Comparing two groups with if statements

[Daniel Bakker]

Dear all,

For an assignment I am comparing means of willingness to pay (WTP) with willingness to pay repeat (WTP_R) under various conditions. I need to know if the mean of WTP_R is higher or lower for the following conditions:

willingness_to_Pay_Repeat - willingness_to_Pay if focus==0 & certainty==0
willingness_to_Pay_Repeat - willingness_to_Pay if focus==1 & certainty==0
willingness_to_Pay_Repeat - willingness_to_Pay if focus==2 & certainty==0
willingness_to_Pay_Repeat - willingness_to_Pay if focus==0 & certainty==1
willingness_to_Pay_Repeat - willingness_to_Pay if focus==1 & certainty==1
willingness_to_Pay_Repeat - willingness_to_Pay if focus==2 & certainty==1

It is a within-sample design since the subjects had first provided his WTP, and if he chose yes I want to repeat, he provided his WTP_R

Now I am not sure which test I can use for this, when trying a t-test, it gives me an error. ?

ttest willingness_to_Pay_Repeat if focus==0 & certainty==0, by(willingness_to_Pay)

--> more than 2 groups found, only 2 allowed

Can I just use normal regression analyses eg:

regress willingness_to_Pay_Repeat willingness_to_Pay if focus==0 & certainty==0

Or would you suggest something else? I looked up a Wilcoxon test but wasn't too sure.


Thanks,

Daniël