I am using the
lmer function in R to examine the effect of skill (continuous) and context on eye movement data. I am new to
lmer and not by nature statistically inclined. It is my understanding that it is best to include random intercepts and random slopes for subject and item like below.
However, I am particularly interested in the effect of skill on the eye movement record. It seems to me that the subject random effect may be diminishing the ability of the model to find significant skill interactions with context (condition). Am I correct in thinking the subject random effect is parceling out the variability for my skill measure?
Also, I am really only interested in those who scored either high or low on the skill measure. The dataset I am using contains those in the middle where there is a lot of variability. Would it be appropriate to remove these subjects from analysis?
Finally, I am unsure whether or not subject should be nested within skill as each subject was given only one value for skill.
Any guidance would be greatly appreciated.