[R-sig-ME] mixed-effects model with partially nested fixed effects

[Yuqi Liu]

Hi R-experts,

  I am analyzing data from 3 experiments using linear mixed model. Each experiment had 2 fixed effects, movement type and motor effort. Movement type is shared by all experiments, motor effort varied but partially shared across experiments. The data looks like this:


  Subject              experiment        movement_type              motor_effort     DV

  1                           1                              synchronous                      normal
  2                           1                              asynchronous                    normal
   .
   .
   .

  101                       2                              synchronous                      normal
  102                       2                              asynchronous                    normal
  103                       2                              synchronous                      medium
  104                       2                              asynchronous                    medium
   .
   .
   .
  201                       3                              synchronous                      normal
  202                       3                              asynchronous                    normal
  203                       3                              synchronous                      hard
  204                       3                              asynchronous                    hard
   .
   .
   .
  I want to test if the effect of movement type differed across experiments and motor effort, but I am a little confused of how the model should be constructed in this case.

  My current model is :   model <- lmer(DV ~ movement_type * experiment/motor_effort + (1|subject), data). Is that correct in terms of my purpose?

  I am also wondering how to center independent variables in this case. For movement_type, I could code "synchronous" as "0.5" and "asynchronous" as "-0.5". For motor_effort, should I center them for each experiment separately, or across all experiment?

Thank you for your help!
Yuqi


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