I have the following regression, where I regress the consumption of gasoline on logarithmic variables.
Meaning of the variables is: pnc=price index for cars pg=price index for gasoline, puc=price index for old cars y=per capita disposable income, ppt=price index for public transportation pd=price index for consumer durables, d79=time dummy for the OPEC oil shock, 1 for the post-1979 period and 0 otherwise
I do not understand how to interpret d79lnpuc variable. Why after the 1979 crisis an increase in the price of old cars has a positive relation to the consumption of gasoline? I think that maybe people started to buy old cars, because of the increase in the price of gasoline. However, I do not see any connection with that and d79lnpuc having a positive coefficient.
I will be thankful for any suggestions and hints.