Does Advertising Actually Work?

 Freakonomics, 441. Does Advertising Actually Work? (Part 2: Digital)   (Part 1: TV)

行銷的關鍵是要確定因果和相關，例如某大零售商一年只有在三個重要節日做廣告，銷售量的增加是因為季節效應、還是廣告？在這個有趣的節目裡面，和 eBay 合作的經濟學家，做了一個 A/B 測試實驗，說明其搜尋引擎關鍵字廣告效果有限。當時的 eBay 總經理因此決定縮減一億美元的線上廣告預算。

T. Blake, C. Nosko, and S. Tadelis, Consumer heterogeneity and paid search effectiveness: A large‐scale field experiment, Econometrica, 83 (1), pp. 155-174, 2015.

Our experiments show that the effectiveness of SEM is small for a well-known company like eBay and that the channel has been ineffective on average....

We then use our experimental methods that control for endogeneity to find a ROI of -63%, with a 95% confidence interval of [-124%; -3%], rejecting the hypothesis that the channel yields positive returns at all.