99 is much less than 100, even for large values of 99
Message #11 Posted by Frank Wales on 24 Mar 2003, 9:03 a.m.,
in response to message #10 by Frédéric
It's like psychological prices in shops. We are all enough intelligent not to be disturbed by these prices like $99,99 but the question is "why do sellers continue to mark such prices ???"
Because they work. People think 99 is noticeably cheaper than 100 because we are all endowed with a fuzzy sense of the relative sizes of numbers beyond about three, and so we give more weight to the most significant digits to help us get a sense of the quantities involved.
So, with 99 versus 100, '9' is clearly less than '10', and that kind of rough estimate is good enough for most things we have to do. The bigger the number gets, the harder we have to work to retain a sense of the true differences with any accuracy, and this makes it quite natural for us to think of 99 as significantly less than 100. It's not about intelligence, but about our apparent evolutionary heritage, since animals appear to have the same problems with precise counting beyond about three that we do.
(A good book on this topic is 'The Number Sense' by Stanislas Dehaene -- it's expensive, but worth the read.)
If you are genuinely unaffected by the difference between 99.99 and 100 in your buying behaviour, you are in a minority. Similarly, if your buying behaviour is unaffected by advertising, you are in a minority. Even though most people claim it doesn't affect them, it does anyway. (Try this thought experiment: you have to choose between two products, neither of which you've purchased before. Both appear to be of equal quality, and both are the same price. One is from a well-known company that advertises on TV; the other is from a company you've never heard of. Which one do you pick? Why?)
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