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

- Operating System: Windows 10
- brms Version: 2.8

I am a bit confused about the output, related to “family”, generated by the summary() function in brms.

For example, if I choose

family=Gamma(link=“log”)

in the summary() output I get:

Family Specific Parameters:

Estimate Est.Error l-95% CI u-95% CI Eff.Sample Rhat

shape 10.52 0.89 8.83 12.34 13619 1.00

Now, what is still confusing to me is why is it sufficient to only get an estimate for shape? What about the scale? Why is it not given explicitly?

In addition, if we consider

family=gaussian()

I understand it as a way to model the residuals, and that’s why when I get

output for family=gaussian():

Family Specific Parameters:

Estimate Est.Error l-95% CI u-95% CI Eff.Sample Rhat

sigma 28.56 1.33 26.09 31.31 112625 1.00

I understand it as saying that the residuals have a distribution N(0,sigma),

and, unsurprisingly, when I print the output of the predict()-function, I get estimates with

Est. Error approx equal to sigma.

But when it comes to interpreting the output of the family=Gamma(link=“log”)

I am not quite sure I know how to formulate it. What can we say about the Est. Error of the predictions, if we know that the shape of the response is shape=10.52?

I would really appreciate it if someone can give me some insight.