I have a question about interpretation for a bayesian model with a gamma distributed dependent variable.
I have a dataset containing 3 groups’ sentiment score data, from 0 to 4 (this is a continuous variable), and my goal is to determine if there is an effect by group.
After following many online tutorials, I settled on a gamma score (did LOO of different families) - model below:
This is what R returns for my BRM:
Family: gamma
Links: mu = inverse; shape = identity
Formula: sentiment ~ group + (1 | id)
Data: df (Number of observations: 1856)
Samples: 20 chains, each with iter = 2000; warmup = 1000; thin = 1;
total post-warmup samples = 20000
The output is as follows:
Group-Level Effects:
~id (Number of levels: 1856)
Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
sd(Intercept) 0.40 0.16 0.04 0.65 1.01 2289 2424
Population-Level Effects:
Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
Intercept 2.55 0.09 2.38 2.74 1.00 6787 13508
group 1.22 0.14 0.95 1.50 1.00 27476 15066
group . 1.29 0.15 1.00 1.58 1.00 24998 15147
Family Specific Parameters:
Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
shape 1.65 [![enter image description here][1]][1] 0.06 1.54 1.76 1.00 7659 11316
So group 2 and 3 are different in sentiment to group 1 (as 95%CI don’t cross 0) but how do I interpret the estimate? Do I need to log? Transform something? How would I make this into a sentence? I’m confused as when I plot the conditional effects, I don’t understand what is on the y axis? Attached is the plot.
Thank you for your patience in helping me to understand!