Survey Research Definitions: Central Tendency Bias

Have you ever created frequency distributions from particular survey questions, only to realize that some response options were chosen only a few times, and others weren’t chosen at all?  This can occur for many types of questions with ordinal or interval scales, and is especially common when likert scales are used.  When survey respondents or raters are hesitant to select choices at either end of a scale, a phenomenon called central tendency bias may be to blame.

Central tendency bias occurs when raters or market research respondents avoid using extreme response categories.  People may naturally tend to provide similar, "middle-of-the-road" responses or ratings for multiple items, unless they already hold very strong opinions one way or the other toward the question topics.  Central tendency bias can work in tandem with habituation and acquiescence, producing results with little variation (and little insight!).

This source of error is especially prevalent in performance appraisals and employee evaluations.  For example, managers may be asked to rate their employees on a 5 or 7 point scale, and most workers will likely fit somewhere in the middle or upper-middle of those scales.  You might have heard of a supervisor that “never gives the highest rating” (regardless of worker quality), or a manager that rates almost everyone as “average.”

In general, you want to design survey response scales that will produce good variation.  Ideally, you’d like to see responses dispersed throughout the options included in your scales.  To be sure your response scales are appropriate, conduct a pretest (or "pilot") to test for central tendency bias (and many other sources of error).  In addition, a company can employ a forced distribution employee appraisal system, where supervisors and managers must rate workers on a relative scale, ensuring that employee ratings will vary and that distinctions can be made.

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