Towards a conceptual clarification and possible applications of Meehl’s crud factor: A preregistered systematic review

Paul E. Meehl’s crud factor posits that variables in the social and behavioural sciences are never entirely unrelated, encapsulated in the notion that “everything correlates with everything”. This preregistered systematic review examined how the crud factor and Lykken’s related concept of ambient noise have been defined, interpreted, and applied across research fields. We identified 424 works through database searches and citation tracking and analysed conceptual attributes and citation intentions. Among works allowing an inference about the relationship between the two concepts, the crud fact