The Principle of Social Proof: The Power of Crowds




Persado’s mission is to help companies inspire their audiences to act, and the platform does this by organizing and quantifying emotional triggers in language and images.

But influence and persuasion is a vast field, and there’s always something more you can learn.

In our series on how tech can help your brand’s reach and influence, we’re exploring the Six Principles outlined in Robert Cialdini’s seminal text, Influence: The Psychology of Persuasion.

We’ve already talked about how to use The Reciprocity Principle, The Likability Principle, and The Commitment & Consistency Principle in digital marketing. This week, we’ll take a look at the Social Proof Principle.


In 1968, the social psychologists Stanley Milgram (best known for his experiment on obedience to authority figures), Leonard Bickman, and Lawrence Berkowitz performed an experiment around the idea of social influence, also known as The Street Corner Experiment.

First, they asked a single person to stand on a street corner and stare at the sky for 60 seconds. Very few passing pedestrians took note enough to also look into the sky. Most ignored him.

So the team put out a group of five to stare into the sky, and it quadrupled the number of passersby who became lookersup.

With 15 people standing and staring at a single spot in the sky, 45% more pedestrians stopped to join them.

When the first iPod debuted, the clever bastards at Apple took note of the phenomenon of social proof, foregoing the consensus ubiquity of black headphones in favor of clean white earbuds. Why? Because no one can see a thousand songs in your pocket, but they can see that everyone around them uses the same sleek-looking (yet actually quite crappy) headphones. As iPod use increased, the sense that iPods were everywhere increased even though you couldn’t see them.

Robert Cialdini outlines five basic modes of social proof, each of which we’ll pick through to see how they can be used in the digital setting.


In the untamed morass known as the internet, there are three types of expert reviews: “authority,” “affiliate,” and “associated.”

Authority reviews and endorsements are the most powerful. Just look at the stranglehold Wirecutter and Sweet Home have on almost every purchase decision, from the quite intimidating


This is the best kind of expert endorsement and the most difficult to ensure. You basically just have to be the best, which you should be anyway.

While these sites do make click-through cash, it’s usually from Amazon or other vendors, not the companies being reviewed. Keeping things aboveboard engenders much greater trust. That’s what social proof is all about.

Affiliates, on the other hand, run the gamut regarding how seriously people take them. NerdWallet commands some hefty respect in the personal finance world. But NerdWallet is incentivized to give good reviews because they get paid by the financial institutions they review. This risks causing some skepticism. That said, NerdWallet successfully counterbalances their personal stake with user reviews (more on that below).


The overhead for this kind of endorsement is relatively low — typically cost-per-conversion — and if the site is well-respected, it’s worth it, though many niche affiliate review sites are content-mill, fly-by-night side hustles for their creators.

And then there are Associated Experts. These are experts you sponsor to review your products or services. They could be blurbed on your site or commissioned for reports.

Take Headspace’s approach. Headspace is a daily guided meditation app that sponsors research into the effects of meditation and lists their published papers right on the site.


To make a big impression, you’d do well to implement the latter two while submitting your product to the scrutiny of Authority sites, where even if you get a less than stellar review, you’ll know where to improve.


Let’s focus on what you can do to ensure an endorsement: pay for it.  

There was that one lucky time that iGrill’s site crashed from overwhelming traffic minutes after a nod from Mark Zuckerberg, but that’s the result of having a good product and a lucky turn. Not necessarily something you can strategize. The Colbert bump is an equally lucky break.

But you can engineer such a moment to look like a lucky turn!

The typical celebrity endorsement is less about social proof than it is about flexing your brand by associating it closely with another brand, that of a public figure.

But the new generation of celebrity and influencer endorsements can be subtler, more targeted, and probably a lot cheaper.


If your chosen celebrities and influencers do it right, their day-in-the-life shots will seem more ingenuous, and thus more convincing, than a glamor shot otherwise would have. (The above is probably not the best example.)

Another aspect of this is making full use of the halo effect whenever you can. If you’re in B2B especially, client and partner logos should be prominent on your site, and you should drop names like they are combustible Samsungs. Build a library of branded case studies with your most recognizable clients. And flash logos related to any and all media mentions. This is not the time to be humble.


This is the time to be humble.

A study from found that “products with reviews have a 12.5% higher conversion rate than those without,” and products, “with 20+ reviews have an 83.85 higher conversion than those products without reviews.”

If you have a product or service that suits the Amazon-style star rating, let yourself be rated wherever you can, permitted they’re respected outlets with decent traffic. If you host your own reviews, be equally hospitable to good and bad reviews. Otherwise, your site will look rigged. If you’re really, truly so good that everyone is giving you five-star, stellar reviews, ask your mom to log in and give you a three-star review to at least make things look balanced.

But if your business is not the kind that can be easily summed up in an Amazon-style review, be sure to get customer testimonials for your site, and preferably post each one with a picture of the customer. When it comes to social proof, a face is more powerful than a name.


For a product site, emphasizing bestsellers — even if they’re not actual bestsellers — will turn them into bestsellers. More than anything, internet commerce illustrates the paradox of choice, so by creating a “cream of the crop” category, you relieve some of the burden.

New York Times bestsellers get on the list by supposedly being good books, but much of their staying power can be attributed to the promotional boost they get just by being on the list in the first place. This is why authors hustle so hard to get books pre-sold. It’s easier to stay on the list than it is to get on it.


The Wisdom of Crowds is how Amazon tries to upsell you every time you shop.


McDonald’s used this strategy to iconic effect by featuring counters on their signs to announce how many burgers they’d sold to date. Eventually, it became too many to count. Returning to Headspace as a prime example, they do the same thing to encourage users to meditate:



Here’s a quote from a press release regarding a 2015 Nielsen study:

The most credible form of advertising comes straight from the people we know and trust. Eighty-three percent of online respondents in 60 countries say they trust the recommendations of friends and family, according to the Nielsen Global Trust in Advertising Report released today.

There are two great ways to take advantage of this. The first is to connect is leveraging Facebook, the way Yelp, TripAdvisor, or TicketFly do, showing the places and events that friends have gone to and future plans they’ve confessed to online.


The second easiest way to capitalize on others’ social capital is to simply ask for and incentivize referrals, which so many subscription sites do already.


There you have it! Your five steps to influence through social proof!

Join us next week to learn how to use Cialdini’s Authority Principle to boost your emotional marketing efforts!

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