Academic journal article The Journal of Parapsychology

The Problem of Finding an Optimal Measure of Effect Size for Psi Experiments

Academic journal article The Journal of Parapsychology

The Problem of Finding an Optimal Measure of Effect Size for Psi Experiments

Article excerpt

ABSTRACT: The measurement of effect size (ES) has a long history in parapsychology, although the earlier attempts did not use this special statistical term. Already in 1935, R. H. Thouless presented an index of psi efficiency (later called ESP quotient) that measures the relative number of psi-effected (or "true") hits. He used a straightforward statistical derivation separating the hits into true hits and chance hits. Over the years, his index has been discussed and redefined by several authors, among them the present author, who termed it psi coefficient ([psi]) and derived an alternative index ([psi]') using an extended model in which the single trials are divided into several subtrials. Other parapsychologists used or discussed the ES measure z/[square root]n, which later became commonly used (e.g., Schmidt). At that time, however, most parapsychologists showed little interest in this topic.

No new developments arose until meta-analyses were introduced. Then the interest clearly increased, but it was directed to widely applicable ES measures, such as z/[square root]n. Thus it was overlooked that in ESP experiments a mixture of a perceptual and a guessing component is given, which outside parapsychology can be found only in a few multiple-choice designs. The necessary elimination of the guessing component can be obtained only by a special ES measure adjusted to this situation. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.