Peer-Suasion

What it is

Cialdini introduces the word in Influence, as his own coinage for the finding that people are more inclined to follow the lead of their peers than of people unlike them. It names the similarity condition. Where uncertainty asks whether the buyer is unsure, and the many asks whether numerous others are doing the thing, similarity asks whether those others resemble the buyer.

The label belongs to the book. The underlying claim, that a reference group close to the target is more persuasive than a distant one, is an empirical claim, and it is tested in hotels. Goldstein, Cialdini and Griskevicius (2008) reported towel reuse of 44.1 per cent with a descriptive-norm card against 35.1 per cent for the standard environmental appeal in a first experiment. In a second experiment, a message citing guests who had stayed in the same room reached 49.3 per cent.

In effect

For a marketer, peer-suasion is a reason to choose the reference group carefully. A review total, a bestseller badge or a customer number describes a crowd, and the question is whether the reader sees that crowd as people like themselves. The same room is a very close crowd, and the same industry, city or job title are looser versions.

The mechanism is the same as in the Beijing restaurant experiment by Cai, Chen and Fang, where the ranking came from other diners at the same restaurant. The diners who knew least leaned on the crowd most. Similarity adds the question of which crowd, and the hotel study is the clearest test of that question in the field.

What it does not say

It does not say that closer reference groups always work better. Bohner and Schluter (2014) ran the towel experiment in two German hotels and tested the same-room norm. In their first study, the same-room norm was significantly less effective than the general hotel-guest norm. In their second, it was descriptively more effective, but the difference was not significant. Their reading is that the effect of closeness to the reference group was inconsistent.

It also does not say that a descriptive norm beats a plain argument. In the German hotels, norm messages beat no message but did not beat the standard environmental appeal.

And it is mostly one team's result. The original experiments came from Cialdini's own research programme, and the label comes from his book. The claim that survives is modest: similarity can add pull, and the size of the addition depends on setting.

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