The frequency illusion is the experience of learning something new and then seemingly encountering it everywhere you look. You hear an unfamiliar word for the first time, and within days it appears in a podcast, a news article, and a conversation with a friend. You notice a particular car model, and suddenly the roads seem full of them. The phenomenon was formally named in 2005 by linguist Arnold Zwicky, who described it as the erroneous belief that a particular word or phrase occurs far more often than it actually does. But the illusion extends well beyond language, showing up in medicine, media consumption, law enforcement, and everyday decision-making in ways that can carry real consequences.
Where the Name Came From
Zwicky, a Stanford linguist, coined the term “frequency illusion” alongside a companion concept he called the “recency illusion,” which is the false belief that a word or usage is new when it has actually been around for a long time. Both terms emerged from his observations about how people talk about language. When someone notices a phrase they haven’t consciously registered before, two things tend to happen at once: they assume the phrase is new (recency illusion) and they assume it is suddenly being used far more than before (frequency illusion). In reality, the phrase was likely always there. Their attention simply hadn’t flagged it yet.1Languages. Are We Indeed So Illuded? Recency and Frequency Illusions in Dutch Prescriptivism
The popular name for this experience, the Baader-Meinhof phenomenon, predates Zwicky’s formal label and comes from a completely different corner of culture. The story goes that someone mentioned the Baader-Meinhof Group (a German militant organization from the 1970s) in a comment on a newspaper discussion board, and then started seeing references to the group everywhere. Other readers recognized the experience instantly. The name stuck because it was memorable and a little absurd, which is exactly why it spread online long before “frequency illusion” entered academic writing.
The Classic Everyday Examples
The easiest way to understand the frequency illusion is through the situations almost everyone has lived through at least once. You’re shopping for a particular car, say a silver Honda CR-V, and for the rest of the week every parking lot seems to be crawling with silver CR-Vs. They were always there. What changed is that your brain now has a reason to tag that car as relevant, so it gets promoted from background noise to conscious awareness.
The same thing happens with names. Expectant parents who settle on a name for their baby often start hearing it everywhere, sometimes to the point where they second-guess the choice, worried it’s become too popular. Usually it hasn’t. The name was in circulation all along, but it only started registering once it became personally meaningful. Pregnant people experience a version of this with pregnancy itself: once you’re expecting, it can feel like everyone around you is also expecting. The actual birth rate in your neighborhood didn’t spike. Your attentional filter just shifted.
Songs follow the same pattern. You hear a track at a friend’s house, and then it pops up in a store playlist, an Instagram reel, and a Spotify recommendation within 48 hours. Part of this can be algorithmic (Spotify genuinely is nudging you), but part is pure frequency illusion. The song was probably in those playlists before, and your ears simply passed over it.
How the Illusion Works in Your Brain
Two well-established cognitive tendencies work together to produce the frequency illusion. The first is selective attention. At any given moment, your brain is processing an enormous amount of sensory information. It cannot treat all of it as equally important, so it applies filters, prioritizing things that are new, emotionally charged, or recently relevant. When you learn a new word, decide on a car, or receive a medical diagnosis, your brain effectively turns up the volume on that specific signal. Instances that would have gone unnoticed yesterday now trigger a small flash of recognition.
The second ingredient is confirmation bias. Once you’ve noticed something twice, your brain starts building a narrative: “This thing is everywhere.” Each new sighting reinforces that story, while all the times you looked around and didn’t see the thing leave no impression at all. You remember the hits and forget the misses. Together, these two tendencies create a feedback loop. Selective attention delivers more sightings, and confirmation bias convinces you the sightings are meaningful rather than the product of a freshly tuned filter.
Language Prescriptivism and the Frequency Illusion
Zwicky coined the term because he kept seeing language commentators claim that some word or construction was used “constantly” or “everywhere” when corpus data showed it was actually quite rare. A Dutch study that tested this directly found the pattern was widespread in prescriptive writing about language. Commentators frequently used high-frequency terms like “often” or “constantly” when complaining about usages they disliked. When the researchers checked those claims against actual usage data, most of the prescriptive frequency statements turned out to be illusions. The commentators genuinely believed the usage was rampant, partly because noticing it once primed them to notice it again, and partly because prescriptive writing as a genre tends toward dramatic claims about linguistic decline.2Languages. Are We Indeed So Illuded? Recency and Frequency Illusions in Dutch Prescriptivism
This is one of the clearest documented cases of the frequency illusion operating at scale. A community of language experts, people who should be well-positioned to assess how common a usage is, systematically overestimated the frequency of the very things that annoyed them. The lesson generalizes beyond language: once something bothers you or interests you, your internal estimate of how often it occurs becomes unreliable.
Medical Student Syndrome
One of the most vivid real-world parallels to the frequency illusion plays out in medical schools. Medical student syndrome describes the well-known tendency for students studying diseases to start believing they have the symptoms of whatever illness they’re currently learning about. A student reading about multiple sclerosis notices a tingling in their arm that’s been there for months but never seemed worth thinking about. Another student studying cardiac arrhythmias becomes hyperaware of occasional skipped heartbeats that are completely normal.
The phenomenon has been documented for decades. Research at Menoufia University in Egypt confirmed that medical students score differently from non-medical students on nosophobia scales, showing heightened health anxiety that tracks with their disease-focused curriculum.3PubMed Central. “Medical student syndrome”: a real disease or just a myth?—a cross-sectional study at Menoufia University, Egypt A more recent analysis frames the syndrome not just as anxiety but as a reasoning error. Medical students learn extensively about serious diseases and their symptoms, which gives those symptoms high mental availability. When they then notice a symptom in their own body, they overestimate the probability that it signals something dangerous because the disease is mentally vivid and accessible, while the more relevant fact, that the base rate of that disease in their age group is extremely low, gets overlooked.4PubMed Central. Medical student syndrome: a bayesian reasoning failure
The frequency illusion operates here on two levels. First, the student’s new knowledge makes previously invisible bodily sensations suddenly salient, exactly the way a new word seems to pop up everywhere. Second, the student then overestimates how common or significant those sensations are, because their attention keeps landing on them and confirmation bias does the rest. The discomfort is real even though the underlying medical threat usually isn’t.
Media Coverage and Warped Risk Perception
Media exposure can act as an external engine for the frequency illusion on a societal scale. When news outlets disproportionately cover certain events, audiences don’t just overestimate how often those events happen. They sometimes change their behavior in ways that make things worse.
A study on cancer perception found that public estimates of how common different cancers are closely mirrored the distortions in news coverage rather than actual incidence data. Cancers that get heavy media attention, like blood cancers and brain cancers, were overestimated by the public, while cancers that are statistically common but receive less coverage, like bladder and thyroid cancers, were underestimated. Heavier news consumers were more prone to these distortions, suggesting the effect scales with exposure.5PubMed. Public estimates of cancer frequency: cancer incidence perceptions mirror distorted media depictions
This isn’t purely an academic curiosity. Research on transportation risk shows that when aviation accidents receive heavy media coverage, road traffic and fatal road accidents increase in the following months. The explanation is straightforward: people see plane crashes in the news repeatedly, overestimate the risk of flying, and choose to drive instead. But driving is statistically far more dangerous per mile traveled than flying. The media’s overrepresentation of rare but dramatic aviation disasters effectively pushes people toward the riskier option.6Social Forces. Do News Media Kill? How a Biased News Reality can Overshadow Real Societal Risks, The Case of Aviation and Road Traffic Accidents
In both cases, the mechanism echoes the personal frequency illusion but operates through the media environment rather than through individual learning. A plane crash dominates headlines, which makes aviation danger feel omnipresent. The many thousands of safe flights that happen every day leave no trace in memory. Selective attention and confirmation bias work the same way whether the triggering event is a word you just learned or a disaster you just saw on the news.
Criminal Profiling and the Illusion of Expertise
A less intuitive example of the frequency illusion at work involves criminal profiling in law enforcement. The public and many professionals believe that psychological profilers can meaningfully predict offender characteristics from crime scene evidence. Research into this belief has found it is sustained not by profiling’s track record but by the same cognitive patterns that drive the frequency illusion. People acquire information about profiling through anecdotes, repeated assertions that it works, and disproportionate emphasis on the cases where a profile happened to match the offender. The misses, and there are many, go unremembered.7SAGE Journals (Criminal Justice and Behavior). The Criminal Profiling Illusion
The researchers describe this as an “illusory belief” maintained by several factors: the creation of meaning from ambiguous information, the repetition of the message that profiling works, and the conferral of authority through the “expert profiler” label. Once someone believes profiling is effective, every case where a profiler’s prediction aligns even loosely with reality gets filed as evidence. Every case where it doesn’t fades into the background. This is the frequency illusion applied not to a word or a car but to an entire professional practice.
When the Illusion Turns Into a Decision
The practical danger of the frequency illusion is that it doesn’t feel like an illusion. When you notice something repeatedly, the experience of increased frequency is genuine, even if the actual frequency hasn’t changed. This makes it particularly hard to override, because you’re not reasoning from abstract statistics. You’re reasoning from lived experience, and your lived experience really does contain more sightings than before. The problem is that your lived experience is a biased sample.
This matters in contexts where overestimating frequency leads to action. A person who keeps noticing news about home burglaries in their city might invest in an expensive security system they don’t need because crime rates haven’t actually increased in their area. An investor who just learned about a particular market sector starts seeing “signs” that it’s about to take off, because every mention of that sector now registers as confirmation. A patient who Googles a symptom and reads about a rare disease will notice every subsequent twinge or ache that could plausibly fit, building a case for a diagnosis that a doctor would dismiss in minutes.
None of these people are being irrational in an obvious way. They’re responding to what their attention system is telling them. The frequency illusion is insidious precisely because the evidence it generates is experiential and personal, which makes it feel more trustworthy than dry statistics.
Can You Train Yourself Out of It
The honest answer is: probably not in any deep or lasting way. A systematic review of cognitive bias mitigation interventions found that the evidence for long-term effectiveness is thin. Out of 52 studies initially identified, only 12 adequately tested whether training effects persisted for at least two weeks, and just one examined whether the training transferred to different tasks or real-world contexts. The review concluded that there is currently insufficient evidence that bias mitigation interventions substantially help people make better decisions under real-life conditions.8PubMed Central. Retention and Transfer of Cognitive Bias Mitigation Interventions: A Systematic Literature Study
That doesn’t mean awareness is useless. Knowing the frequency illusion exists gives you a name for the experience, which can interrupt the automatic chain from “I keep seeing this” to “this must be happening more.” When you notice yourself thinking “wow, everyone is talking about X,” you can pause and ask whether everyone is actually talking about X or whether you just started paying attention to it. That pause won’t eliminate the illusion, but it can prevent you from making decisions based on a distorted sense of frequency.
Some practical habits can help. Checking actual data before acting on a “feeling” that something is increasing is the simplest one. If you think crime is spiking in your neighborhood, look at the police department’s published statistics before buying a security camera. If you think a particular baby name has become wildly popular, check the Social Security Administration’s name database. The illusion thrives in the gap between impression and data. Closing that gap, even partially, reduces its influence on the choices that matter.
The Frequency Illusion in Online Environments
Social media and algorithmic recommendation systems add a complication that Zwicky didn’t have to deal with in 2005. When you search for something online, click on a link, or linger on a post, algorithms take note and start serving you more of the same content. So when you notice a topic “everywhere” online, the frequency illusion and genuine algorithmic amplification can be happening simultaneously. You noticed the topic because your attention flagged it, and then the platform noticed you noticing and started feeding it back to you.
This makes it even harder to distinguish between “I’m seeing this more because I’m paying attention” and “I’m seeing this more because it’s genuinely trending.” In many cases, both are true at once, and untangling them is essentially impossible without stepping outside the algorithmic environment entirely. A useful mental shortcut: if you only notice the trend in your social media feeds and not in face-to-face conversations, there’s a good chance the algorithm is doing a lot of the heavy lifting.
The blending of genuine increased exposure and illusory increased frequency is one of the underappreciated features of living in an algorithmically curated information environment. It means the classic frequency illusion, where the external world stays the same and only your perception shifts, is increasingly rare in digital contexts. More often, your perception shifts and the world your screen shows you also shifts in response, creating a feedback loop that makes the illusion feel even more real than it would have in a pre-internet era.