[R-sig-ME] whether the data can include participants compelete the questionnaire on only one accasion

[Ben Bolker]

    This is theoretically possible.
   For some degree of sparsity (i.e. a small enough fraction of 
participants with >1 observation) it will become computationally 
impractical/not worth the trouble.
    I would go ahead and try it out on your data.  Ideally you would try 
it out on some synthetic data, for example something like:

library(lme4)
set.seed(101)
subject <- rep(1:100, times = rep(1:2, each = 50))
x <- rnorm(length(subject))
dd <- data.frame(x, subject)
dd$y <- simulate(~ x + (1|subject),
                  newdata = dd,
                  newparams = list(beta = c(1,2), theta = 1, sigma = 1),
                  family = gaussian)[[1]]
lmer(y ~ x + (1|subject), family = gaussian, data = dd)


   (try something that matches your experimental/observational design 
reasonably well)

On 2022-06-06 2:56 a.m., Yanmin Wang wrote:
> it is known that linear mixed model is suitable for repeated measure. my longitudinal data is unbalanced, and many participants compelete the questionnaire on only one accasion. can i include these participants?
> any help is appeciated!
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-- 
Dr. Benjamin Bolker
Professor, Mathematics & Statistics and Biology, McMaster University
Director, School of Computational Science and Engineering
(Acting) Graduate chair, Mathematics & Statistics