Social Proof: the Wikipedia definition

Wikipedia defines social proof as:

…a psychological phenomenon where people assume the actions of others in an attempt to reflect correct behavior for a given situation. This effect is prominent in ambiguous social situations where people are unable to determine the appropriate mode of behavior, and is driven by the assumption that surrounding people possess more knowledge about the situation.

Social proof helps us make decisions more easily

But why do we need help deciding how to act? Surely we are capable of making our own decisions independent from the opinions or actions of others?

We are, but this is often difficult and can require either a lot of time or a large degree of mental effort, both of which are commonly in short supply!

Observing the behavior of those around us provides a convenient mental short cut which simplifies the decision process for us.  “We determine what is correct by what other people think is correct” (Lun et al, 2007).

Perhaps the most notable experiment (which most of us social scientists wheel out in articles like these!) was the 1969 experiment performed in New York by Milgram, Bickman & Berkowitz.

These researchers proved that a group of four or more people standing on the sidewalk looking up at the sky will cause 80% of passers-by to perform the same action.

We all want to make fewer mistakes

Our goal when striving to make ‘the right decision’ is actually to avoid making a mistake. If you think back to caveman days a mistake could cost you your life: choosing the wrong weapon, attacking the wrong animal, drinking from the wrong puddle etc.

So we rely on social proof as a survival technique to help us make fewer mistakes.

Three factors determine how much influence social proof has on us: scale, similarity and ambiguity

The degree to which we are influenced by social proof is affected by three things:

  1. The number of people performing the behavior (scale).
  2. How similar we perceive those people to be to ourselves (similarity).
  3. The level of ambiguity or difficulty presented by the decision or environment  (ambiguity).

Scale increases the persuasive power of social proof

In the experiment where people on the sidewalk were staring up at the sky it was found that when only one person was staring up at the sky only 40% of people passing by performed the same action.

When the number of people staring up at the sky was increased to five the percentage of people copying the behavior increased to 80%.

As the number of people performing the same behavior increases so too does the degree to which we are influenced by that behavior.

We are more influenced by people we perceive as being similar to ourselves

Cialdini describes another experiment (Bandura & Menlove, 1968) in which researchers proved that the most effective way to rid children of their phobias of dogs was to expose them to frequent films depicting many other children playing happily with dogs.

After only four days of treatment 67% of the affected children were willing to climb into a playpen with a dog and remain confined there petting the dog while everyone else left the room.

We use the actions of others to decide on proper behavior for ourselves especially when we view those others to be similar to ourselves (Park, 2001).

As ambiguity increases so too does our susceptibility to social proof

This story is a great example of how a lack of familiarity causes ambiguity and how social proof can be used to overcome it:

Sylvan Goldman was a grocery store owner who noticed that people only purchased what they could physically carry in their shopping baskets. To remove this limitation he created the shopping trolley which was initially just a folding chair on wheels with a couple of baskets attached.

The problem though was that no one was using them despite placing a great number of them in a prominent area at the opening to the store complete with a sign and instructions.

Eventually Goldman hired fake shoppers to use the trolleys by walking around the store and filling them with products. It wasn’t long before his ‘true’ shoppers began following suit.

Sylvan Goldman had invented the shopping trolley and died a very, very wealthy man.

How to use social proof in Experience Design

The best way to use social proof to increase conversions is to first identify where users are most likely to be susceptible to this form of influence. 

Start by analyzing your conversion journey stage by stage.  At which point is the decision to act made more difficult by unfamiliar information or choices?  This is likely to be the phase during which prospects are introduced to product choices with features or benefits that are either confusing or poorly understood.

Ultimately, you’re trying to find the point where making ‘the right choice’ becomes most ambiguous.  This is the point at which you should test introducing a form of social proof.

Practical techniques to use social proof

The most commonly used mechanism to use social proof is star ratings. These are simple indications that represent the opinion of others.

Star ratings can be provided with or without context. In this example, the star rating is simply displayed next to the product without any explanation of how the rating was derived, what the rating means or who has created it:

Star rating with no context from Expedia 2013

In this example from Amazon you can see that the star rating benefits from context such as who left the rating and how they came to arrive at their decision.

This interface also makes it possible to find out more about the reviewer. This helps users to assess similarity:

Star rating with context from Amazon 2013

In this example below you can see that the design includes scale, a factor known to boost the effectiveness of social proof. The star rating is presented as the average opinion of a specified number of people:

Ratings with scale from Play

This example (again from Amazon) shows how scale and context can both be used to add relevance and influence to social proof.

This block appears before all reviews and serves to communicate the number of reviews with each rating level (scale and context), the overall average with total number of reviews (scale) and a button label that explains that these reviews have come from other customers (similarity):

Scale and context from Amazon 2013

This example is another example of social proof with the benefit of ‘simplified relativity’. By ranking choices in sequence like this you help to short cut the mental process even further by eliminating the need for people to choose between items with the same star rating. 

Ranking systems like these use weightings which take into account the number of times a particular rating has been applied to give greater credibility to similarly rated items with differing numbers of ‘votes’.

This form of social proof removes even more ambiguity and makes the decision process even easier:

Rankings can remove ambiguity

Other forms of social proof to increase persuasion

Star ratings and rankings aren’t the only objects at your disposal for leveraging social proof: you can use indicators of current or previous behavior too.

The most classic example of this technique comes from McDonalds:

Billions and Billions buy McDonalds

Surely the decisions of 1 billion people can’t be wrong?!  Surely this is a behavior I can safely follow? This technique is often seen on ecommerce sites where the number of times an item has been purchased is used to suggest ‘this is a popular (and right) choice’:

Number of items sold triggers social proof

Some travel sites take this technique further by adding the element of real time social proof (with the added layer of scarcity) to their holiday listings.

By dynamically displaying ‘the number of people currently viewing’ or ‘this hotel was last booked 10 minutes ago’ the message to prospects is ‘This is a choice that has been made recently by others; you’re safe to make the same choice too’:

Real time social proof adds relevance

This method has the added advantage of similarity: “I’m thinking of staying here now and other people have just decided to stay there too”.  This additional time-sensitive relevancy is more powerful than a review or indication of behavior that happened at some point in the past.

Testimonials are social proof tools that should be thoroughly tested too

Testimonials are used to best effect when their authors are perceived to be just like us.

In this example from Basecamp you can see how two forms of social proof are used in together: a large number describing how many people have recently made the same decision you need to make (scale), plus a testimonial that includes a link so you are able to assess just how similar they really are:


We are all susceptible to social proof as a persuasion mechanism. The three factors that determine how strong this influence is are scale, similarity and ambiguity.

  • Scale is perhaps the easiest factor to manipulate and only requires the display of a count that shows the total number of people who have expressed the same opinion or performed the same action.
  • Similarity relies on an understanding of your customer personas and their context of use.  Also consider using technology to communicate real time behavior as a form similarity.
  • Ambiguity on the other hand is slightly more challenging and often requires complex instruments like ranking systems to separate similarly rated items.

Start using social proof to increase your own website conversion rate by identifying the point in your conversion funnel where prospects are most likely to experience the greatest degree of uncertainty and ambiguity.

Choose a mechanism that communicates the scale and similarity of consumer behavior in a manner appropriate to your brand.

Finally, remember that you might not get it right first time so be sure to prove your new ideas using a/b or multivariate testing to find the one that works best for your various audience segments.