Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!caip!nike!ucbcad!ucbvax!decwrl!cooper@pbsvax.dec.com From: cooper@pbsvax.dec.com (Topher Cooper DTN-225-5819) Newsgroups: net.sci Subject: Re: Parapsychology: more on the decline effect. Message-ID: <4203@decwrl.DEC.COM> Date: Wed, 16-Jul-86 13:53:49 EDT Article-I.D.: decwrl.4203 Posted: Wed Jul 16 13:53:49 1986 Date-Received: Thu, 17-Jul-86 07:12:45 EDT Sender: daemon@decwrl.DEC.COM Organization: Digital Equipment Corporation Lines: 120 Bill Jefferys ({allegra,ihnp4}!{ut-sally,knew}!utastro!bill, bill@astro.UTEXAS.EDU) has proposed an explanation for the decline effect in parapsychology. Essentially he proposes that parapsychologists tend to "stick" with subjects who happen to score well initially (the reader is referred to <981@utastro.UUCP> for details). This would produce a decline effect by selection. He asks if this is "an unreasonable scenario." It is not unreasonable but it is irrelevant to what we have been discussing. There is not one "decline effect" but many. Among them is the run decline effect, the score-sheet decline effect, the run series decline effect, the experiment decline effect, and the subject decline effect. These differ in the unit over which the decline is measured. A run is a series of trials which are done essentially in "one go". Classically, a run corresponded to a single deck of 25 Zener cards. The run decline effect is the tendency for the average score for the first trials of an experiment to be higher than the second, which in turn is higher than the third etc. The score-sheet decline has to do with the old manual scoring sheets. It was found that there was a frequently a declining trend from the average of the first run on each sheet to the last run on each sheet. The run series decline is a tendency for scores to decline over runs in a run series. A run series a part of an experiment over which conditions for any given subject are held constant. The experiment decline is a tendency for the average score per run to decrease over the course of an experiment. The subject decline effect is the tendency for the performance of a subject used in a series of experiments to decline over time. It is frequently noted by researchers that good subjects seem to "burn out". These different decline effects can be put together into a single phenomena by assuming that there is a continuous decline for any given subject. Novel conditions seem to cause some recovery over the basic trend. This is, however, speculation -- the different decline effects may come from distinct causes. The best established of these effects are the run decline and the experiment decline. We have been very specifically speaking of the experiment decline. For example, in the article in which he makes this proposal Bill Jefferys quotes me as saying: >> . . . the decline effect >>in parapsychology (the tendency for the scoring rate to decrease over the >>course of an experiment) . . . Nowhere in this discussion has anyone disputed this definition. A properly designed experiment of the general form that a parapsychology experiment takes must include a clearly specified termination criteria. The termination criteria specifies when the experiment is to stop. The termination criteria must be shown to be independent of the hypothesis under study. Almost universally, the simple termination criteria of stopping when the/each subject has performed a specified number of trials is used. One therefore does *not* have some initially good subjects with many (declining) trials, and (many more) initially poor subjects with a few trials as required by Bill's hypothesis. In a given experiment one has one subject or several subjects with the same number of trials for each. The number of trials is determined before the experiment is conducted. The decline effect is then either demonstrated across all the subjects or for those subjects whose *total* score is the highest. Bill says that > This would happen even if the experimenter >tried to keep all subjects in to the bitter end of a prescribed number >of trials. but does not explain how -- presumably, by the experimenter failing. In such a case, the experimental protocol would have been violated. According to standard practice, either the experiment would have to be abandoned or the experimental report would have to mention this fact. Selection biases from weak subjects dropping out are well understood in parapsychology. Any analysis of such an experiment, for the decline effect or for any other purpose, would have to take this into account. The scenario you propose *might* explain the *subject* decline effect, but it requires that high psi scores be a result of chance. This is the one hypothesis which can be categorically rejected. The odds against the results of parapsychological experiments being due to chance rather than rather than one or more systematic biases (conventional or unconventional) are astronomical, to say the least. The odds against subject differences being by chance are only slightly smaller. A variant on this hypothesis might, however, reasonably explain the subject decline effect. If subjects' average score (as somehow magically measured independently of any experiment decline effect) tends to both increase and decrease over periods of years (e.g., oscillate) then subjects who are used repeatedly in experiments would tend to be selected when they are scoring high. Inevitably, they would show a decline over many experiments. As far as I know the subject decline effect has simply been an observation by experimenters. I know of no study which purports to demonstrate it as a consistent effect. It is therefore at best a very weakly demonstrated effect which is, nevertheless, plausible as an extrapolation of the experiment decline effect. This hypothesis, though interesting, does little to change this basic picture. >The effect could be compounded if there are biases (e.g., unconscious >cueing) which initially inflate scores, but which come under better >control as attention is focussed on a high-scoring subject. It would be except that care is, of course, taken to apply controls uniformly across subjects and across time. This is another form of the "incompetent experimenter" assumption. Topher Cooper USENET: ...{allegra,decvax,ihnp4,ucbvax}!decwrl!pbsvax.dec.com!cooper INTERNET: cooper%pbsvax.DEC@decwrl.dec.com Disclaimer: This contains my own opinions, and I am solely responsible for them.