Birthdays, Letters and Biases

Reading Time: 4 minutes

Issue 13, Volume 112

By Alex Zheng 

Cover Image

Walking down the streets, your eyes wander from vehicle to vehicle, leading you to notice that on one of the license plates, the numbers match up with your own birthday. You think to yourself, “Wow that’s pretty cool!” or “Hey, it’s a sign! I’m important!” with a slight chuckle and a boosted sense of self-importance. You continue on your merry way, not thinking much more of the occurrence. However, it occurs again later, and you start pondering whether or not these are mere coincidences or warnings. Where are these numbers coming from? Why are they everywhere?

These were the questions Japanese psychologists Shinobu Kitayama and Mayumi Karasawa answered in their 1997 paper titled Implicit Self-Esteem in Japan: Name, Letters and Birthday Numbers. They determined that we have a special preference not only toward certain numbers but also letters. Their initial motive behind writing the paper was not actually to settle the question of the birthday-number effect, but to test another theory that questioned whether the Japanese population had a different sense and approach to self-esteem as compared to Americans or Europeans.

The two ran two studies that hid their assessment of the subjects’ self-esteem. In the first experiment, which involved letters, the scientists asked 219 undergraduate research students to rank a selection of 45 hiragana, the syllabic part of the Japanese writing system, based on how much they liked them. In the second experiment, the scientists asked 269 undergraduate students to rate the numbers zero to 49 based on attractiveness. Some numbers, like zero and 32 through 49, were actually cover-ups for the real range they wanted to investigate: one to 31, or the number of days in a month. In addition to these ratings, the scientists cleverly slipped in questions about the participants’ names and birthdays in addition to other pieces of demographic data.

The results were interesting, but not unexpected. The first experiment revealed the name-letter effect: the scientists consistently found that participants had a greater preference for letters that also appeared in their own names. This was attributed to a sense of identity and self-esteem tied to the name one is given at birth. Additionally, they also found that male respondents had a very strong preference for the first letters of their family name. This was likely a result of Japanese culture, where last names are inherited patrilineally from the father.

The second study revealed the birthday-number effect, in which the relative-liking score the scientists calculated was utilized to show that people disproportionately preferred the date of their own birth out of any number in the series. In addition, they found that this effect was stronger for numbers greater than 12. Scientists believe that this is because the likelihood of a two-digit number appearing in daily life is much less common than that of a one-digit number, so there is an especially strong reaction when they do appear. These larger numbers are also less likely to hold a “special meaning,” except when connected to one’s birthday. For instance, three is commonly called the “magic number,” but the number 22 does not really mean anything. Finally, a demographic study revealed that this effect was more pronounced in women than men, who showed a lower relative-liking score.

These results matched up with the researchers’ prior hypothesis that preference was based on some form of connection to oneself. These results also helped answer the researchers’ prior question about the self-esteem of the Japanese population: yes, Japanese people do feel self-esteem just like everyone else. However, they tend to hide away these feelings, which is likely the result of cultural upbringing. Overall, people tended to have positive feelings toward numbers or letters they associate with themselves, largely because most people like themselves.

In subsequent studies, scientists confirmed the same birthday-number effect on multiple occasions, including the 1997 study that asked US undergraduate students about their preference for certain numbers. This proved that cultural differences did not have an effect on the results of the experiments. Later studies also investigated the connection between the birthday-number effect and the letter-name effect as well as how automatic the preference process was.

The most interesting and applicable study on the topic was conducted by Coulter and Grewal, who investigated the effects of these preferences on consumerism. They demonstrated a positive relationship between the birthday-number and letter-name effect with a customer’s willingness to purchase a product. For instance, people preferred prices that began with the same letter as their name. Someone named Tom would prefer the price of twenty-two over other prices. In addition, people preferred price values that matched up with their birthdays. For instance, someone with a birthday of 9/16 would most strongly prefer an item with a price of $39.16 or $49.16. This might seem like an odd quirk of the effects at first, but large retail companies, especially online ones like Amazon can leverage these effects to increase a customer’s purchase intentions. This can easily be done using modern technology and information collected from the client. By tailoring the shopping experience using their demographic information, a company might be able to induce a customer to purchase more.

While more research is still needed regarding this retail strategy, and while scientists continue to discover more applications of this knowledge, the birthday-number and letter-name effect might simply remain an inconspicuous part of everyday life for everybody.