Why do we find some people more credible than others?


Messenger Effect

, explained.

What is the Messenger Effect?

The messenger effect is a cognitive bias that causes us to judge the validity or relevance of information based on its source. Instead of objectively analyzing the message’s content, our opinions of the person delivering the information affect our interpretation. 

Where this bias occurs

Imagine you are attending a workplace meeting. Everyone is there, from the interns to the CEO. While discussing strategies for the company’s direction, Josh, a junior-level employee, raises his hand. He shares his idea about packaging a new product to make it more appealing to younger customers. The response is underwhelming, and the brainstorming session quickly resumes. 

Around 15 minutes later, Marta, a senior manager, shares an idea that is nearly identical to the one Josh mentioned earlier. However, this time, the CEO and other leadership seem very excited about the idea, and the meeting topic shifts to how to set “Marta’s plan” in motion.

This hypothetical company meeting demonstrates the power of the messenger effect. Josh’s idea wasn’t ignored because it was bad. It was ignored because he was the one who shared it. Josh is fairly new to the company and has very little experience. When Marta reintroduces the idea, her track record of success and reputation for innovation lend the idea more credibility. As a result, the leadership team is much more interested in exploring her suggestion.

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Individual effects

The messenger effect can lead to poor decision-making by disrupting our ability to critically evaluate information. Instead, we use our opinion of the messenger as a shortcut for assessing the validity of the message. If we believe the messenger is credible, then we are more likely to accept the information at face value. The opposite is also true. If we do not trust the source, then we are more likely to dismiss their message, even if the content is objectively factual. 

As a result, the messenger effect can increase our vulnerability to misinformation. For example, some people may trust social media posts shared by friends or family members, even if the content contradicts the leading opinions among experts.

Systemic effects

The messenger effect has wide-reaching implications in nearly every area of society. One area where this effect is especially salient is public health. 

People will only act on information from sources that they find credible, which, in the case of a serious public health crisis, could mean that lives are at stake. For this reason, institutions and governments must select the right messenger(s) to influence public behavior. 

The messenger effect can also influence policy, as it takes the right person for large institutions (such as government bodies) to act on behalf of the public.

The messenger effect was one of many factors that led Congress to hold its first UFO hearing in nearly half a century. However, over those 50 years, tens of thousands of people had reported seeing or even interacting with alien spacecraft. Politicians only began taking these claims seriously after several high-level military and intelligence officials began to share their encounters with UFOs and other unexplained phenomena.

Personnel at the Office of National Intelligence also compiled many of these sightings into an unclassified report and requested an investigation. As these officials had long, untarnished careers and held high-level security clearances, their credibility helped validate their claims. Testimony from these highly credible messengers was enough to spur Congress into action.

As the example above demonstrates, until the right messenger comes along, a topic may not receive the resources and attention it deserves. If factual information comes from someone who is perceived as untrustworthy, people judge the validity of the claim solely based on their interpretation of the person. 

This distrust can cause people to outright reject advice or recommendations, even if these suggestions would improve their outcomes. The wrong messenger can make people resistant to changing their behaviors. This can cause problems to become entrenched and even more difficult to solve. In many cases, this reaction can worsen outcomes for the whole of society. 

The topic of climate change is a textbook example of the power of the messenger effect. Despite the growing body of evidence and near-unanimous consensus amongst environmental scientists that climate change is caused by man-made activities, recent surveys show that more than half of Americans don’t agree. 

One reason for this discrepancy is distrust of climate scientists and the media outlets that report their findings. People who do not view researchers as credible messengers are more likely to believe that climate change is a natural phenomenon or that the Earth isn’t warming at all.1 

As a result, these Americans are far more likely to oppose legislation designed to combat climate change and question the true motive for these policies. This can make policy changes move very slowly and affect how well the government can tackle climate change.

How it affects product

The messenger effect’s influence on people’s behavior choices and decision-making can be harnessed in product design and marketing. Digital product designers can leverage the messenger effect to increase product interest. For example, companies can pay an influencer whom their target customer base views as a credible messenger to demonstrate the new product. 

Viewers will transfer their interpretation of the influencer onto the product. So, if the influencer is known for being organized and efficient, viewers may unconsciously believe that the digital product also has those same qualities. 

For example, when the crypto exchange platform FTX debuted, the company invested heavily in credible messengers, such as celebrities, business leaders, and financial influencers to assure potential customers of its security and stability. 

People who trusted these celebrities' and influencers’ opinions would transfer this credibility to their opinion of FTX. This would make them far more likely to open an account and deposit their money in the exchange.  

Although the exchange was endorsed by a variety of celebrities, the majority of credentialed financial professionals shunned FTX and refused to promote it on their platforms or to their clients. A key reason for this is that professionals in the conservative and heavily regulated finance industry need more evidence of stability and sustainability before promoting a new financial product.

The Messenger Effect and AI 

The messenger effect can be amplified by AI as Deep Fake software makes it possible for anyone to benefit from the effect without the need to build credibility or gain a reputation. Instead, they can simply make a video or audio of a credible messenger sharing the information they want to disseminate. 

For example, someone could create a Deep Fake video of a respected politician announcing their support of an unpopular policy. In October 2023, a Deep Fake of President Biden reinstating the draft and sending American soldiers abroad quickly went viral. Although the earliest versions of the video were clearly labeled as AI, the clip was copied and shared without this disclaimer. As a result, many people took the message at face value. 

While a quick fact-check would have been enough to discredit the video, the messenger effect prevented many people from doing so. The video was enough to fuel rumors that a military draft was imminent.

AI can also make leveraging the messenger effect in scams easier by personalizing the voice used to make a demand. While a person may ignore a phone call from a stranger asking for money, they may be more convinced if the voice on the other end sounds like a family member or friend. 

Fraudsters can also use AI to spoof identities associated with authority and credibility, such as government agencies or financial institutions. People may be fooled by an authoritative-looking website, email address, or message to share their sensitive information. The information request seems to come from a credible source, so people are less likely to question the website’s legitimacy. 

Why it happens

The cognitive processes behind the messenger effect are the focus of the book Messengers: Who We Listen To, Who We Don’t, and Why by authors Stephen Martin and Joseph Marks. In the book, Martin and Marks explain why we resort to mental shortcuts like the messenger effect when analyzing information. 

They found that when confronted with difficult, complex questions, we often do not have access to all the information we need to reach a thoughtful conclusion. So, to fill in the gaps, we include any judgment about the messenger in our analysis. We do this even if the messenger played no role in creating the content of the message.2 

The messenger effect is also compounded by other common cognitive biases, which can unconsciously shape our judgment of the messenger. These include the halo effect, the hot-hand fallacy, and in-group bias.

Why it is important

As mentioned before, the messenger effect has a powerful influence on whether or not people believe or act on information presented to them. This can have immense implications on individual well-being and the overall functioning of society.

The messenger effect can amplify the success of propaganda and disinformation (false information disseminated purposefully to mislead a particular group). People make decisions based on this faulty information, and eventually, these choices that are made at the individual level affect everyone as a whole. 

As mentioned before, the messenger effect is particularly harmful in terms of public health. In 1998, British physician Andrew Wakefield published a research paper linking the MMR vaccine to autism in young children.

Although larger studies have since disproven the findings, and the study itself has been revoked, many parents found Wakefield to be a credible messenger and followed his anti-vaccine advice. Reduced child vaccination rates in some communities have led to public outbreaks of once-rare diseases such as measles and mumps. 

The messenger effect can also help people make positive changes in their lives. For example, young, relatable personal finance influencers can convince people to open investment accounts and save for retirement. 

While this information is not new, previous messengers were often financial advisors, who typically used language that didn’t resonate with a wider audience. Today, social media platforms enable a new crop of credible messengers to share basic personal finance advice in a relatable, accessible way.

How to avoid it

The messenger effect is one of the most widely leveraged cognitive biases. It appears in marketing, public policy, and media. The messenger effect’s ubiquity makes it difficult to avoid, but recognizing and challenging it can reduce its influence. 

For example, before accepting any information from a trusted messenger, consider that it may contain flaws or errors. Look at several other sources from different industries and notice where the information overlaps and where it diverges. 

On the other hand, be wary of dismissing information simply because you do not trust the source. Checking a claim against various sources is a much more effective way of verifying information than judging the messenger.

How it all started

The messenger effect has been studied since the mid-20th century. In the 1950s, psychologists Carl I. Hovland and Walter Weiss investigated how much the author of an opinion piece influenced readers. The study aimed to examine how people remembered information over time. The experiment revealed that the messenger played an important role in how people interpret information. 

The researchers began the experiment by asking people to share their opinions on a particular topic. After the subjects shared their views, the researchers created a text expressing the exact opposite opinion. Five days later, these texts were shared with the subjects. Some people were told that the opinion pieces came from highly credible sources, such as expert scientists or journalists. Others were told the texts came from low-ranked magazines. 

When readers were told that a credible author wrote the opposing viewpoint, they were three times more likely to change their opinion than those who thought the source was not credible. All the arguments in the texts were the same. Only the messenger made the difference.

A previous study by Hovland of trustworthy and untrustworthy sources revealed an interesting long-term effect. Over time, subjects tended to remember the arguments but not the source. If the subject couldn’t remember if the information came from an unreliable source, they were much more likely to agree with the content of the argument. This highlights how much the messenger effect influences how people accept information.3 

Example 1 - In the Courtroom 

Litigators have always understood how a witness’ perceived credibility can sway a jury or judge. However, the power of the messenger effect is so strong that it can even influence how an absentee witness is perceived.

A 1983 study found that jurors’ interpretation of recorded witness testimony was influenced by the person’s demeanor. If the person appeared hostile or ill-tempered, the jurors had a more negative opinion of the witness. This occurred even if the person on the video was an actor filling in for an absentee witness and had nothing to do with the case.4

Example 2 - Emergency Room Visits

The messenger effect can impact how people use public services. The UK National Health Service (NHS) found that a combination of biases and perceptions, including the messenger effect, was causing parents to bring their children to the pediatric emergency room for minor illnesses. 

The parents’ behavior was driven by the belief that pediatricians were more trustworthy for diagnosing children than other healthcare practitioners, such as pharmacists or primary doctors. So, instead of getting advice from these sources, parents headed straight to the emergency room. 

The NHS found that parents were more likely to use self-diagnosis charts and home treatment resources if pediatricians approved or created the material.5


What it is

The messenger effect is a cognitive bias that causes us to judge the validity or relevance of information based on the person delivering the message.

Why it happens

When we are confronted with difficult, complex questions, we often do not have access to all of the information we need to reach a thoughtful conclusion. So to fill in the gaps, we include any judgment about the messenger in our analysis.

Example 1 – How the Messenger Effect Influences Jurors

A study from 1983 revealed that jurors' interpretation of recorded testimony could be influenced by the demeanor of a substitute actor, even if the actor had no connection to the case at hand.

Example 2 – How the Messenger Effect Increases Unnecessary Emergency Room Visits

The UK National Health Service (NHS) discovered that the messenger effect was one of the reasons parents brought their children to the Pediatric Emergency Room for minor illnesses. Many parents believed pediatricians held more credibility than other healthcare practitioners. The NHS used this effect to create pediatrician-approved self-diagnostic materials to teach parents how to care for children at home. 

How to avoid it

We can mitigate the influence of the messenger effect by critically evaluating information from trusted messengers, acknowledging the potential for flaws, and cross-referencing with multiple sources to identify patterns and discrepancies. 

Related TDL articles

The Power of Narratives in Decision Making

This article dives into our tendency to process the world through a coherent narrative or story. The messenger effect plays a part in this phenomenon, as the more we empathize with the storyteller, the more likely that their story will impact us. 

How Behavioral Science Can Build Products that Sell Themselves: The Pirate Funnel Toolkit

This article explains how businesses can leverage biases like the messenger effect throughout their growth strategy. The author specializes in applying behavioral science concepts to growth strategy and organizational outcomes. 


  1. Alvarez, R.M., Debnath, R., Ebanks, D. (2023). Why don’t Americans trust university researchers and why it matters for climate change. PLOS Clim 2(9): e0000147. https://doi.org/10.1371/journal.pclm.0000147
  2. Marks, J., & Martin S. (2019). Messengers:who we listen to, who we don't, and why. PublicAffairs.
  3. Hovland, C., & Weiss W. (1951). The influence of source credibility on communication effectiveness. The Public Opinion Quarterly, Winter, 1951-1952, Vol. 15, No. 4 (Winter, 1951-1952), pp. 635-650. https://www.jstor.org/stable/2745952
  4. Kassin, S. M. (1983). Deposition testimony and the surrogate witness: Evidence for a "messenger effect" in persuasion. Personality and Social Psychology Bulletin, 9(2), 281–288. https://doi.org/10.1177/0146167283092013
  5. Egan, M., Holden, B., Service, S., & Snijders, V. (2017). Why do parents bring children with minor illness to emergency and urgent care departments? Literature review and report of fieldwork in North West London. The Behavioural Insights Team. Imperial College London. https://www.bi.team/wp-content/uploads/2017/12/Why-do-parents-bring-children-with-minor-illness-to-emergency-and-urgent-care-departments-FINAL-BIT.pdf

About the Authors

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Dan Pilat

Dan is a Co-Founder and Managing Director at The Decision Lab. He is a bestselling author of Intention - a book he wrote with Wiley on the mindful application of behavioral science in organizations. Dan has a background in organizational decision making, with a BComm in Decision & Information Systems from McGill University. He has worked on enterprise-level behavioral architecture at TD Securities and BMO Capital Markets, where he advised management on the implementation of systems processing billions of dollars per week. Driven by an appetite for the latest in technology, Dan created a course on business intelligence and lectured at McGill University, and has applied behavioral science to topics such as augmented and virtual reality.

Sekoul Krastev's portrait

Dr. Sekoul Krastev

Sekoul is a Co-Founder and Managing Director at The Decision Lab. He is a bestselling author of Intention - a book he wrote with Wiley on the mindful application of behavioral science in organizations. A decision scientist with a PhD in Decision Neuroscience from McGill University, Sekoul's work has been featured in peer-reviewed journals and has been presented at conferences around the world. Sekoul previously advised management on innovation and engagement strategy at The Boston Consulting Group as well as on online media strategy at Google. He has a deep interest in the applications of behavioral science to new technology and has published on these topics in places such as the Huffington Post and Strategy & Business.

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