Timeline for Should a nested random effect be included if it has only one level for ONLY ONE fixed effect level?
Current License: CC BY-SA 4.0
9 events
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| Apr 18, 2020 at 23:53 | vote | accept | amateur3057 | ||
| Apr 18, 2020 at 23:53 | vote | accept | amateur3057 | ||
| Apr 18, 2020 at 23:53 | |||||
| Apr 18, 2020 at 23:46 | comment | added | Noah | You would have to create dummy variables for all but the reference level of the factor and then enter those as 19 separate variables. In PROC MIXED you can use the RANDOM statement to choose which variables get random effects. | |
| Apr 18, 2020 at 23:33 | comment | added | amateur3057 | I've never heard of specifying which levels of a factor should have random slopes, either in R or SAS. How would I go about doing that? | |
| Apr 18, 2020 at 23:21 | comment | added | Noah | With multiple groups with only one level, you still need the reference group to be one of those with one only level, but the others that only have one only level can be entered as normal, just with no random slopes on them. You get to choose where you put the random slopes so you can omit the groups that shouldn't have it. | |
| Apr 18, 2020 at 23:19 | comment | added | Noah | I think you have to allow the 1-level group to be the reference category because that would be the only way to prevent it from having a random component by omitting a random slope. If the reference group has nesting, then you have to allow a random intercept, which forces all group means to vary. You should just fit your model and perform any comparisons you want using planned contrasts afterward. | |
| Apr 18, 2020 at 23:13 | comment | added | amateur3057 |
Also, is there a more general strategy than setting the troublesome group level as the reference, since these experiments are performed regularly and it could easily be the case that there are multiple troublesome group levels (i.e. which only have a single corresponding nested level)?
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| Apr 18, 2020 at 23:09 | comment | added | amateur3057 |
If the experimental design suggests a different level of group as the reference, is there another strategy? This is the case in my scenario, where it was a planned experiment and it wouldn't make sense to report the results with reference to a non-control level.
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| Apr 18, 2020 at 22:50 | history | answered | Noah | CC BY-SA 4.0 |