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The birthday-number effect is the unconscious tendency of people to prefer the numbers in the date of their birthday over other numbers. First reported in 1997 by Japanese psychologists Shinobu Kitayama and Mayumi Karasawa, the birthday-number effect has been shown to hold across age and gender. The effect is most prominent for numbers over 12. Birth dates are unconsciously associated with the self, and most people like themselves; this has been offered as an explanation for the effect. Conversely, people who do not like themselves tend not to exhibit the effect. One lab study revealed an increase in favourable attitudes towards prices that were secretly manipulated to match the day of the month of the subjects’ birth, but a second study using birth year as price did not lead to the same result. People also have an unconscious preference for the letters in their name, and the two effects are significantly correlated. Another study found that participants with high self-esteem tended to prefer product names that included numbers from their birthday along with letters from their name. (Full article...)