In his book Influence: Science and Practice, Robert Cialdini identifies six principles of influence:

In this article, we discuss the second principle in this list: social proof.

Social proof is a psychological phenomenon where people reference the behavior of others to guide their own behavior. This tendency is driven by our natural desire to behave “correctly” under most circumstances—whether making a purchase, deciding where to dine, determining where we should go, what we say, who we say it to, and so on. One of the best examples of social proof, in real life, is the long line in front of an Apple Store on the day a new iPhone is released. The fact that a group of people find the new phone so desirable as to invest considerable time standing (or sleeping!) in line impacts our perception of the phone value (and makes us covet one, too).

people in line at Apple Store
Apple Store UK Opening Day photo by Lucius Kwok. Used via Creative Commons License.

If all these other people want it, it must be good. That’s why McDonald’s put up a sign saying “over 100 million hamburgers sold” in 1958.

In This Article:

Examples of Social-Proof Interface Patterns

Web 2.0 has popularized the practice of making users’ actions and opinions public with the intent of influencing and informing others. Here are just a few examples where the social-proof principle is at work.

Reviews

customer reviews
Adagio Teas uses reviews to influence prospective buyers: “If others like this tea, then maybe I’ll like it as well.”

Behavior (Social filters)

social filters
eBags displays related bags based on what other customers (who viewed the same page) also viewed; “If they viewed this bag, the others they looked at must also be something I would like.”

Opinion

people who like an item
In this example from Etsy, the interface includes a number and usernames of people who “admire” a particular item. Stores on Etsy often include unique or limited quantity of items, so the presentation of other interested parties is also tapping into the effects of the Scarcity principle.

Background of the Social-Proof Principle

Social proof is one of the 6 influencing principles detailed in Dr. Robert Cialdini’s book Influence: The Psychology of Persuasion (first published in 1984). As a psychology professor, Cialdini and his students conducted numerous research studies to identify and prove these principles. Social proof plays off our insecurities and desire to do the “right thing.”

Occasionally, in usability studies, users tell us that they don’t care about user reviews, they don’t trust other people’s opinions, and they make all of their decisions based totally on their own independent perspective. Unfortunately, thousands of psychology studies prove this “lone wolf” theory to be quite false — another example of why we should base design decisions on what users do rather than what they say.

Social-psychology studies have repeatedly indicated our conscious and unconscious reliance on each other for cues in almost all decisions that we make. One of the most ubiquitous uses of social proof is the universally disliked “laugh track” used in sitcoms. Cialdini notes, “Experiments have found that the use of canned laughter causes an audience to laugh longer and more often when humorous material is presented and to rate the material as funnier. In addition, some evidence indicates that canned laughter is most effective for poor jokes.”

When to use the technique

Increasing credibility: Users do consider how others perceive content, services, and products that they find online. Adding an indication that other people, or even better, familiar people, like the content or product can remove decision-making uncertainty.

Encouraging adoption and acceptance: If you’re trying to get people to subscribe to a newsletter or follow a Twitter account, communicating that you already have a large number of subscribers can increase subscriptions because it indicates that others like your content. (Example: the subscription page for our own newsletter. Please indulge us in using our own site as a good example just this once :-)

Testing Social Proof

The most significant risk with using social proof is the perception that too few people approve of the piece of content, service, or product. In a recent usability session, a user looked at the number of people who had shared an article and stated that the article wasn’t popular enough, so maybe it wasn’t good.

When a study participant noticed that only 1000 people had shared the article on Facebook, she wasn’t impressed. Of course, the 17 G+ users are even less impressive.

The other risk of social-proof elements is making the interface too busy and (potentially) the page load too slow. Often social widgets result in complex backend communication with social-network sites (such as Facebook and Twitter) and significantly increase the response time of the site, especially on mobile devices or in locations with poor connectivity.

The following table lists the questions to ask and testing techniques to employ when you’re considering social proof:

QUESTION

TESTING/DATA

Which (if any) social-proof mechanisms increase conversions?

A/B testing of comments, reviews, likes and testimonials

Do social-proof features impact credibility?

Usability testing with task-specific follow-up surveys measuring confidence (e.g., “On a scale from 1-7, how confident do you feel in this selection?”) to elicit emotional response to the messaging.

Do users notice social-proof features?

Usability testing or eyetracking testing to measure attention and fixations allocated to social features. Lack of concentrated fixations could indicate the design or placement is poor. Also, task-based usability studies can be used for testing.

Do social-proof features overwhelm users?

Usability testing can indicate if social proof features lead to a crowded and confusing interface that distracts users from calls to action.

Do social-proof features slow down the page?

Assessing page loading time to determine whether it is reasonable for a variety of connectivity conditions.

Conclusion

The use of social proof in interfaces has become commonplace in many web environments. More sophisticated implementations not only indicate general adoption or preference, but highlight adoptees that are known persons (e.g., Facebook friends). Because of the success of social proof, some sites may over-use the technique and complicate simple interactions. This is why it is important to test the specific design implementations and not simply accept that any social proof feature is beneficial.

For more on social proof and other persuasion techniques, see our full-day Persuasive Web Design training course.

 

Reference

Robert B. Cialdini, Influence: Science and Practice, Pearson Education Inc., 2009.