The Mental Mapping of Magnitude



Researchers have the option of choosing between typical numeric scales that are horizontal, with numbers increasing from left-to-right, or vertical, with numbers increasing from top-to-bottom. Do responses elicited on such horizontal scales differ from those elicited on down-oriented vertical ones?  Results from five experiments (N=2198) show a scale orientation effectwhere the spatial-numeric orientation of response format systematically alters participants’ responses. For consequential measures such as Net Promoter Score and commonly used life satisfaction measures, responses measured on top-to-bottom vertical scales were lower than those on left-to-right horizontal scales. We propose this is because numeric magnitudes are associated with spatial orientations in the human mind. In the horizontal dimension, increasing numeric magnitude is mentally represented from left to right, consistent with the mapping of the left-to-right horizontal scale. In the vertical dimension, increasing numeric magnitude is mentally represented from bottom to top, inconsistent with the mapping of the top-to-bottom vertical scale. As a result, the top-to-bottom vertical scale feels less fluent and intuitive, biasing responses. Reaction time measures support this explanation. The results suggest that scale format itself can induce feelings of disfluency and that practitioners and researchers should avoid disfluent scales. 

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