Calculating group differences

Hi everyone,

I am trying to compute the overall posterior differences between groups (A - B = 0) from a brmsfit object using the hypothesis function but I am unsure I am performing it correctly with the interaction term so I would love a bit of advice.

The structure of my model is as follows:
prop_mod=brm(prop_links~0+PolOrder*clim+(1|Reference/Network), family=Beta(link = "logit"), inits=0, prior=propprior, data=g.sub,cores=4)

Prop_links= proportion of network links
PolOrder = Pollinator insect order (6 groups: Bee, Coleoptera, Diptera, Hymenoptera, Lepidoptera and Syrphidae)
clim = Climate zone (5 groups: A, B, C, D, E)

As such, I am interested in differences between PolOrder group within each clim.

With considering climate A (the reference level of clim) I have performed the following when considering bees (the reference level of PolOrder) with Syrphidae:
hypothesis(prop_mod,alpha=0.05, c("PolOrderBee - PolOrderSyrphidae = 0")

And within a different climate I have done as follows, adding in the interaction:
hypothesis(prop_mod,alpha=0.05, c("(PolOrderBee + climB) - (PolOrderSyrphidae + climB + PolOrderSyrphidae:climB) = 0"

These appear to give me sensible results but id love some clarification as similar posts I have read aren’t exactly like my case.

Also, am I missing something in the hypothesis output or is it possible to get a numeric value how far the expected value under the hypothesis lies outside the 95%-CI as well the *

Thanks in advance,

Please also provide the following information in addition to your question:

  • Operating System: MacOS High Sierra
  • brms Version: 2.5.0