estimate statement help

[ARC2]

Say a is 4 age groups and b is gender;

I want to compare age group 1 with age group 4 for the same gender. 

I think the estimate statements below will get me the means for two groups, but I have no idea how to write the statement that compares the two. Help would be appreciated.  Thank you. 

Proc glm or genmod or whateverl

class a b c;

model y= a b c;

run; 

estimate 'age group 1 female' int 1 a 1 0 0 0 b 0 1;

estimate 'age group 2 female' int 1 a 0 0 0 1 b 0 1;

[StatsMan · Accepted solution]

Since there is no interaction between age and gender, the difference between age groups will be the same for either gender.  Your ESTIMATE or CONTRAST would be

estimate 'age difference' age 1 0 0 -1;

You can get this by differencing the coefficients for the 2nd ESTIMATE statement from your first.  The coefficients on the intercept and on GENDER cancel out, leaving you with the coefficients above.