The
Volcano Plot
tab, which is created when either of the inverse
variance
methods for combining
p-values
has been selected as the
Method to Use
and an
Effect ID Variable
has been specified, is shown below:
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When an inverse variance method has been used to combine
p
-values, a scatter plot shows the meta-analysis
p
-values and estimates of the overall effect. The
y
-axis
variable
of this scatter plot is the meta-analysis
p
-value, converted to the
-log
or
-log
10
scale if selected in the process
dialog
. The
x
-axis plots the estimate of the overall effect estimate for each effect, calculated by a weighted average of the individual study effects, where effect estimates can be
regression
coefficients or
log odds
ratios for example.
A horizontal reference line is drawn as a red, dashed line at the significance level that was specified. For
-log
or
-log
10
-converted
p
-values, effects above this line are significant; for
p
-values on the original scale, effects below the line are significant.