I am rather new to STATA / statistics, so I wanted to see if I can get some help from the experts that browse talkstats.com.

As the subject line implies, I am trying to find the impact of marketing spend on sales. So the model I am looking at is sales as the dependent variable, and independent variables include a number of marketing channels (TV, print, direct mailing, etc.).

I don't think a simple multiple variable linear regression would be appropriate here, as the curve here should be a bit more interesting. I presume that there will be small gains to marketing spend in the beginning, and the impact to sales should increase once the spend goes above a certain threshold. Above a certain level of spend, I think the slope will decrease again when we reach diminishing returns.

Any idea how I might tackle this?

Thank you!