asks directly about the level of satisfaction: precisely what we want to measure, and it conveys to your customers that their satisfaction is your main concern.

Note: While these scales have been shown to be effective in collecting accurate data, a good scale cannot compensate for poorly worded items. Accurate, reliable data depends on a combination of the proper scale and correctly written items, as well as proper survey administration.

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