maxsum vs. maxsumt

Eric Maris maris at NICI.RU.NL
Mon Dec 5 22:05:00 CET 2005

Hi Michael,

> I just noticed that my version of clusterrandanalysis (20051127) doesn't
> list the teststatistic 'maxsumt' in its header or in the actual code as it
> is used in the tutorial (toolkit 2005). Instead there's an option (the
> default) 'maxsum'. Are these two the same - or is maxsum just the summed
> raw effect within a cluster ( and thus maybe pretty sensitive to extreme
> outliers), whereas maxsumt refers to summed t-scores from the initial
> tests performed for cluster finding?

The change from 'maxsumt' to 'maxsum' occured when clusterrandanalysis also
supported F-statistics at the level of (sensor,frequency,time)-triplets.
Using 'cfg.clusterteststat=maxsum' in combination with
'cfg.statistic=indepsamplesT' gives the same results as the 'maxsumt'-option
of the older version of clusterrandanalysis.

> I also notice that maxsum 'always' yields more significants clusters than
> orderedsums, is there an explanation for this behaviour (I thought it
> might rather be the other way round...)?

I am not surprised. The behavior of 'cfg.clusterteststat=orderedsums'
depends on the value assigned to 'cfg.smallestcluster'. If you give
'cfg.smallestcluster' a small value, this will reduce the sensitivity for
larger clusters (larger than this small value). The option
'cfg.clusterteststat=orderedsums' will result in more significant clusters
than obtained with 'cfg.clusterteststat=maxsum' if the data contain one big
cluster and a number of much smaller (but systematic) clusters. These
smaller clusters may become significant with
'cfg.clusterteststat=orderedsums' if their size is larger than
'cfg.smallestcluster'. The value of 'cfg.smallestcluster' should be
determined independently of the data. I guess there is no need to explain
why this so.


Eric Maris

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