If you want the TLDR, or prefer visuals to text - give the slideshow a spin! Otherwise, scroll once or twice to join me in the text version.
Let's start with the definition.
The argument dilution effect is a phenomenon where the strength of an argument is diluted when it is presented alongside weaker arguments or irrelevant information.
You interact with this effect all the time in every day life. A few salient example areas: marketing campaigns, politics, corporate decision making, personal debates, negotiations, interviewing/hiring. Besides it's academic value to me, it fits within a larger area I'm personally and professionally enamored with: decision science.
Whether you share my interest in decision science or not (I think you should), you're not immune to the consequences of this pernicious problem. The argument dilution effect produces worse decision making and/or a lack of action. Awareness and identification of the cognitive bias better equips one navigate the world. Specifically, to critically evaluate the strength of arguments and make more informed decisions.
Back to the definition - when I read it twice, it sounds somewhat obvious. Weaker or irrelevant information doesn't sound like it will make an argument stronger. But in applied settings, it's quite counter-intuitive. Especially verbally. Let me show you with a quick example:
Compare these two offers:
Offer #1
Join an exclusive research community of leading scientists and rising stars in their respective fields.
Offer #2
Join an exclusive research community of leading scientists and rising stars in their respective fields. Each new member receives a $25 Starbucks gift card, a customized t-shirt, and access to future networking opportunities. Community members receive a monthly digest with news from the community.
If you're like most folks - Offer #1 is more persuasive. A computer prefers offer #2, you get more benefits. And the marketer who wrote offer #2 probably thought the same thing as the computer. We have all these great benefits, surely offering more of them makes the offer more persuasive.
It's a simple and often unrealized calculation misfire.
Often we assume the recipient of our arguments will add the pieces of evidence together. More evidence makes for a stronger case. Or at least that's the rational assessment. Contrary to the economics textbook, rationality is a flawed assumption. We humans toggle between rationality and irrationality on regular basis, depending on the environment.
When humans are presented with multiple pieces of evidence/information when making a decision, we tend to minimize the cognitive effort required (efficient or lazy, depending on your POV). Instead of determining the relative strength of each and weighing them all - what we actually do is average them all.
In most cases, we do a pretty sloppy average. We grab the strongest and weakest parts, then determine the total average is in the middle. This way, we don't have to examine each one or go through the onerous task of weighing them all. It's the shortest route to get to a 'good enough' answer and proceed to all the other useful things our brains want to do.
Sure, part of the responsibility lies with the recipient. They must assess whether the task at hand is worth the extra effort, and we don't always get that right. I'm more interested in the responsibility of the communicator - who can remove this problem before it exists.
Let's go into a few real world examples of this from recent history.
The O.J. Simpson murder trial:
The defense team presented a large amount of evidence, including irrelevant information about the victim's personal life, and copious details about subjects tangential to the charges. By presenting a confusing and overwhelming amount of evidence, the defense team made the jury's job much more difficult (think reasonable doubt).
The defense team argued that the Los Angeles Police Department was racist and had a history of framing black celebrities for crimes.
The defense team went into great detail about the science of DNA testing.
The defense team made a big deal about the fact that Simpson had a cut on his finger on the day of the murder.
The defense team attacked the character of the victim, Nicole Brown Simpson, by presenting evidence of her drug use and infidelity.
2016 US Presidential Campaign Debates:
Donald Trump used this effect masterfully. Primarily to deflect criticism and muddy subjects in the voter's mind. Constantly interrupting, introducing auxiliary or controversial evidence, making personal attacks, and expanding the scope of topics rapidly. He is certainly not the first or only politician to use this, in fact it's rare if a politician doesn't - it's just a well known and well done example.
When asked about his controversial comments regarding women, he'd talk about about ISIS, taxes, and Clinton's emails.
When asked about his tax returns, he'd talk about the United States' trade deficit and China's currency manipulation.
I'm going to get into a few research papers about the dilution effect. But before I do, I want to quickly acknowledge this is a mistake I make all the time. For me, there's nothing quite like a comprehensive, air tight, and impregnable argument. And that's how I like to consume information. I typically will weigh all of the components and then sum them together. Which as a communicator, makes me more susceptible to the error.
All that is to say, if you're learning about this as you read - I'm learning about it as I type. I'm right there with you.
Now, let's take a look at 3 studies where the researchers demonstrated this effect in different contexts.
The big take away:
Drug advertisements are required by the FDA to list severe and frequent side effects. This translates to a slew of both serious and minor side effects, usually jammed into the end of an ad by a hurried female voice. The mixture of serious and minor side effects dilutes consumers’ judgments of the overall severity of side effects, compared to when only the serious side-effects are listed.
How they looked at it:
Participants were randomly assigned to one of four conditions in Study 1 and Studies 2a-c. The four conditions were: (1) a control group that received no information about the drug, (2) a group that received information about only major side effects, (3) a group that received information about both major and minor side effects, and (4) a group that received information about only minor side effects.
They were then asked to make a serious of judgements about the drug, including risk, value, and effectiveness.
What they found:
When both major and minor side-effects are presented, consumers' judgments of the overall severity of side effects are diluted. Further, because of these diluted severity judgments, drug advertisements containing all side-effects are judged to be more attractive, less risky, and more effective.
If you hear a drug ad where the last symptom is something really minor, like itchy feet or sweaty palms, they want you to use that information to average the other things you remember with. The minor symptom inclusion waters down the whole thing.
Why this matters beyond drug ads:
These findings are generally applicable to all types of persuasive communication (my words, not theirs). Any situation where multiple attributes are presented, and some are more relevant or powerful than others - the dilution effect is in play.
The big take away:
The study included obviously irrelevant information - that had no direct bearing on the product's ability to deliver a specific benefit. The addition of this irrelevant information weakened consumers' beliefs in the product's ability to deliver the desired benefit.
How they looked at it:
A pretest was conducted to select the product information deemed to be either relevant or irrelevant. In each study, subjects were randomly assigned to one of two conditions: a supportive condition, in which they received only information that suggested the product would deliver the desired benefit, or a dilution condition, in which they received both supportive and obviously irrelevant information.
The researchers measured subjects' beliefs about the product's ability to deliver the desired benefit by asking them to rate their belief in the product's ability to deliver the desired benefit. The researchers then compared subjects' ratings of their beliefs in the product's ability to deliver the desired benefit between the supportive and dilution conditions.
What they found:
The results showed that adding irrelevant information weakened subjects' beliefs in the product's ability to deliver the desired benefit. This dilution effect was observed across 17 different products and services in 10 different studies.
Why this matters beyond product copy:
These findings apply generally to any form of marketing, and like the prior study, to most forms of persuasive communication. Adding more information at best muddies the water and confuses the audience, at worst makes the communication less persuasive.
Think about long FAQ sections, generated from the catalog of customer questions and support tickets. It seems like the helpful thing to do, list all the questions folks might have and give them clear answers. In reality, this is very likely reducing the appeal of whatever it is you want folks to do.
The big take away:
The study found that when consumers were overloaded with information, they spent more time making decisions, invested less attentional resources, and experienced more negative emotions, less decision satisfaction, and more buyer's remorse.
How they looked at it:
The researchers measured event-related potentials (ERPs) in their study by using electroencephalography (EEG) to record the electrical activity of the participants' brains while they were making buying decisions under different online information environments.
Alright, that sounds super interesting, but what the hell does it mean? In my words, the researchers scanned the brains of participants in two treatment groups:
High information (HAI) - 12 parcels of information
Low information (LAI) - 6 parcels of information
Then they compared the two conditions, quantitatively through the brain waves, and also through a brief survey (minor contribution from the survey).
What they found:
When consumers are overloaded with information, it leads to worse decision quality and experience. The study found that longer reaction times and more decision process regret are present when consumers are overloaded.
Why this matters beyond online shopping:
This is an old study from the early .com days. But it's not like the online CX has become cleaner since then - I'd argue the opposite has occurred. And therefore, I'd argue it's just as relevant today.
This is useful for both product designers and creators, as well as marketers and sales folks. Information overload should be a consideration when creating a customer interaction and something to always be on guard for.
I'll wrap this up with a few thoughts and the podcast I listened to that got me going on this. I think there's useful nuggets in what I wrote above, and certainly the rabbit hole goes way deeper (take a gander over here: https://www.connectedpapers.com). There is lots of research about the dilution effect in legal and policy domains. And now that you know about it, you'll see this everywhere as you go about your regular days.
Boiling all of this down to a simple heuristic:
Make things easy on your audience. Give them the most important information first and then let them guide into less important areas if they so choose.
And a simple framework:
For every new piece of information you want to add, ask: is this as strong/relevant/persuasive as the preceding information? If yes, maybe switch them. If no, leave it out.
Learn more about the effect in the real world: https://www.tutorai.me/modules/Real-world%20Examples%20of%20the%20Argument%20Dilution%20Effect
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