[R-sig-ME] A conceptual question regarding fixed effects

Simon Harmel @|m@h@rme| @end|ng |rom gm@||@com
Thu Aug 12 23:52:27 CEST 2021

Dear Colleagues,

Can we say in mixed-effects models, a fixed-effect coef. is some kind of
(weighted) average of its individual regression counterparts fit to each
level of a grouping variable and that is why fixed-effect coefs in
mixed-effects models can prevent things like a Simpson's Paradox case (
https://stats.stackexchange.com/a/478580/140365) from happening?

If yes, then, would this also mean that if we fit models with the exact
same fixed-effects specification but differing random-effect
specifications, then the fixed coefs can be expected to be different in
value but also meaning (i.e., what kind of [weighted] average they

For example, would the meaning of a fixed-effect coef. for variable X
change if it has a corresponding random-effect in the model vs. when it
doesn't, or if we allow X to vary across levels of 1 grouping variable (X |
ID1) vs. those of 2 nested grouping variables (X | ID1/ID2)?

Many thanks for helping me understand this better,

	[[alternative HTML version deleted]]

More information about the R-sig-mixed-models mailing list