Multilevel mediation with missing data

[Adam Lekwa]

Greetings-

I am trying to fit a two level 2-2-1 mediation in which data are missing in the mediator and the outcome. For example:

m221 <- '
level:1
outcome ~ 1
level:2
outcome ~ b*mediator + c*treatment
mediator ~ a*treatment
indirect:= a*b
total:= indirect+c'

fit.m221 <- sem(m221, data = mydata, cluster = "ClassroomID", missing = "ml")

I'm receiving the following error, and am unsure if it is because of a problem in my dataset, or if I am hitting a bug:

"Error in utils::combn(ov.names, 2) : n < m"

Thanks in advance for any advice,

Adam

[Terrence Jorgensen]

I'm receiving the following error, and am unsure if it is because of a problem in my dataset, or if I am hitting a bug:

"Error in utils::combn(ov.names, 2) : n < m"

Many years ago, there was a bug preventing single-variable SEMs in lavaan; perhaps there is something similar going on here.  But perhaps the problem is that you are specifying an intercept at Level 1, which should be fixed to zero by definition.  Instead, try estimating outcome ~~ outcome.

Terrence D. Jorgensen

Assistant Professor, Methods and Statistics

Research Institute for Child Development and Education, the University of Amsterdam

http://www.uva.nl/profile/t.d.jorgensen

[Adam Lekwa]

Thanks, Terrence.

I'm getting the same error after making that change--it shows up with or without specifying outcome ~~ outcome at level 1. I should note that the error disappears and I can get this to run simply by changing "missing = 'ml' " over to "missing = 'listwise' ".

Thanks again,

Adam

[Yves Rosseel]

Hm. That sounds like a potential bug. Would you be able to send me a
minimal example (including a small dataset) to reproduce this error?

Please email it direclty to Yves dot Rosseel at UGent dot be

Yves.

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