Why does a bipolar scale need indifference at zero for regression?
We have a bipolar scale that asks do you agree with A more or b more
It happened to be coded this way
(1) completely agree with A <--> (7) completely agree with B
So (4) is indifference
It should have been coded this way:
(-3) completely agree with A <--> (3) completely agree with B
So (0 is indifference)
In a regression our agreement scale is a control to see whether the difference between two conditions can be explained by agreement. E.g. person A seems to be liked significantly more, is this just because most people agree with person A more than person B. (Agree is the control and Like is DV).
If coded the first way there is a significant main effect of condition (p < .001) and the second way the main effect disappears (p = 0.546) (i.e. is explained by agreement)
I know the second way is correct but I didn't realise this would make a difference in regression. Can anyone explain why I need to make sure indifference is at 0 on bipolar scales? The only thing I can think of is that -3 and 3 have the same absolute value but 1 and 7 don't but I am not sure why absolute value needs to be calculated.