[R-sig-ME] Predicting individual slopes from specific random intercepts

[Dominik Ćepulić]

Dear everybody!

I am writing with another question regarding lme4, this time regarding some
predicting possibilities.

Let´s say I predict variable Accuracy from Reaction time, random efffects
being subjects and tasks. The formula would be

glmer(Accuracy ~ RT + (1+RT | subj) + (1+RT | Task))

Random intercepts for subjects stand for their abilities, and random
intercepts for tasks for their difficulty.

I would like to be able to specify ability from a certain subject and the
difficulty of a task, and then predict the slope for this case in order to
plot the function.

Concretely, I would like to see how the function relating RT to Accuracy
looks like for people who are 1 sd above average in their abilities when
they solve tasks which are below average for their difficulty. The function
would then tell me how their probabilit of correct answer changes according
to the speed of answering.
For more clarity, you can also take a look at
*The Time on Task Effect in Reading and Problem Solving Is Moderated by
Task Difficulty and Skill: Insights from a Computer-Based Large-Scale
Assessment  *from Goldhammer et al.(2014). They did it in their last two
pictures I think.Thanks in advance,
Dominik

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