Section 12. 4 Figure 12.8 about statistical_rethinking_with_brms_ggplot2_and_the_tidyverse_2_ed HOT 3 CLOSED

Hey @icrichmond, I can see your point. I actually think the plot in McElreath’s text (p. 396) is misleading and probably based on a typo in his code. The lowest educational category is Elem. Since this would be treated as the reference category for the simplex, it would be assigned delta[0]. Further, within the context of the simplex, delta[0] is not a parameter, but is fixed to zero. You can get a sense of this on page 394 in the text. If you were to base the results on McElreath’s rethinking and base-R code, I think he’d need to change his R code block on page 395 to read:

delta_labels <- c("Elem","MidSch","SHS","HSG","SCol","Bach","Mast","Grad") 
pairs( m12.6 , pars="delta" , labels=delta_labels[-1])

from statistical_rethinking_with_brms_ggplot2_and_the_tidyverse_2_ed.

Ahhhh okay, I see what you mean and you're absolutely right - on p. 392 of the text he even says

"The first level (Elementary School) will be absorbed into the intercept. Then the first increment comes from moving Elementary School to Middle School"

I was misinterpreting because of the previous section, where on p. 383 he mentions:

"Since the largest response value always has a cumulative probability of 1, we effectively do not need a parameter for it"

Thanks so much for your response and apologies for the unnecessary issue!

from statistical_rethinking_with_brms_ggplot2_and_the_tidyverse_2_ed.

Yep, the whole thing is very tricky. Thanks for reporting your concerns and for the kind words, above.

from statistical_rethinking_with_brms_ggplot2_and_the_tidyverse_2_ed.