Research Article: Testing the decoy effect to increase interest in colorectal cancer screening

Date Published: March 26, 2019

Publisher: Public Library of Science

Author(s): Sandro Tiziano Stoffel, Jiahong Yang, Ivo Vlaev, Christian von Wagner, Matthew Quaife.


Literature on consumer choice has demonstrated that the inclusion of an inferior alternative choice (decoy) can increase interest in a target product or action. In two online studies, we tested the impact of decoys on the probability of previous non-intenders to have a screening test which could significantly lower their chances of dying of colorectal cancer. We find that the presence of a decoy increased the probability to choose screening at the target hospital (over no screening) from 39% to 54% and 37% to 59% depending on how many hospital attributes were communicated and how strongly the decoy was dominated by the target. We also show that the presence of the decoy was associated with lower levels of reported decisional complexity while not undermining information seeking and knowledge acquisition. These findings offer a ‘proof of principle’ that decoys have the potential to increase screening uptake without negatively influencing informed choice.

Partial Text

Human decision-making can be influenced or ‘nudged’ in a predicted direction through careful manipulation of choice setting [1]. One classic example of how individual preferences can be influenced is the decoy effect, whereby the introduction of a less attractive alternative (i.e. a decoy) into a choice set increases the probability of the more attractive target or action being chosen [2;3].

Study 1 tested whether the principle of the decoy effect applies to a complex and unfamiliar decision that people face when invited for BSS.

The second study aimed to test whether dominance strength (i.e. the degree to which the decoy is dominated by the target) would moderate the decoy effect observed in Study 1. To vary dominance strength we manipulated travel and waiting time simultaneously to create a weak decoy (one of two attributes is undesirable) and a strong decoy (both attributes are undesirable). The second aim was to test whether the decoys would influence information seeking and knowledge about the harms and benefits of BSS.

This is the first study that tested the decoy effect in cancer screening. In two experimental online surveys, we showed that individual screening intentions can be increased by adding a decoy screening alternative to the choice set. Furthermore, we found that the decoy effect is influenced by the degree to which the decoy option was dominated by the target option. This shows that introducing carefully designed screening alternatives can not only increase the appeal of the target but also avoid choice overload [40].




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