Anthropic Bias

Anthropic Bias: Observation Selection Effects in Science and Philosophy (2002) is a book by philosopher Nick Bostrom. It investigates how to reason when one suspects that evidence is biased by "observation selection effects"—when the evidence has been pre-filtered by the condition that some observer was appropriately positioned to "receive" it. This conundrum is sometimes called the "anthropic principle", "self-locating belief", or "indexical information".

The book first discusses the fine-tuned universe hypothesis and its possible explanations, notably considering the possibility of a multiverse. Bostrom argues against the self-indication assumption (SIA), a term he uses to characterize some existing views, and introduces the self-sampling assumption (SSA). He later refines SSA into the strong self-sampling assumption (SSSA), which uses observer-moments instead of observers to address certain paradoxes in anthropic reasoning.