Share on Facebook Share on Twitter Email
Answers.com

law of averages

 
Dictionary: law of averages

n.
The principle holding that probability will influence all occurrences in the long term.


Search unanswered questions...
Enter a question here...
Search: All sources Community Q&A Reference topics
Idioms: law of averages
Top

The idea that probability will influence all occurrences in the long term, that one will neither win nor lose all of the time. For example, If it rains every day this week, by the law of averages we're bound to get a sunny day soon. This colloquial term is a popular interpretation of a statistical principle, Bernoulli's theorem, formulated in the late 1600s.


WordNet: law of averages
Top
Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: a law affirming that in the long run probabilities will determine performance


Wikipedia: Law of averages
Top

The law of averages is a lay term used to express a belief that outcomes of a random event shall "even out" within a small sample.

As invoked in everyday life, the "law" usually reflects bad statistics or wishful thinking rather than any mathematical principle. While there is a real theorem that a random variable will reflect its underlying probability over a very large sample, the law of averages typically assumes that unnatural short-term "balance" must occur.

Examples

  • Belief that an event is "due" to happen: For example, "The roulette wheel has landed on red three consecutive times. The law of averages says it's due to land on black!" Of course, the wheel has no memory and its probabilities do not change according to past results. So even if the wheel has landed on red 10 consecutive times the probability that the next roll will be black is still 47.6% (it would be exactly 50% if there were no green zero). Similarly, there is no statistical basis for the belief that a losing sports team is due to win a game or that lottery numbers which haven't appeared recently are due to appear soon. This sort of belief is called the gambler's fallacy.
  • Belief that a sample's average must equal its expected value. For example, if one flips a fair coin 100 times, there is only an 8% chance that there will be exactly 50 heads.
  • Belief that a rare occurrence will happen given enough time: For example, "If I send my résumé to enough places, the law of averages says that someone will eventually hire me." This may actually be true assuming nonzero probabilities and that the number of tries is really large enough; the law of averages is then simply the Law of Large Numbers.
  • Belief that over time, statistics must accumulate to gradual even amount, regardless of the actual scenario. For example, the law of averages would expect that in a football league of ten teams, over a period of time each team would gradually balance out to have the same amount of wins and losses, regardless of how skilled or how unskilled any one team might be.

See also

References

  • Grinstead and Snell Introduction to Probability [1] is a Dartmouth College public-access text.

 
 

 

Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Idioms. The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Company. All rights reserved.  Read more
WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Law of averages" Read more