The Mystery of the Decline Effect

Text and picture depicting propositions and scienticfi method

(c) 2009 Dave Gray (

There is a very, very strange phenomenon in scientific literature called the decline effect. For some inexplicable reason, many positive scientific effects seem to decline over time as more and more research into the effect is conducted. A theory that seems to be initially supported by overwhelmingly positive evidence can eventually wind up seeming significantly less supported; in some kind of weird way, it may seem like facts are becoming less factual over time.

For example, initial parapsychological research seemed to indicate evidence for psychic ability (ESP in particular), but this effect declined with subsequent studies. A subject of Joseph Banks Rhine who’d initially be able to guess cards vastly over chance in repeated tests gradually became worse at doing so. In fact, over the years this subject became able to guess cards barely above chance.

Jonathan Schooler, who posited the theory of verbal overshadowing, i.e. describing something impairs the ability to remember it more so than just observing something, noticed a similar decline in his results. Since the initial publication of verbal overshadowing theory in 1990, he’s found it increasingly harder to demonstrate positive results. He called it “cosmic habituation”, and joked that the cosmos was interfering in his studies.

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