I have the following formula for a linear model:

z <- lm(y~x + factor(a) + factor(b), data=NT2010)

where a (groups) and b (Sub-groups) are categorical variables (factors), x
is a continuous covariate, and y the response variable.  Since b is nested
within a, the formula can also be written as: 

z <- lm(y~x + factor(a) + factor(a)/factor(b), data=NT2010)

and the same output is achieved when summary(z) is called.

How can I get the output to show all 3 groups that I have inputted?  There
are only group 2 and group 3 on the output, group 1 is missing.  Also there
is a subgroup (subgroup 1) of the total 9 subgroups missing.  I would like
to see the p-value of the missing group and missing sub-group even though
I'm sure they are not significantly different (>0.05).  How do I change the
original formula to get all groups and sub-groups outputted?

 

 


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