Frequency illusion, also known as the Baader–Meinhof phenomenon or frequency bias, is a cognitive bias referring to the tendency to notice something more often after noticing it for the first time, leading to the belief that it has an increased frequency of occurrence.[1][2][3] The illusion is a result of increased awareness of a phrase, idea, or object – for example, hearing a song more often or seeing red cars everywhere.[4]

The name "Baader-Meinhof phenomenon" was coined in 1994 by Terry Mullen in a letter to the St. Paul Pioneer Press.[5] The letter describes how, after mentioning the name of the German terrorist group Baader-Meinhof once, he kept noticing it. This led to other readers sharing their own experiences of the phenomenon, leading it to gain recognition. It was not until 2005, when Stanford linguistics professor Arnold Zwicky wrote about this effect on his blog, that the name "frequency illusion" was coined.[2]


Several possible causes behind frequency illusion have been put forth. However, the consensus seems to be that the main processes behind this illusion are other cognitive biases and attention-related effects, that interact with frequency illusion.[1][2] Zwicky considered this illusion a result of two psychological processes, selective attention and confirmation bias.[3]

Selective attention

The main cause behind frequency illusion, and other related illusions and biases, seems to be selective attention. Selective attention refers to the process of selecting and focusing on relevant stimuli while ignoring distractions.[6][7] This means that people have the unconscious cognitive ability to filter for relevant information.

Seeing red cars all the time is a common real-life example of frequency illusion.

Selective attention is always at play whenever frequency illusion occurs.[2] Since selective attention focuses on information relevant to the individual, their experience of frequency illusion will also focus on the same stimuli. The process of frequency illusion is inseparable from selective attention, due to the cause-and-effect relationship between the two, so the "frequent" object, phrase, or idea has to be relevant or important to the individual.

Human cognition has two competing needs regarding attention – to solely focus on the task at hand but also to keep an eye out for dangerous stimuli.[8] This means that a particularly triggering or emotive stimulus could catch someone's attention, possibly more than a mundane task they are preoccupied with. Considering this, the assumption that more emotional or traumatic events are noticed more and better remembered, including in the case of frequency illusion, is likely.

Confirmation bias

Confirmation bias is a cognitive bias that always interacts with frequency illusion.[2] This bias refers to the tendency of seeking evidence that confirms one's beliefs or hypotheses, while sometimes overlooking evidence to the contrary.[8] Confirmation bias takes effect in the latter stages of selective attention, when the individual has already started noticing the specific stimuli. By focusing on this specific stimuli, the individual notices it more, therefore confirming their suspicions of it occurring more frequently, even though in reality the frequency has not changed. So, confirmation bias occurs when the individual affected by frequency illusion starts looking for reassurance of this increased frequency, believing their theories to be confirmed as they focus only on the supporting evidence.

Recency illusion

Recency illusion is another selective attention effect that tends to accompany frequency illusion. This illusion occurs when an individual notices something recently, leading them to be convinced that it originated recently as well.[3] This phenomenon amplifies frequency illusion since it leads the individual to become more aware of recent stimuli and increases the chances of them focusing on it in the near future.[9] Similar to frequency illusion, recency illusion is also a result of selective attention, and can be overcome by fact-checking.[2]

Split-category effect

Although more relevant to frequency estimations, though still a possible cause behind frequency illusion, split-category effect refers to the phenomenon when events are split into smaller subcategories, they can increase the predicted frequency of occurrence.[10] An example of this is asking an individual to predict the number of dogs in a country or asking them to estimate the number of Beagles, Labradors, Poodles, and French Bulldogs. Based on this effect, the sum of the latter would be larger than the former. Split-category effect could be causing frequency illusion in people – after subcategorizing an object, phrase, or idea, they might be likelier to notice these subcategories, leading them to believe the main category's frequency of occurrence has increased.[11]

Real-world examples


Frequency illusion is common in the linguistic field. Zwicky, who coined the term frequency illusion, is a linguist himself. He gave the example of how linguists "working on innovative uses of "all", especially the quotative use," believed their friends used the quotative "all" in conversation frequently. However, when the linguists actually transcribed these conversations, the number of times they used the quotative "all" was found to be significantly lower compared to their expectations.[2] This is most relevant when commentating on modern linguistic trends such as young people using specific phrases. When the phrases' actual frequency of use in the past is examined, however, it is revealed that they are much more frequent throughout history than initially predicted.[2]


In the field of medicine, frequency illusion could help doctors, radiologists, and medical professionals detect diseases. Rare diseases or conditions can often get overlooked by those in the medical field due to an unfamiliarity with the condition.[12] Medical researchers suggest that based on frequency illusion, medical professionals, especially those in training, could be primed to notice rarer patterns and lesions, which would lead them to detect rare diseases and conditions with higher accuracy.[13]


Frequency illusion is utilized by the marketing industry to make this cognitive bias work in their favour.[14] Generally, this is achieved by introducing a product through ads and familiarizing the consumers with it. As a result of frequency illusion, once the consumer notices the product, they start paying more attention to it. Frequently noticing this product on social media, in conversations, and in real life, leads them to believe that the product is more popular – or in frequent use – than it actually is.[4] Either due to a desire to conform or simply to own the product, the consumer eventually makes the purchase. This phenomenon is a marketing trick that increases the likelihood of the consumer buying the product.[14]

See also


  1. ^ a b van der Meulen, Marten (22 February 2022). "Are We Indeed So Illuded? Recency and Frequency Illusions in Dutch Prescriptivism". Languages. 7 (1): 42. doi:10.3390/languages7010042. hdl:2066/251971. ISSN 2226-471X.
  2. ^ a b c d e f g h Zwicky, Arnold (7 August 2005). "Language Log: Just between Dr. Language and I". Retrieved 2023-03-28.
  3. ^ a b c Zwicky, Arnold. (2006). Why Are We so Illuded? Stanford University.
  4. ^ a b "Frequency Illusion & Its Application in Modern Marketing – Galactik Views". 15 August 2021. Retrieved 2023-03-28.
  5. ^ "Sunday Bulletin Board: `I have dubbed it The Baader-Meinhof Phenomenon'". Twin Cities. 1994-10-16. Retrieved 2023-06-11.
  6. ^ Stevens, Courtney; Bavelier, Daphne (February 2021). "The role of selective attention on academic foundations: A cognitive neuroscience perspective". Developmental Cognitive Neuroscience. 2 (Suppl 1): S30–S48. doi:10.1016/j.dcn.2011.11.001. ISSN 1878-9293. PMC 3375497. PMID 22682909. S2CID 2637141.
  7. ^ Johnston, William A.; Dark, Veronica J. (January 1986). "Selective Attention". Annual Review of Psychology. 37 (1): 43–75. doi:10.1146/ ISSN 0066-4308.
  8. ^ a b Gray, Peter; Bjorklund, David F. (2018). Psychology (8th ed.). Macmillan Learning. ISBN 978-1-319-15051-8.
  9. ^ Bellows, Alan (March 2006). "The Baader-Meinhof Phenomenon". Damn Interesting. Retrieved 2023-03-28.
  10. ^ Fiedler, Klaus; Armbruster, Thomas (April 1994). "Two halfs may be more than one whole: Category-split effects on frequency illusions". Journal of Personality and Social Psychology. 66 (4): 633–645. doi:10.1037/0022-3514.66.4.633. ISSN 1939-1315.
  11. ^ Fiedler, K.; Unkelbach, C.; Freytag, P. (21 May 2009). "On splitting and merging categories: A regression account of subadditivity". Memory & Cognition. 37 (4): 383–393. doi:10.3758/mc.37.4.383. ISSN 0090-502X. PMID 19460947. S2CID 36501251.
  12. ^ Purohit, Kush (2019-06-01). "The Baader-Meinhof Phenomenon in Radiology". Academic Radiology. 26 (6): e127. doi:10.1016/j.acra.2019.01.025. ISSN 1076-6332. PMID 30738805. S2CID 73436033.
  13. ^ Kolli, Sindhura; Dang-Ho, Khoi Paul; Mori, Amit; Gurram, Krishna (3 May 2019). "The Baader-Meinhof Phenomenon of Dieulafoy's Lesion". Cureus. 11 (5): e4595. doi:10.7759/cureus.4595. PMC 6609307. PMID 31309020.
  14. ^ a b Kluchka, A. A. (25 October 2021) "Psychology in Marketing: The Baader-Meinhof Phenomenon". 12-14.