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Meta-anaiysTs cn Forced-Choicerrecognition Experiments
involving trial-by-trial feedback, 21 (43.8%) are significant at the 5% level.
None of the studies without subject feedback are significant
TABLE
8:
Feedback Received by Subjects
Feedback Level
N studies
Stoufferz
Mean ESeh
SDes %SIG.05
No Feedback
0.00
-0.002
0.027
0.0%
Delayed
2.27
0.009
0.035
23.8%
Run-score
4.80
0.024
0.047
333%
Trial-by-trial
7.59
0.048
0.094
433%
While trial-by-trial feedback is associated with the largest effect sizes and
significance levels, there is no evidence that subjects’ performance improved
over time.
Feedback level correlates positively though not significantly with
research quality (no3 = .134,p = .145). Inadequate randomization is the
most plausible source of potential artifacts in studies with trial-by-trial
feedback. We therefore performed a separate analysis on the 48 studies in
this group, blocking on the randomization and control quality measures.
Studies with optimal randomization do not differ significantly in either mean
significance level or mean effect size from those with suboptimal
randomization.
For significance
levels,
t
is 0.74 with 46 df (p = .465,
2-tailed). For ES,t
is 0.89 with 14 df(p = .525,2-tailed). Similarly, studies
reporting randomness control data do not
differ significantly in either
significance level or
effect
size from those not including randomness
controls. For significance levels, i is 0.25 with 46df(p = .803, 2-tailed). For
ES, t is 1.19 with 46 df(p = .241, 2-tailed).
Psychophysical Research Laboratories
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Meta-analysis of Forced-Choice Precognition Experiments
Time Interval
The interval between the subject’s response and target selection ranges
from less than one second to one year. Information about the time interval
is available for 145 studies. This information, however, is often imprecise.
Our analysis of the relationship between precognitive effect size and time
interval is therefore limited to seven broad interval categories: milliseconds,
seconds, minutes, hours, days, weeks, and months.
Although it is confounded with the feedback variable, there is a significant
decline in precognition significance levels and effect size over increasing
temporal distance. Using significance levels, r is -.270 with 143 df (p - .001,
2-tailed). Using effect sizer is -.206 (p = .013,2-tailed). The largest effects
occur over the millisecond interval (N = 31 studies, Stoufferz = 6.12, mean
ES = 0.046, sd =
.072). The smallest
effects occur over periods ranging
from a week to a month (N =
17, Stoufferz = -.36, mean ES = -0.004, sd
= .032).
Significance levels and effect sizes by precognitive interval are displayed
in Figures 7 and
8.
(The intervals are labelled numerically:
1 = msec.,
2 = sec., 3 = min., 4 =
hr., 5 = days, 6 = weeks, and 7 = months).
Curiously,
this finding results entirely from studies using unselected
subjects (ri23 = -.238, p =
.008, 2-tailed).
Studies with selected subjects
show a nonsignificant positive relationship betweem ES amd time interval
(ri8 =
.081, p =
.734,
2-tailed) and the difference between these two
correlations is itself significant (z = 2.58,/? = .01,2-tailed). This suggests
that the origin of the decline over time may be motivational rather than the
result of some
intrinsic physical boundary condition.
The relationship
between precognitive effect size and feedback also supports this conjecture.
Nevertheless, any finding suggesting potential boundary conditions on the
phenomenon should be vigorously pursued.
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^
Meta-analysis of Forced-Choice Precognition Experiments
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i
FIGURE 7: Significance Level by Precognitive Interval
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