Assume regression y=f(x). Now you say y increases as x decreases?
Sorry what I meant was in a time series context.
Say you have this regression:
where y_t is a positive trending time series variable and x_t is a negative trending time series data, in general would it be a good idea to add a time trend variable if the dependent variable is upwards trending and the independent variable is downwards trending? Ie, use the regression: