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2012 ; 33
(1
): 1-13
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Minimizing within-experiment and within-group effects in Activation Likelihood
Estimation meta-analyses
#MMPMID21305667
Turkeltaub PE
; Eickhoff SB
; Laird AR
; Fox M
; Wiener M
; Fox P
Hum Brain Mapp
2012[Jan]; 33
(1
): 1-13
PMID21305667
show ga
Activation Likelihood Estimation (ALE) is an objective, quantitative technique
for coordinate-based meta-analysis (CBMA) of neuroimaging results that has been
validated for a variety of uses. Stepwise modifications have improved ALE's
theoretical and statistical rigor since its introduction. Here, we evaluate two
avenues to further optimize ALE. First, we demonstrate that the maximum
contribution of an experiment makes to an ALE map is related to the number of
foci it reports and their proximity. We present a modified ALE algorithm that
eliminates these within-experiment effects. However, we show that these effects
only account for 2-3% of cumulative ALE values, and removing them has little
impact on thresholded ALE maps. Next, we present an alternate organizational
approach to datasets that prevents subject groups with multiple experiments in a
dataset from influencing ALE values more than others. This modification decreases
cumulative ALE values by 7-9%, changes the relative magnitude of some clusters,
and reduces cluster extents. Overall, differences between results of the standard
approach and these new methods were small. This finding validates previous ALE
reports against concerns that they were driven by within-experiment or
within-group effects. We suggest that the modified ALE algorithm is theoretically
advantageous compared with the current algorithm, and that the alternate
organization of datasets is the most conservative approach for typical ALE
analyses and other CBMA methods. Combining the two modifications minimizes both
within-experiment and within-group effects, optimizing the degree to which ALE
values represent concordance of findings across independent reports.