Statistical helper functions
There are many useful, but less-often called upon helpers in the umx library.
A great overview of these is sitting in the package help (
Have a read through. If there are any that are unclear, contact me, and I will add an explanation here.
As an example, we often want to residualise several variables prior to analysis. Sometimes even in wide data sets, but with the same residual formula for all copies of a variable in the wide dataset.
This can lead to complex, error-prone and lengthy code. For instance, in a recent paper, this is how I was residualizing some variables:
twinData$MPQAchievement_T1 <- residuals(lm(Achievement_T1 ~ Sex_T1 + Age_T1 + I(Age_T1^2), data = twinData, na.action = na.exclude)) twinData$MPQAchievement_T2 <- residuals(lm(Achievement_T2 ~ Sex_T2 + Age_T2 + I(Age_T2^2), data = twinData, na.action = na.exclude))
One complex line of code for each twin. And I repeated this for 10 more variables: 20 lines of complex code… Lot's of opportunity for a tupo ☺
You also have to remember to
umx_residualise this can be reduced in two ways. This one-line residualizes both twin’s data, and doesn’t require typing all the suffixes:
twinData = umx_residualise(Achievement ~ Sex + Age + I(Age^2), suffix = "_T", data = twinData)
umx_residualise can also residualise more than one dependent variable (though not with formulae yet). So this works:
twinData = umx_residualise(c("Achievement", "Motivation"), c("Sex", "Age"), suffix = "_T", data = twinData)
You could make it even briefer, but this is about where I am happy in terms of the brevity vs. explicit tradeoff.
On my TODO list are tutorial blogs about