``Mind over matter'' is a frequently used phrase, but is there any evidence suggesting that mind can exert some influence over the behaviour of physical, material systems? Two meta-analyses dealing with such effects will be reviewed, both of which suggest that mind can directly interact with matter. Both these databases involve participants attempting to make a random system behave in a non-random manner.
The first of these databases involves studies in which people
tried to influence the outcome of falling dice. This work was
initially suggested by claims of gamblers that they were able
to influence the outcome in dice throwing situations in gaming
casinos. Radin and Ferrari [25] conducted a meta-analysis of
148 dice studies conducted between 1935 and 1987. This database
also included 31 control studies in which no conscious influence
of outcome was attempted. The results showed a significant overall
effect for the experimental influence studies (
es = .012, Stouffer 
,
and chance results for the control studies
(Stouffer
z = 0.18). To obtain a homogeneous distribution of effect
sizes, 53 studies (35 per cent) of the database had to be deleted.
Of these deleted studies, 33 had positive and 19 had negative
effect sizes. Eleven study quality measures were considered.
While the relationship was not significant, the authors did find
that effect size decreased as study quality increased.
Another methodological problem affecting this database is that
the probability of obtaining a specific outcome is not necessarily
equally distributed across all the die faces (e.g., if using
pipped dice, the six typically has the least mass and is thus
most likely to come up). To examine the possible influence of
this ``non-random'' aspect of dice throwing, the results for
a subset of 69 studies, in which targets were balanced equally
across the six die faces, were examined. A significant overall
effect was still obtained (Stouffer
z = 7.617,
p 
). For these 69 studies, the effect size was
relatively constant across the different measures of study quality,
and a file drawer analysis revealed that a 20:1 ratio of unreported,
nonsignificant studies for each reported study would be required
to reduce the database to chance expectations.
The second ``mind over matter'' meta-analysis involves studies
in which a person attempts to influence a microelectronic random
number generator (RNG) to behave in a non-random manner. This
meta-analysis, conducted by Radin and Nelson [24], involves the
largest parapsychological database to date, with 832 series,
of which 597 were experimental series and 235 control series.
The general protocol of these studies involves having a RNG drive
a visual display, which an observer tries to influence, by means
of mental intention, in accordance with prespecified instructions.
The randomness of the RNG is usually provided by radioactive
decay, electronic noise or pseudorandom number sequence seeded
with true random sources; the RNG's are frequently monitored
to ensure true random output in these studies. The observer initiates
a ``trial'' by means of a button push, which starts the collection
of a fixed length sequence of data. For each data sequence, a
z score may then be computed. The mean effect size per
trial for the experimental series was very small, but very robust
(
es = .0003, combined
z = 15.58,
p = 
and significantly higher (
z = 4.1,
p = 0.00004) than the effect size for the control series
(
es = --.00004). Sixteen study quality measures were investigated;
effect size did not significantly co-vary with study quality.
The file drawer estimate for this data base is enormous, requiring
54,000 null, unreported studies to reduce the observed effect
to chance levels. Given these findings, Radin and Nelson concluded
that ``it is difficult to avoid the conclusion that under certain
circumstances, consciousness interacts with random physical systems''
(p. 1512, [24]).