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    Addendum: verbal and non-verbal intelligence changes in the teenage brain

    Ramsden, S. and Richardson, Fiona M. and Josse, G. and Thomas, Michael S.C. and Ellis, C. and Shakeshaft, C. and Seghier, M.L. and Price, C.J. (2012) Addendum: verbal and non-verbal intelligence changes in the teenage brain. Nature 485 , p. 666. ISSN 0028-0836.

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    We measured changes in intelligence quotient (IQ) between time and time in teenage subjects and searched their brains for regions where changes in IQ predicted changes in grey matter density (GMD). We found highly significant effects in two localized brain regions, after correcting for multiple comparisons across the whole brain. This provided an unbiased inference that longitudinal changes in IQ were meaningful rather than attributable to measurement error. In post hoc analyses, we quantified the (standardized) effect sizes2 by reporting that 20% of the variance in verbal IQ (VIQ) at time and 13% of the variance in performance IQ (PIQ) at time could be explained by changes in GMD at the most significant voxel in the regions identified by the whole brain analyses. These (in-sample) effect sizes pertain to the sample studied and should not be confused with out-of-sample predictions3: that is, IQ predictability given new or independent subjects. Out-of-sample predictions finesse the inherent sampling bias of (in-sample) effect sizes—known in neuroimaging as ‘the non-independence problem’.


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