Cohen d for mixed effects model

0
votes

has anyone worked with the powerlmm package? I want to calculate statistical power for my model with the study_parameters command. It takes multiple values as input one of which is Cohen's d.

How do I figure out what is the Cohen d for my model? Also, for which effects exactly should I specify cohen d: for fixed, random or for the entire model?

p <- study_parameters(n1 = 6,
                      n2 = per_treatment(control=27, treatment=55),
                      sigma_subject_intercept = 4.56,
                      sigma_subject_slope = 0.22,
                      sigma_error = 5.39,
                      cor_subject = -0.19,
                      dropout = dropout_manual(0.0000000, 0.2666667, 0.3466667, 0.4666667, 0.47, 0.7333333),
                      effect_size = cohend(0.5), 
                                           standardizer = "posttest_SD"))
get_power(p)

Some details about the study:

  • 2 groups: Treatment and Control
  • 6 Timepoints
  • n(control)=27, n(treatment)=55

Thanks in advance for your answers.

1
rmixed-models

1 Answers

0
votes

  • You get Cohens d from the output of the function. I see you made a small error in your code. Delete the ")", after cohend(.05 and it works.

  • By definition, you are interested in the effect size of the fixed effect.

Hope it works out for you.