law of averages

law of averages

1. (statistics) The statistical tendency toward a fixed proportion in the results when an experiment is repeated a large number of times.

   Near-synonym: law of large numbers (not always differentiated)

   • 1919, William David Winter, Marine Insurance: Its Principles and Practice, McGraw-Hill, page 96:

     ... as they will not have sufficient distribution of risk to permit the law of averages to play its part and a severe total loss may ...

   • 1971, Russell Langley, Practical Statistics Simply Explained, Courier Dover Publications, →ISBN, page 22:

     Second Law - The Law of Averages. Whenever something (such as throwing a die) can have more than one result, if all the possible results have an equal chance ...

   • 1986, Geoffrey Grimmett, Dominic Welsh, Probability: An Introduction, OUP, →ISBN, page 124:

     It is upon the ideas of 'repeated experimentation' and the law of averages that many of our notions of chance are founded.

2. (informal) An imaginary or perceived "law" of probabilities which is wrongly used to predict results in the short-term.

   This coin has landed on heads ten times, so by the law of averages it must land on tails next time.

   • 1951, John Wyndham, The Day of the Triffids, Harmondsworth: Penguin Books, published 1954, page 7:

     In the nature of things a good many somebodies are always in hospital, and the law of averages had picked on me to be one of them a week or so before. It might just as easily have been the week before that - in which case I'd not be writing now: I'd not be here at all.

3. A real or purported law from centuries past regarding the distribution of recompense after a loss at sea due to an act of God, said by some (but not others) to explain why the word average evolved a sense having to do with means, medians, modes, etc.

• law of averages on Wikipedia.Wikipedia
• law of large numbers on Wikipedia.Wikipedia