It says that a negative value is a compliment.
A positive value is a substitute.
However, if XED >1, then it is elastic. If XED <1 then it is inelastic.
Inelastic is therefore negative and elastic is positive.
I don't get the fact that if a compliment has a negative value, we can see that it can only be inelastic, but I feel like my reasoning is flawed. Please help?