I have a cortical composite ROI and I want to calculate an aproximate value of its thick average. This is my ROI:

"Executive" => ["caudalmiddlefrontal", "rostralmiddlefrontal", "superiorfrontal", "lateralorbitofrontal", "medialorbitofrontal", "parsopercularis", "parstriangularis", "parsorbitalis"]

I am going to calculate,

$$ T = \frac{\sum_{i}{T_i V_i}}{\sum_{i}{V_i}} $$

where $T$ is the whole thickness average and $T_i$ and $V_i$ are the thickness average and volume of the $i$th ROI respectively.

But remember you must correct it by ICV later

> a <- lm(x$Executive_ThickAvg~x$"EstimatedTotalIntraCranialVol_eTIV")
> b=a$coefficients[[2]]
> x$aExecutive_ThickAvg = x$Executive_ThickAvg -b*((x$EstimatedTotalIntraCranialVol_eTIV - mean(x$EstimatedTotalIntraCranialVol_eTIV, na.rm=TRUE)))

Also must do the same in Volume measurements

> a <- lm(x$Executive_Vol~x$"EstimatedTotalIntraCranialVol_eTIV")
> b=a$coefficients[[2]]
> x$aExecutive_Vol = x$Executive_Vol -b*((x$EstimatedTotalIntraCranialVol_eTIV - mean(x$EstimatedTotalIntraCranialVol_eTIV, na.rm=TRUE)))