# Generalised Additive Mixed Model: Summary table differences between mgcv and brms

If you run an identical Generalised Additive Mixed Model with the `mgcv` vs. `brms` package in `R`, the summary tables for the factor smooth terms (e.g., `te(..., bs='fs', ...)` are different. For example, the generic model could be:

``````gam1 <-gam(DV ~
ExpTrialOrder +
FactorA +
s(CovariateM) +
s(ExpTrialOrder, Participant, bs='fs', m=1),
...)
``````
``````brms_gam1 <- brm(DV ~
ExpTrialOrder +
FactorA +
s(CovariateM) +
s(ExpTrialOrder, Participant, bs='fs', m=1),
...)
``````

For the traditional GAMM, the `s(ExpTrialOrder, Participant, bs='fs', m=1)` part of the table could look like this:

``````Approximate significance of smooth terms:
edf  Ref.df     F p-value
s(ExpTrialOrder,Participant) 134.282 368.000 59.88  <2e-16
``````

while the output from `brms` could look like this:

``````Smooth Terms:
Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
sds(sExpTrialOrderParticipant_1)     5.91      0.61     4.77     7.13 1.00     2333     4650
sds(sExpTrialOrderParticipant_2)   139.72     15.71   112.74   174.20 1.00      634     1720
``````

How should we read the summary table from `brms`? Are the two components (i.e., `_1` and `_2`) smooths for the two components of the `s()`; that is, Estimate == edf, for ExpTrialOrder and Participant, respectively?

• Operating System: macOS
• brms Version: 2.17.0

Thanks!

1 Like