In a study with three treatments, A), A 2 , and A 3 , and a control group, C, dummy vectors were constructed as follows: subjects in Al were identified in D 1 , those in A 2 were identified in D 2 ,...

In a study with three treatments, A), A₂, and A₃, and a control group, C, dummy vectors were constructed as follows: subjects in Al were identified in D₁, those in A₂
were identified in D₂, and those in A₃
were identified in D₃. A multiple regression analysis was done in which the dependent variable was regressed on the three coded vectors. The following regression equation was obtained:

Y' = 8+6D1 + 5D2-2D3

(a) What are the means of the four groups on the dependent variable?

(b) What is the zero-order correlation between each pair of coded vectors, assuming equal n's in the groups?