SOKOLOVA, KRISHNA, AND D € ORING
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TABLE6
STUDY 2A: PACKAGING STIMULI
Plastic condition
Plastic+paper in 1:0.5 proportion condition
Plastic+paper in 1:1 proportion condition
Plastic+paper in 1:2 proportion condition
Results A one-way ANOVA on participants’ PEF scores ( a ¼ 0.93) revealed a significant main effect of packaging type on PEF ( F (3, 797) ¼ 30.15, p < .001, g 2 p ¼ 0.102). Simple contrasts showed that plastic-only packaging was per- ceived as less environmentally friendly compared to each of the other three plastic þ paper packaging types (all p s < .001). Importantly, consistent with the proportional reasoning account, the effect of adding paper to plastic was weaker when the paper-to-plastic proportion was small ( M plastic ¼ 2.16, SD ¼ 1.14, vs. M 1 plastic þ 1 = 2 paper ¼ 2.91, SD ¼ 1.20, F (1, 797) ¼ 32.62, p < .001, g 2 p ¼ 0.039) than when it was medium ( M plastic ¼ 2.16, SD ¼ 1.14, vs. M 1 plastic þ 1 paper ¼ 3.06, SD ¼ 1.34, F (1, 797) ¼ 47.50, p < .001, g 2 p ¼ 0.056), or large ( M plastic ¼ 2.16, SD ¼ 1.14, vs. M 1 plastic þ 2 paper ¼ 3.34, SD ¼ 1.48, F (1, 797) ¼ 83.58, p ¼ .001, g 2 p ¼ 0.095). A separate regression on the subsample of the three “plastic þ paper” conditions with the paper-to- plastic proportion as a continuous independent variable confirmed that as the proportion of paper in product pack- aging increased, the PEF scores increased ( b ¼ 0.28, SE ¼ 0.09, t ¼ 3.26, p ¼ .001).
Discussion By demonstrating that the PEF bias is stronger (weaker) when the paper-to-plastic proportion in packaging is large (small), study 2a provides evidence for the proportional reasoning account of the PEF bias and against its averaging account. One may argue that it is the absolute, not the relative amount of paper in product packaging, that drives the PEF bias. That is, the more paper there is in product packaging, the greater its perceived environmental friendliness. Data from studies 1a to 2a are indeed consistent with both the proportional and absolute amount of paper accounts of the PEF bias. To probe the absolute amount of paper account, we ran a follow-up study, where we compared the effect of adding paper to plastic and the effect of adding paper to paper (study A, web appendix D). Under the absolute amount of paper account, packaging comprised of one layer of paper should have lower PEF compared to packag- ing comprised of two layers of paper. By contrast, under the proportional reasoning account, one-layer and two- layer paper packaging should have similar PEF, since in both these cases, the packaging is composed of 100% paper. The results were consistent with the proportional
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