What does this formula mean?
lmer(y ~ (1|g1/g2))
equivalently:
lmer(y ~ (1|g1) + (1|g1:g2)
According to the PDF that I found it in, linked here, it means:
"Intercept varying among g1 and g2 within g1"
I would love it if someone would elaborate on this, and would differentiate it from, say
lmer(y ~ (0 + g2|g1))
Thanks!