Why am I asking you to do my dirty work? Here’s some data on the US new car market: cars sold and dealer advertising dollars. Why cars? I wanted an industry subject to cyclical downturns resulting from exogenous effects, like the current mortgage downturn. Also, I wanted an industry where I already had a whole bunch of data on my hard drive.
The correlation coefficient is -0.8. Although this data set is way too small to be very significant, it’s pretty darn suggestive. Data is all from the NADA.