We are Jan Losby (a CDC employee) and Anne Wetmore (a former ORISE Fellow at CDC), members of the Evaluation and Program Effectiveness Team in the Division for Heart Disease and Stroke Prevention at the Centers for Disease Control and Prevention (CDC).
Inevitably when you start creating a survey and you are using a Likert scale, you’ll ask yourself “Which should I use, an odd- or even-numbered scale?” To help you decide which might be best for you, let’s look at the advantages and disadvantages of each:
Hot Tip #1: Choosing odd–all odd-numbered scales have a middle value, often labeled “neither,” “neutral,” or “undecided.” However, even when the mid-point is labeled, respondents may each have a different interpretation of this response category. In a 2009 study, it was shown that possible interpretations of the mid-point can be quite numerous (see link below).
Advantages of odd-numbered scales
- Can be appealing to respondents since there is an easy option to select
- If topic is highly sensitive, may be best to offer neutral point
Disadvantages of odd-numbered scales
- People may be less discriminating in response (respondents don’t take time to carefully consider all of the various response categories)
- May not be collecting accurate responses (the mid-point can mean different things to different people)
Hot Tip #2: Choosing even–for all even-numbered scales the neutral middle option is removed. This is sometimes called a “forced choice” method since the neutral option is not available to respondents.
Advantages of even-numbered scales
- People may be more discriminating, be more thoughtful
- Eliminates possible misinterpretation of mid-point
Disadvantages of even-numbered scales
- Respondents could become frustrated and not complete the survey
- May not be collecting accurate responses if respondents feel/or perceive being required to make a selection
There isn’t a simple rule regarding when to use odd or even, ultimately that decision should be informed by (a) your survey topic, (b) what you know about your respondents, (c) how you plan to administer the survey, and (d) your purpose. Take time to consider these four elements coupled with the advantages and disadvantages of odd/even, and you will likely reach a decision that works best for you.
- A 2009 AEA presentation on interpreting the mid-point “stuck in the middle.”
- A good list of Likert-type response categories for 3- to 7-point scales.
- A short resource on Likert scales – description and examples.
- A 2004 study looking at the effect of scale format (using 3 to 9 categories) on the reliability of Likert-type rating scales. (requires account)
Do you have questions, concerns, kudos, or content to extend this aea365 contribution? Please add them in the comments section for this post on the aea365 webpage so that we may enrich our community of practice. aea365 is sponsored by the American Evaluation Association and provides a Tip-a-Day by and for evaluators.