Friday, September 21, 2012

Beating a dead fish: more reasons to correct for multiple comparisons

Last night, the Ignobel prizes rewarded research using an fMRI on a dead salmon as an extreme case of a null effect.  fMRI machines identify over a hundred thousand of voxels (the tiny pieces they divide the brain into), and by chance some voxels show activity even where there isn't activity simply because of the sheer number of opportunities for a false positive: similar to how a broken clock is right twice a day, and if you looked at the clock 100,000 times, you would see several times when it said the correct time.  The researchers had a dead salmon complete a standard task that would be used on live human subjects and showed that --- without correcting for multiple comparisons --- the salmon appeared to be thinking.  With correction for multiple comparisons, the scientists saw no effects.  This research was published in the Journal of Serendipitous and Unexpected Results.

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