Observation selection effect

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A selection effect exists when some property of a thing is correlated with its being sampled. The classic example is a phone poll sampling only those people who have phones.

An observation selection effect exists when some property of a thing is correlated with the observer existing in the first place. The study of such effects is sometimes called "anthropic reasoning" or "anthropics", after the anthropic principle.

Recent approaches to such effects have focused less on "anthropic principles" and more on possible assumptions such as:

  • The Self-Sampling Assumption, which performs a Bayesian update on the fact that you were randomly chosen out of the set of all observers.
  • The Self-Indication Assumption, which favors theories in proportion to the number of observers they predict, because with more observers, you're more likely to exist at all. (Sometimes, people take this to include the Self-Sampling Assumption, using "SIA" as shorthand for "SSA+SIA".)
  • Full Non-Indexical Conditioning, which performs a Bayesian update on the fact that there exists someone with your exact experiences.

One approach to anthropic reasoning that has sometimes been attempted is to derive principles from decision theory.

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