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Re: Telepathy/Parapsychology etc. and Meta-Analysis

 Stewart Robert Hinsley wrote:
 > In article <>
 >   "Damien Broderick" writes:
 > > Chris Lawson wrote:
 > >
 > > > Meta-analysis, IMHO, doesn't count. [...] This is a bit like
 > > > finding 3 inadequate samples of mince meat, and mixing all 3 in the mincer
 > > > again.
 > >
 > > Inadequate for what purposes?  You imply `tainted', but parapsychologists
 > > have tried (under the whip of their opponents, such as Hyman) to rid their
 > > data bases of contaminated data.  Are you really trying to tell us that
 > > adding 10 smallish samples together will not bring down the standard
 > > deviation, proportionately, to the point where an otherwise tenuous effect
 > > rises up over the noise level?  As you admit, pharmacologists use this
 > > procedure all the time.  It's not as compelling as levitating on to the White
 > > House lawn (and being shot out of the sky), but gimme a break here...
 > > Meta-analysis is acceptable in other fields.  Only an a priori conviction
 > > that psi is crap would make one *more* worried about its use in parapsych.
 > >
 > I'm fairly sure I've seen negative views of meta-analysis outside the
 > context of parapsychology. AFAIK, the problem is that meta-analysis can
 > introduce biases.
 > If one does enough experiments one will eventually get one with a result
 > a few standard deviations ought. Combining this with the rarity of the
 > publication of null results gives rise to a bias.
 > For example, consider a system in which there is no correlation between
 > a postulated cause and effect. Say 100 experiments are done, of which 80
 > give a null result, 10 give a borderline positive correlation, and 10
 > a borderline negative correlation. Say that of these 1/4 (20) of those
 > giving a null result, 1/2 (5) of those giving a negative correlation, and
 > all (1) of those giving a positive correlation, are published. In this
 > circumstance meta-analysis clearly gives rise to a misleading conclusion.
 > Another problem with meta-analysis is how to decide how to weigh the
 > various data sets. Giving them equal weightings is wrong. If the
 > experiments have no systematic errors then weighing them according the
 > sizes and standard deviations of the data sets is appropriate. (Someone
 > more statistically sophisticated then I am could provide you with the
 > equations.) It is not obvious to me that it is always possible to
 > produce objective weightings of the results of disparate parapsychological
 > experiments; but, if the meta-analyst unconsciously gives greater weight
 > to the positive results this skews the result of the meta-analysis.
 > --
 > Stewart Robert Hinsley             The adequate is the enemy of the good.
 Thank you, Stewart!
 You have put it succinctly. Damien Broderick said I "admit" that meta-analysis is used 
 in fields such as pharmacology. As I clearly pointed out in the original, I am 
 suspicious of meta-analysis in ANY field. Occasionally such studies are useful, but the 
 vast majority show a small effect with marginal statistical signifance, and therefore 
 tell us no more than that a PROPER study with a larger sample size is needed to assess 
 the hypothesis.
 I read a lot of medical data in my work, and the meta-analyses are weighted IMHO one