Statistics – Category Size Bias

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Negotiators sometimes prey on the human tendency to believe outcomes are more likely to occur when part of a large category rather than part of a small category, regardless of the odds of the outcome. We tend to gravitate towards bigger number sets. When less may be more.


If lottery shoppers know that a corner store selected more lottery winners in the last 10 years than any other in the state, the corner store proudly advertises this fac and you may buy from that corner store, even though the odds are exactly the same. The higher frequency from that one store does not alter the odds of winning. They may have more winners because they sell more tickets than anyone else. A medium asks you to pick a letter they will not guess, they tell you there are 5 vowels and 21 consonants. You do not pick a vowel thinking they are less likely to guess that number. The odds are the same as selecting any single letter 1 out of 26. They primed your bias by mentioning an irrelevant statistic.


Do the math. The odds may be the same regardless of the outcome. There may be other factors operating. Use sound statistical sample size and then look at probability.

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