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Tourangeau, Roger, Mick P. Couper, and Frederick G. Conrad. 2007. "Color, labels, and interpretive heuristics for response scales." Public Opinion Quarterly, 71:91-112.
We carried out two experiments to investigate how the shading of the options in a response scale affected the answers to the survey questions. The experiments were embedded in two web surveys, and they varied whether the two ends of the scale were represented by shades of the same or different hues. The experiments also varied the numerical labels for the scale points and examined responses to both unipolar scales (assessing frequency) and bipolar scales (assessing favorability). We predicted that the use of different hues would affect how respondents viewed the low end of the scale, making responses to that end seem more extreme than when the two ends were shades of the same hue. This hypothesis was based on the notion that respondents use various interpretive heuristics in assigning meaning to the visual features of survey questions. One such cue is visual similarity. When two options are similar in appearance, respondents will see them as conceptually closer than when they are dissimilar in appearance. The results were generally consistent with this prediction. When the end points of the scale were shaded in different hues, the responses tended to shift toward the high end of the scale, as compared to scales in which both ends of the scale were shaded in the same hue. Though noticeable, this shift was less extreme than the similar shift produced when negative numbers were used to label one end of the scale; moreover, the effect of color was eliminated when each scale point had a verbal label. These findings suggest that respondents have difficulty using scales and pay attention even to incidental features of the response scales in interpreting the scale points.