- Operating System: Windows 10 64-bit
- brms Version: 2.4.0

Is there a way in brms to specify a population-level effect for which some levels contain their own group-level effects? My dataset has the following unique factor combinations:

`Fluid Sample A A1 A A2 A A3 B B`

where Fluid A has samples from three subjects, A1-A3, but Fluid B has samples from only one subject. Fluids A and B can be thought of as test levels (e.g., drug vs no drug), so I want to treat Samples A1-A3 as group-level, but Fluid as population-level.

If both Fluid and Sample are treated as group-level effects, then I think the model would be

`y ~ (1|Fluid/Sample)`

but I’m not sure how to specify Fluid as a population-level in brms. Does `y ~ Fluid + (1|Fluid/Sample)`

make sense?

Thanks!