The concept of ratio bias is rooted in our difficulties in dealing with proportions or ratios as opposed to absolute numbers. For example, when asked to evaluate two movie rental plans with a contracted scale (e.g. 7 and 9 new movies per week for Plans A and B, respectively) as opposed to an equivalent offering with an expanded scale (364 and 468 movies per year, respectively), consumers favor the better plan (Plan B) more in the scale expansion than contraction condition (Burson et al., 2009). This is because our experiential system—unlike the rational system—encodes information as concrete representations, and absolute numbers are more concrete than ratios or percentages (Kirkpatrick & Epstein, 1992). (See also framing, dual-system theory, affect heuristic.)
Burson, K. A., Larrick, R. P., & Lynch, J. G., Jr. (2009). Six of one, half dozen of the other: expanding and contracting numerical dimensions produces preference reversals. Psychological Science, 20(9), 1074-1078.
Kirkpatrick, L. A., & Epstein, S. (1992). Cognitive-experiential self theory and subjective probability: further evidence for two conceptual systems. Journal of Personality and Social Psychology, 63(4), 534–544.